5.  Batch Processing 

5.1   Introduction
Batch processing is accomplished by invoking sequentially and with appropriate input files the GAMIT modules that perform the required computations.  The command or "batch" files to invoke the modules are created, for each standard type of analysis, by program FIXDRV.  The batch run set up by FIXDRV would typically go through some or all of following steps:

	If not done done in preprocessing (see Chapter 4.10)
	•	generation of an orbital ephemeris with partials
	If good a priori coordinates are not available (see Chapter 4.2)
	•	generation of residuals to the a priori  model and partial derivatives of the 		residuals with respect to the parameters
	•	automatic edit of residuals
	•	"quick" solution to flatten the residuals and/or to improve the a priori orbital 		parameters and/or station coordinates
	•	regeneration of the orbit using the improved orbital parameters
	Always
	•	generation of residuals and partials 
	•	automatic edit of  residuals
	•	"final" solution
	•	automatic scan of postfit residuals to detect cycle slips

For most data sets the processing will proceed through these steps without manual intervention.  You can then visually inspect the solution and editing summaries to determine if further processing is necessary.  If so, you may repeat the solution by executing just the final steps in the batch file or, less often, by rerunning FIXDRV to set up a different sequence as described below.  

If you have prepared the data in a "day" directory as described in Chapter 4, then you should have available as files or links all of the tables necessary to run FIXDRV and to execute the GAMIT batch run:  station and scenario tables (station.info and session.info), ephemerides (G- and T-files),  raw observations (X-file), satellite and station clock values (J- and K-files), a priori station coordinates (L-file), lunar and solar ephemerides (luntab. and soltab.), and tables for earth rotation values (nutabl., ut1., and pole.), TAI-UTC (leap.sec), geodetic datums (gdetic.dat), antenna phase-center offsets or models (antmod.dat), receiver and antenna names (rcvant.dat), and satellite yaw parameters table (svnav.dat).  Three additional files are needed:  the list of X-files to be processed (D-file), and control tables for the analyses (sestbl. and sittbl.)  These can be easily created from templates (from gamit/example), as described below.  If you have used MAKEXP for data preparation, you will have already a D-file. 

5.2  Running FIXDRV

FIXDRV has three primary inputs:  1) a D-file containing the names of the satellite ephemeris (T-), clock (I- and J-), and observation (X- or C-) files to be used;  2) a session control table (sestbl.) containing analysis commands; and 3) a site control table (sittbl.) specifying a priori constraints for coordinates and station-specific models.

An example of a D-file (named dvent7.278)  is given below, with comments added at the right:
1	number of solutions
2	number of sessions
lvent7.278	L-file for all sessions
tvent7.278	T-file for all sessions
ivent7.278	I-file for all sessions            (end of global files)
jvent7.278	J-file for session 1
3	number of stations (x-files) in session 1
xcato7.278	
xsafe7.278	
xlove7.278	
jvent7.279	J-file for session 2
2	number of stations (x-files) in session 2
xcato7.279
xsafe7.279

The integer on the first line gives the number of independent solutions to be performed; if greater than one, it indicates that you have concatenated essentially independent runs for serial processing. The integer on the second line indicates the number of sessions in this solution; in the example the data from two sessions (days) are to be used simultaneously to estimate the station coordinates and orbital parameters.  With widespread use of GLOBK, GAMIT runs involving more than one session or solution are rare, so in most cases the first two lines of the D-file will each contain "1" and the last four lines shown above will be omitted.  Lines 3–6 contain the name of the coordinate (L-) file to be read, the ephemeris (T-) file to be read or created, and the name of the I-file to be read or created.  The I-file is now optional and can be left blank or set to 'NONE' if you don't have K-files readily available from which to calculate clock rates.  In this case, you must specify 'Use I-file = N' in the sestbl. (see below). The use of an I-file is recommended because modeling of the dominant drift in the receiver clock minimizes the danger of numerical problems in SOLVE due to large jumps across gaps of several hours.  For each session there is the name of the satellite clock (J-) file to be used, an integer giving the number of stations, and the names of all of the X-or C-files for that session.  The names of other files to be read or created are assigned by FIXDRV: the G-filename from the T-file name; the K- and P-file names from the X- (or C-) file name; and the H-, M-, O-, Q-, and V-file names from the D-file name.

A session control table (sestbl.) with only the required and commonly used entries is shown below.  (See Table 5.1 for a complete list of entries.)

 Session Table                        
---------------

Processing Agency = MIT

Station Number = *
Satellite Number =  *

Station Constraint = Y      ; Y/N  
Satellite Constraint = Y    ; Y/N  (next two lines free-format but 'all' must be present)
    all     a     e    i      n     w    M    rad1  rad2  rad3  rad4 . . . rad9
          0.01  0.01  0.01  0.01  0.01  0.01   5     5.    1.    1. . . . . 1.

Type of Analysis = 0-ITER       ; PREFIT / QUICK / 0-ITER/1-ITER/2-ITER  
Choice of Observable = LC_HELP  ; L1_SINGLE/L1&L2/L1_ONLY/L2_ONLY/LC_ONLY/
                                ; L1,L2_INDEPEND./LC_HELP
Choice of Experiment = RELAX.   ; BASELINE/RELAX.
Data Status = RAW               ; RAW/CLN 

Initial ARC = No               ; Default YES with RELAX, NO with Baseline. 

Inertial Frame = J2000          ; B1950/J2000; default J2000

AUTCLN Command File = autcln.cmd ; Default none (use default options in AUTCLN)

Zenith Delay Estimation = Yes   ; Yes/No
Number Zen = 4                  ; number of zenith-delay parameters
Atmospheric Gradient = Yes .....; Yes/No  (default no)
Elevation Cutoff = 15.          ; Applied in SOLVE, overrides MODEL and AUTCLN values 

Antenna Model = ELEV            ; NONE/ELEV/AZEL  default = NONE

Estimate EOP             ; Binary coded: 1 wob  2 ut1  4 wob rate  8 UT1 rate; default 15 
Wobble Constraint        ; [pole] [pole rate]  default = 3. 0.3  (arcsec) (arcsec/day)
UT1 Constraint           ; [UT1] [UT1 rate]    default = 0.00002 0.02 (sec)  (sec/day)

Ionospheric Constraints =  0.0 mm + 8.00 ppm ;  default = 1 ppm
Ambiguity resolution WL         ; default = 0.15 0.15 1000. 10. 500.
Ambiguity resolution NL         ; default = 0.15 0.15 1000. 10. 500.

Each command is recognized by the keywords at the beginning of the line.  They must begin in column one and be spelled out completely and correctly but are not case sensitive.  The keyword answer must begin exactly one space after the equal sign.  The order of the commands in the files is not important except for the satellite constraints, which must followd the Satellite Constraint keyword.    After the semi-colon on each line is a summary of keywords for all the options available.  These are simply comments in the session table.

In the example shown, the first input is a 3-letter code for the analysis group.  This is required in order to force identification of a solution on the h-file.  The next two entries, giving the number of stations and satellites (the * means to use all stations or satellites). are required but currently serve no useful function since the exclusion of stations and satellites must be accomplished by editing the SOLVE batch file.  (We hope to reinstate this feature in FIXDRV and the sestbl. in the future.) 

Next, the user specifies whether a priori  constraints are to be used for stations and satellites.  The station constraints are applied globally (not session by session); the actual constraints are set in the site control (sittbl.) file.  For satellite constraints, if All is found in the header line, as shown in the example, only one entry is required, with values applied to all satellites.  If you need to specify different constaints for different satellites, there must be entries for all satellites in the scenario, in the following format:

Satellite Constraint = Y         ; Y/N                    
    ch#     a     e    i      n     w    M    rad1  rad2  rad3  rad4. . . rad9
   NO.1 = 0.01  0.01  0.01  0.01  0.01  0.01   5     5.    1.    1. . . . . 1.
   NO.2 = 0.01  0.01  0.01  0.01  0.01  0.01   5.    5.    1.    1. . . . . 1.
....
   NO.30= 0.01  0.01  0.01  0.01  0.01  0.01   5.    5.    1.    1. . . . . 1.

In both examples, there should be entries for 9 non-gravitational force ("radiation-pressure") parameters (only 5 are shown because of the limited page width).  The constraints are given in parts per million (ppm) for the initial conditions and percent for the non-gravitational force parameters (in contrast to GLOBK which expects m and m/s for initial conditions and a fraction of unity for the non-gravitational force parameters).  The values shown (0.01 ppm or 20 cm for initial conditions, 5% for the direct radiation-presssure and y-bias coefficients, and 1% for the third axis coefficient and the once-per-rev parameters) are roughly appropriate for SOPAC or IGS orbits since late 1994.  The orbital constraints to be applied are one of most important decisions you have to make in setting up the analysis.  In deciding upon constraints, remember that SOLVE will perform two sets of solutions—one ("constrained" or "tight") which uses directly the input constraints and one ("loose") which uses hard-wired, loose constraints (10 ppm).  The "tight" solution is displayed in the Q-file, used for updating the L- (station-coordinate) and G- (orbital parameter) files and for writing the M-file of parameter adjustments that is used for scanning and manually editing the post-fit residuals.  If you are not using GLOBK, this GAMIT-produced "tight" solution provides the final estimates of parameters.  The "loose" solution is not displayed in the Q-file (except for its constraints and statistics, at the bottom), but is written into the H-file for input to GLOBK.  If you are using GLOBK for your final analysis, you set the orbital (and station) constraints there, and the GAMIT sestbl. values have no direct effect on the GLOBK solution.  They can have an important indirect effect, however, since resolution of phase ambiguities ("bias-fixing") is performed by SOLVE as part of the constained solution, with the resolved integer values carried forward to the loose solution.  So in deciding what values to use in the sestbl. for orbital constraints, you need to consider both the expected accuracy of your a priori orbit and the strategy you plan to use for your analysis.  Moreover, you will probably want to perform several different analyses, using chi-square, coordinate uncertainties, and  success in resolving ambiguities to determine the optimal value of the orbital constraints for the GAMIT solution.  See section 5.5 below and also Feigl et al. [1993] for further discussion.

The three command lines beginning with Type of Analysis should be considered together in formulating your plan for the analysis.  If you have good a priori coordinates (see Chapter 4.2) and orbits, you can perform the GAMIT analysis in a single sequence  using the following sestbl. commands:

Type of Analysis = 0-ITER
Choice of Observable = LC_HELP
Choice of Experiment = RELAX
Data Status = RAW

This will result in the generation of pre-fit O-C's by MODEL, automatic editing and repair of cycle slips by AUTCLN, and a solution in which SOLVE will attempt to resolve phase ambiguities for regional stations.  With good a priori orbits, you will probably find your processing most efficient to use 0-ITER even when you have a few stations with poorly known coordinates:  updating the L-file from the first solution and repeating the (0-iteration) run will be faster than performing multiple complete iterations.  

If you need to iterate either the coordinates or orbital parameters (assuming your network is sufficiently large to improve the orbit), then you should use Type of Analysis = 1-ITER. With this command, there will an additional sequence of MODEL, AUTCLN, SOLVE, and (optionally) ARC to improve the coordinates (and possibly orbit) prior to the final solution. The initial solution will be performed using the "quick" algorithm, in which SOLVE estimates (implicitly) an extra bias parameter at each gap or flagged (by AUTCLN) point in the double-difference observations, rendering the parameter estimates less accurate but also less sensitive to cycle slips.  A quick solution will usually remove all systematic trends in the residuals, allowing for relatively easy repair of any remaining small cycle slips, either automatically by AUTCLN or manually using CVIEW.  The "regular" (i.e., not "quick") solution by SOLVE inserts extra bias flags only when flagged by AUTCLN.

Choice of Observable = LC_HELP means that the observable is the ionosphere-free linear combination ("LC" or "L3") and that the regular SOLVE solution attempts to resolve phase ambiguities using both an ionospheric constraint and pseudorange data if available.  For networks extending over less than a few kilometers, you can set  Choice of Observable = L1,L2_INDEPEND to use the L1 and L2 phase observations directly, which will result in smaller measurement noise as long as the ionsopheric contribution is negligible.  

Choice of Experiment = RELAX means that you are solving for both station coordinates and orbital parameters, a reasonable approach even for short-range networks provided you apply appropriate constraints to the orbital parameters.  You can suppress orbital parameters completely by setting Choice of Experiment = BASELINE.

If you have data that have been previously cleaned (and saved in the form of X-files written using program CTOX), you should set  Data Status = CLN to avoid running AUTCLN.  

Initial ARC determines whether or not ARC is run as the first step in your batch processing.  If you have a T-file from earlier analyses or from running sh_sp3fit, you do not need to regenerate it in your data processing.  If on the other hand you have only a G-file (from SOPAC or earlier as the output of earlier analyses), you should set  Initial ARC = YES.

Inertial frame establishes the inertial coordinate system for the orbital integration in ARC, the orbital ephemerides themselves (T-file), and the calculation of the theoretical observable in MODEL.  In a fundamental sense the frame is arbitrary; as long as you transform coordinates and ephemerides consistently between the Earth-fixed and inertial frames, the choicer of inertial frame matters only if you are combining inertial orbital parameters with those from an external source.  The current convention for astronomical and IGS use is the equator and equinox of Julian epoch 2000.0, designated J2000 and corresponding to 0h UTC on 1 January, 2000. If you plan to use G- or T-files from SOPAC and/or you are starting anew in you processing and want to be consistent with the rest of the world, you should specify J2000, which is the current GAMIT default.  The default for releases 9.4 or earlier was 'B1950', designating Bessilian epoch 1950.0.  You should specify this if you wish to repeat a solution you have previously run.  If you specify J2000 but have a B1950 G-file (or vice versa), ARC will automatically convert the G-file before integrating, saving the old file with an additional extent (.B1950 or .J2000). 

AUTCLN Command file allows you to input controls for AUTCLN.  Although the default options are often adequate, creating the command file is a useful way of documenting the editing parameters and allows you to inject manual edits (see Section 6.2). 

The most appropriate way of handling the atmosphere depends on the size of the network and the accuracy desired.  For networks less than a few kilometers in extent, the atmospheric delay effectively cancels between stations, so you do not want to estimate any atmospheric parameters. For larger networks, you should estimate one or more zenith delay parameters for each station ( Zenith Delay Estimation = Y).  The zenith delay parameters for regional stations will be highly correlated, but there is sufficient precision in the estimation algorithm that these high correlations will not degrade your estimates of station coordinates and the differences in zenith delay between stations will be well determined.  (If you wish to see in the output the uncertainty of the differences, then you can add tight constraints to one of the zenith delays in the SOLVE batch file;  see Section 7.5).  The default is to estimate a single zenith delay for each station with an a priori constraint of 0.5 meters.  You may allow a variation in the zenith delay during the observation span by specifying a piecewise-linear model with stochastic constraints.  Number Zen is the number of "knots" in the model; hence, for a new value every 3 hrs of a 24-hr session, you would set  Number Zen = 9.  A knot spacing between 1 and 4 hours is reasonable for most situations, the trade off being resolution versus program size and run time.  The allowed variation between tabular points in the estimation is defined by a Gauss-Markov process with a default value of  0.02 m / ÷ hr.   The default correlation time is set to 100 hr, making the process effectively a random walk.  Specification of these parameters is documented in Table 5.1 and discussed further in Section 8.3.  A new feature with release 9.58 is the ability to estimate a north-south and an east-west gradient in atmospheric delay, given as the differences in meters at 10 degrees elevation  (see Section 8.4).  The final entry for atmospheric modeling is the minimum elevation angle for accepting observations.  In the presence of modeling deficiencies for the atmospheric delay or the phase-center variations of the antenna, estimated station heights can be quite sensitive to this cutoff angle.  

Antenna Model refers to the use an elevation-dependent or elevation-and-azimuth-dependent model for the effective phase center of the receiver antenna.  The default is to use no model, but the IGS has recently (July 1996) adopted a set of elevation-dependent models for the most commonly used antennas.  To invoke the IGS models, you should use a version of the antmod.dat table which incorporates them and specify Antenna Model = ELEV in the sestbl. (or equivalently, for each station in the sittbl.—see below).   

By default corrections to Earth rotation parameters  are estimated for each session (Estimate EOP = 15).  If your solution includes 24-hr tracking from a global set of stations, then you can estimate well pole ("wobble") position and UT1 rate but not a UT1 offset since this is perfectly correlated with the nodes of the satellites' orbits.  In order to have a full convariance matrix available for GLOBK, however, it is preferable (and necessary in versions prior to January, 1995) to turn on all six EOPs but with tight constraints on the UT1 offset in the GAMIT solution.  The default constraints for UT1 rate and pole position and rate are rather loose, so these should be tightened to match the uncertainty in your a priori tables (~ 0.0001 sec/day, 0.001 arcsec, 0.0005 arc/day for IERS Bulletin A or B finals) if you have only a regional network and want to assess carefully the results of the GAMIT analysis.  

The final set of the sestbl. inputs shown control resolution of phase ambiguities in the solution.  Unfortunately, no GPS analysis group or software package (to our knowledge) has automated ambiguity resolution to the point where you can uncritically apply a particular algorithm to all situations.  GAMIT uses a combination of pseudo-range observations, if available, and phase observations with an ionospheric constraint to provide flexibility and redundancy.  This approach, together with some fairly conservative threshhold criteria makes the process reasonably but not perfectly failsafe for most networks.  Tuning the algorithm for your particular network and evaluating the results is discussed in Section 5.5. 

There are a number of optional entries in the sestbl. that may be invoked for special cases and to excercise greater control over the processing.  These are summarized in Table 5.1 and further discussed below.

Table 5.1   Summary of sestbl. entries  
_____________________________________________________________________________________________

Processing Agency	|    Required —
Station Number	|	see discussion
Satellite Number 	|	above
Station Constraint 	|
Satellite Constraint	|

  Analysis controls

Type of Analysis 	0-ITER:  ARC (optional), MODEL, AUTCLN (optional), SOLVE, SCANDD 
	1-ITER:  Two sequences of 0-ITER, the first using "Quick" SOLVE
	2-ITER:  Three sequences
	PREFIT:  0-ITER but without SOLVE
	QUICK:   0-ITER but with "Quick" SOLVE
SOLVE-only = YES	YES/NO  default = NO 

Data Status	RAW:     Include AUTCLN before each SOLVE run
	CLEAN:   Do not include AUTCLN in the processing sequence

Choice of Observable	LC_HELP: Ambiguity-free and ambiguity-fixed solutions with LC
	LC_RANGE: Same as LC_HELP but with pseudo-range priority
	LC_ONLY: Ambiguity-free solution with LC
	L1_ONLY: Ambiguity-free and ambiguity-fixed solutions with L1 
	L2_ONLY: Ambiguity-free and ambiguity-fixed solutions with L2
	L1,L2_INDEPEND:  Ambiguity free and fixed solutions with L1 & L2
	L1&L2:   (see notes below)

Choice of Experiment 	RELAX:  Include station, orbital, and Earth-rotation parameters
	BASELINE: Do not include orbital or EOP paramters

  Data weighting

Station Error 	UNIFORM [sigma] : Weight all phase data equally, 
			[sigma] = 1-way L1 or L2 in mm, default = 10.
	BASELINE [a] [b] : Weight proportional to baseline length
						    a**2 + (b**2)(L**2) im mm, ppm, def 10. 0.
				ELEVATION [a] [b] [elev] : Weight by elevation angle; 1-way  					a**2 + b**2/sin(elev)**2 in mm, deg; def= 4.3 7.(
Satellite Error 		UNIFORM [sigma] : Satellite error added quadratically to station 						       error; default = 0.

  Ambiguity Resolution

Ionospheric Constraints	0.0 mm + 1.00 ppm  [see below and Section 5.5]
Ambiguity resolution WL	default = 0.15 0.15 1000. 10. 500.  [see below]
Ambiguity resolution NL    default = 0.15 0.15 1000. 10. 500.  [see below]
Type of Biases		EXPLICIT  Necessary for ambiguity resolution (default) 
				IMPLICIT  Default for Quick solution

  Atmospheric Parameters

Zenith Delay Estimation	Yes/No  to estimate zenith delay parameters; default = No
Elevation Cutoff	Give value in degrees; applied in SOLVE;  default  = 15.          Number Zen	Number of zenith-delay parameters per station; default = 1
Zenith Model	PWL: Piecewise-linear ( default for Number Zen > 1 )
	CON: Constant from time of knot (i.e., step model)
Zenith Constraints	Overall a priori constraint in m; default = 0.5
Zenith Variation 	[var] [tau] : Variation and correlation parameters in Gauss 	   	          Markov model; default =  0.02 m/sqrt(hr) and 100 hrs.
Atmospheric Gradients	Yes/No to estimate a N-S and E-W gradient; default = No
Gradient Constraints	Gradient at 10 deg elevation in meters; default = 0.03 m
Tropospheric Constraints	YES/NO: Spatial constraints, default = No (see Sec 8.3)

  Orbit parameters

Initial ARC			YES: Integrate G-file ICs to get a T-file (default for RELAX)
				NO:  Use existing T-file (default for BASELINE)
Final ARC			YES: Re-integrate the final estimated ICs
				NO:  Suppress  re-integration of the final estimated ICs (default)
Inertial frame		J2000: T-file & calculations in J2000 (default & current SOPAC)
				B1950: Old T-file and SOPAC frame
Radiation Model for ARC 	BERNE: 9-parameter model (GAMIT and SOPAC default) 
				SPHRC: 3-parameter model (old GAMIT and SOPAC default)
				SRDYB: 
				SVBDY:  
Reference System for ARC	IGS92: Gravitational constants from IGS 1992 standards (default)
				WGS84: Gravitational constants from WGS84 standards (BC ephemeris)
Tabular interval for ARC	Output interval on T-file in seconds; default = 900.
Stepsize for ARC		Integration stepsize in seconds;  default = 75. 
Export Orbits	YES/NO: Create or not an Earth-fixed SP3 file for export (def = No)
  Orbit id 	4-char code for export orbit
  Orbit Format 	SP1/SP3 (NGS Standard Products), default = SP3
  Orbit organization 	3-char code for processing agency for export orbits
  Reference System for Orb	5-char code for Earth-fixed reference system for export orbits

  MODEL parameters

Antenna Model 		NONE: No model for phase-center variations (default)
				ELEV: Elevation-dependent model in antmod.dat.
				AZEL: Elevation- and azimuth-dependenet model in antmod.dat
Tide Model 			Binary coded: 1 earth  2 freq-dep  4 pole  8 ocean   default = 3 
Earth Rotation		Diurnal/Semidirunal terms: Binary coded: 1=pole 2=UT1 default=3
Yaw Model			SV yaw used from svnav.dat; YES/NO  default = YES
Use I-file			Reference clock polynomial; YES/NO  default = YES

  SOLVE parameters

Estimate EOP 		Binary coded: 1 wob  2 ut1  4 wob rate  8 UT1 rate; default 15 
Wobble Constraint		[pole] [pole rate]  default = 3. 0.3  (arcsec) (arcsec/day)
UT1 Constraint		[UT1] [UT1 rate]    default = 0.00002 0.02 (sec)  (sec/day)
Select Epochs		[start] [stop]  
Decimation Factor 		[factor]   Default = 1  (no decimation)
H-file solutions 	LOOSE-ONLY:  Write only the loose solutions on the H-file (default)
	ALL:   Write both the constrained and loose solutions on the H-file

  Cleaning parameters

Clean Option 		AUTCLN:  Use kf program AUTCLN for cleaning (default)
				SINCLN:  Use GAMIT program SINCLN 
				DBLCLN:  Use GAMIT programs SINCLN plus DBLCLN
AUTCLN Command File		[filename]   Default none (use default options in AUTCLN)
Edit AUTCLN Command File	Add delete commands to autcln.cmd for bad clocks YES/NO default = NO
Delete eclipse data		POST:  Add delete commands for 30 min after eclipse (default)
	 			ALL:   Add delete commands for eclipse and post-eclipse
Iteration	XFILES:  On iteration, run AUTCLN on original data (default)
	CFILES:  On iteration, run AUTCLN on previously cleaned data
				NO:    Do not delete data during or after eclipse.
SCANDD control		BOTH:  Run SCANDD after each solution (default)
				IFBAD: Run SCANDD only if the nrms > 1.0
				FIRST: Run SCANDD only after the quick solution
				FULL:  Run SCANDD only after the full solution
				NONE:  Do not run SCANDD at all.

  File handling

X-compress = YES 	Uncompress/compress X-files  default = NO 
Delete all input C-files	YES/NO  default = NO
Delete MODEL input C-files	YES/NO  default = NO
Delete SINCLN input C-files	YES/NO  default = NO
Delete DBLCLN input C-files	YES/NO  default = NO 
Delete AUTCLN input C-files	YES/NO  default = NO 
Update T/L files	T_AND_L (default), T_ONLY, L_ONLY, NONE 
                                (Applies only to update for full solution after quick)
Run CTOX = YES	Make clean X-files from C-files  default = NO

Analysis controls.  The Type of Analysis, as discussed above, is almost always 0-ITER or 1-ITER.  The most common use of 2-ITER would be in determining orbits, where high correlations require multiple iterations to achieve convergence.  PREFIT will generate batch files for ARC, MODEL, and AUTCLN, but not CFMRG or SOLVE.  It is a convenient way to generate C-files for inspection with CVIEW, trial editing with AUTCLN, or for input to MAKEJ when you have mismatched time tags in the presence of SA.  QUICK will generate the standard 0-ITER sequence but set SOLVE for a "quick" solution.  A separate command, SOLVE-only, allows you to set up a batch run from C-files, executing only CFMRG and SOLVE.  As discussed above, Data Status determines whether AUTCLN (or SINCLN/DLBCLN) is included in the run.  Among the Choice of Observable selections, the only one not already explained is L1&L2.  With this choice ambiguities are resolved simultaneously for L1 and L2 (as in the L1,L2_INDEPEND option) but with an ionospheric constraint which remains in the final solution.  This option has not been recently tested and so should be used with caution.  Choice of Experiment is discussed above. 

Data weighting.  For analysts who wish to experiment with non-uniform weighting of the phase data, several options are available.  If you are not estimating orbital parameters and expect a non-negligible contribution from orbital errors, you may wish to weight the observations according to baseline length, as described by Bock et al. [1986] —see Chapter 1 for references].  In this case you specify Station error = BASELINE a b, where a is the constant component in mm and b the baseline-length component in parts per million; the two terms are combined quadratically.   A second (and mutually exclusive) approach is to assign  errors according to elevation angle:  Station error = ELEVATION a b, where a is again a constant and b2 multiplies a term inversely proportional the sine of the elevation angle.  The default values (4.3 and 7. ) are chosen (rather arbitrarily) such that an observation at 40∞ (the median elevation of a typical session at mid-latitudes) has the same weight as with UNIFORM option with the one-way L1 sigma equal to 10 mm, and an observation at 20∞ has half the weight.   This option can be invoked on a station-by-station basis by editing the SOLVE batch file (see Section 7.5) but can only be invoked uniformly for all stations from the sestbl.  With any of the three station-weight options, you can specify an additional term by which a particular satellite's observations can be downweighted.  Set Satellite error = UNIFORM a, where a is a constant  in mm to be added quadratically to the station error. 

Ambiguity resolution.  These inputs allow you signficant control over the criteria used to resolve phase ambiguities.  Ionospheric Constraints specifies the constraint applied to the ionosphere in estimating the wide-lane (L2–L1) phase ambiguity.  In this input, unlike most of the others in the sestbl., you must follow the format to the right of the = sign exactly.  The two Ambiguity resolution entries specify the decision-function and chi-square search parameters to be used for widelane (WL) and narrow-lane (NL) resolution.  The fourth parameter is the maximum baseline length (in km) over which you want to attempt to resolve ambiguities.  Strategies for choosing these parameters are discussed in Section 5.5.  The Type of Biases entry specifies whether ambiguity parameters are carried through explicitly or solved for implicitly.  Selecting IMPLICIT reduces the size of the SOLVE output (Q-) file but precludes resolving ambiguities. 

Atmospheric parameters.  Most of the entries for this group were explained in the standard setup.  The only additional entry is Tropospheric Constraints, which allows you to assume a spatial correlation among zenith delay parameters using the structure function described by Treuhaft and Lanyi [1986] (see Section 8.6).  We have tested this constraint in only a limited way (with slightly positive results).  It is currently coded only for a single zenith-delay parameter per station.

Orbit parameters.  The first two entries control whether or not ARC is run to create a T-file prior to the first MODEL run (Initial ARC) and after the final SOLVE (Final ARC).  As indicated above, you may surpress the initial integration if you already have a T-file.  You do not need to create a T-file from the estimated orbital parameters unless you need it for further processing or wish to create an SP3 file for export.  The next entry sets the inertial frame of the G- and T-file, as described above.  The next two entries specify the dynamical model to be used in the integration of initial conditions.  The default gravitational field (Reference system for ARC = IGS92) is from the IGS/IERS 1992 standards (see McCarthy [1992] in the references in Chapter 2), but you can specify the WGS84 field if you wish to perform comparisons with a DoD orbit.  There are two commonly used models for non-gravitational ("radiation pressure") accelerations on the satellites.  Prior to mid-1995, GAMIT and SOPAC orbits were generated with "spherical" or "flat-plate" model that had three adjustable parameters:  coefficients representing a "direct" (Sun-facing), "y-bias" (along the spacecraft y-axis), and "z" (along the Earth-facing spacecraft axis) accelerations.  A more comprehensive and demonstrably better model uses 9 adjustable parameters including both constant and once-per-revolution accelerations (as described by Colombo [1986]).  The particular form of this model we employ is close to that described by Beutler et al. [1994] and hence is designated BERNE.  These and two other models available are described in Section 7.2.  The last two entries in this group control the integration stepsize and T-file tabular interval.  The default from release 9.2 forward is a 75-second stepsize and 900-second (15-minute) tabular interval.  These are reduced from the former 168-second and 1350-second (22.5-minute) intervals to provide consistency with IGS standards.  There are differences between a 75-second and 168-second integration stepsize for eclipsing satellites—up to 20 cm over 1 day (±12 hrs from a midpoint epoch) and up to 60 cm over 3 days.  The differences (errors) for some eclipsing satellites in the 75-second integration compared with one with a 150-second stepsize are less than 5 cm over 1 day but up to 30 cm over 3 days.  The tabular spacing can remain at 15 minutes for these smaller stepsizes providing the former is an integer multiple of the latter.  The final group of entries are used if you wish to create an NGS SP#1 or SP#3 format ephemeris file from the final ARC integration (done routinely at SOPAC processing but rarely elsewhere).  The 4-character Orbit id gets used in the export file name.  The Orbit organization and Reference system for Orb are written onto the header of the file (see the SP#1 and SP#3 format descriptions).  Since these are Earth-fixed orbits, the reference system refers to the terrestrial frame used to define the station coordinates in the GAMIT or GLOBK solution (e.g. ITR94 for ITRF94).

MODEL parameters.  Besides the antennas phase-center model (Antenna model), discussed above, there are controls to specify the model used for solid-Earth tides, Earth rotation, satellite yaw, and receiver clocks.  Tide Model is binary coded to allow inclusion of constant-Love-number tides ("1" bit), the frequency-dependent (K1) radial tide ("2" bit), pole tides ("4" bit), and ocean-loading effects ("8" bit), all modeled according to IGS 1992 standards.  The default (= 3) is to include the direct solid-Earth tide, including the frequency-dependent term.  We have not been able to demonstrate any improvement using the pole tide, and we do not yet have ocean-tide components for a sufficient number of stations to include these in the model.  Earth Rotation allows you to disable the addition of diurnal and semi-diurnal terms to the UT1 and pole angles read from tables.  The default is to include them.  Yaw Model allows you to disable modelling of satellite yaw (rotation of the antenna away from the Earth-pointing position).  Finally, you have the option (Use I-file) of not including in the theoretical observable a piece-wise polynomial model of the station clock, computed by FIXDRV from the K-file samples written into the I-file.  Since the receiver clock rate cancels in double differences (all channels are sampled simultaneously), it does not need to be modeled.  However, using the I-file is recommended to prevent numerical problems which sometimes occur in SOLVE if there is a large station clock drift and a long gap in the data from a satellite (from its setting and then rising again).  The only time you might want to omit the I-file is if you have inadvertently deleted it or the K-files and don't want to recreate them using MAKEK or MAKEX. 

SOLVE parameters.  Estimation of Earth rotation parameters (Estimate EOP) should be considered in most analyses, as discussed above.  The estimation control is binary coded, with the "1" bit used for pole position, the "2" bit for UT1 offsets, the "4" bit for pole rate, and the "8" bit for UT1 rate.  The units of the a priori constraint are arcseconds and arcseconds per day for pole and (time) seconds and (time) seconds per day for UT1.  By default, corrections to the constant and rate of UT1 and pole position are estimated for each session (Estimate EOP = 15) but you may want to tighten the constraints if you have only regional data in your analysis.  The two remaining commands for SOLVE allow you to use only part of the data, either for sensitivity tests or to reduce the run time.  To use a partial span, enter the stop and start epoch numbers (determined from the X-file or using CVIEW) after Select epochs = .  To use only every nth point set Decimation factor = n.   These two controls may be used together.  H-file solutions controls what solutions are written into the H-file  for use by GLOBK.  The default is now to write only the two (biases free and biases-fixed) loosely constrained solutions, not the solutions produced by the input GAMIT constraints, in order to reduce the size of the H-files.  If you need to have the constrained solutions in the H-file (e.g., for debugging or post-processing with FONDA), then you should specify  H-file solutions = ALL.

Cleaning parameters.  There are four controls for cleaning the data.  Clean Option specifies what programs are used:  SINCLN only  (SINCLN) or SINCLN+DBLCLN (DBLCLN) from the GAMIT directories or AUTCLN from the GLOBK (kf) directories. Although some analysis groups have found SINCLN, at least, still helpful in getting a first cut at a difficult data set, AUTCLN is recommended and should work better than the GAMIT programs in all cases if you have good a priori coordinates and orbits.   AUTCLN Command File allows you to input the name of command file for AUTCLN (recommended); the usual name is autcln.cmd.  Edit AUTCLN Command File = YES will invoke the shell script avedit to extract messages about clock errors from the P-file created by MODEL and to add commands to autcln.cmd to delete these data in cleaning. There are three options for handling eclipse data, implemented by edits written into the AUTCLN command file.  The default is Delete eclipse data = POST, which will unweight observations occuring during the first half-hour following an eclipse, the period during which the yaw model always fails.  ALL will unweight data during the eclipse as well, and NO will keep all of the data. The Iteration command controls whether the second MODEL/AUTCLN sequence in a 1-ITER or 2-ITER run uses the original X-files (default) or the C-file created from the last run.  Finally, since a SCANDD run is one of the most time-consuming parts of the processing and may be useful only at the end, and then only when the normalized rms from SOLVE suggests the presence of cycle slips, SCANDD control allows you to specify when in the batch sequence SCANDD gets executed.  For unclean data, FIXDRV always writes a line for SCANDD into the batch file after each solution, but SCANDD control determines whether or not it is dummied by a comment character (#).  With SCANDD control = BOTH (the default), SCANDD will be executed unconditionally after the quick and full solutions.  Option FIRST causes execution after the quick solution only, FULL after the full solution only, and NONE after neither.  Option IFBAD will write into the batch file csh commands to look at the normalized rms in the Q-file; only if the nrms is greater than 1.0 will SCANDD be run. 

File handling.  These entries allow you some control over the files used or created in your batch run, and hence the amount of disk space required to process a survey.  If X-compress = yes, then the batch script will expect the X-files to be compressed at the beginning of the run and will compress them again at the end.  The next group of entries allows you to delete the input C-files from one or more processing steps.  The default is to save all C-files so that you check the editing for each interation.  At the other extreme, setting Delete all input C-files = yes will assure that no more than two sets of C-files are resident at the same time and will leave only the last set on the disk at the end.  Finally Run CTOX = yes creates at the end of the run a set of X-files with cleaned data, allowing you in principal to delete the last set of C-files if you have no further need to re-run SOLVE with different constraints or to examine the post-fit residuals with SCANDD or CVIEW.  The correctly edited data on these X-files can be used as subsequent inputs to GAMIT processing with Data status = clean. 

The form of the site control table ( sittbl. ) is shown below.  The columns occupied by each entry are indicated by the keywords and dashes at the top of the file, and since these are used to read the entries, the order is arbitrary.  Most of the entries are also optional, with the required information picked up from defaults or from corresponding (station-independent) entries in the sestbl.  The example below shows the most commonly used entries; the omitted ones specify the atmospheric models and are described in Chapter 8.

STATION              FIX  --COORD.CONSTR.-  --EPOCH--  CUTOFF  CLK  KLOCK  CLKFT APHS
CATO Castro Peak  NNN  100.  100.  100.   001-  *    10.0   NNN     3         NONE
LOVE Loma Verde   NNN  100.  100.  100.   001-  *    10.0   NNN     3         NONE
PVER PVER7268     NNN  0.01  0.01  0.01   001-  *    10.0   NNN     3         NONE
SAFE San Fernando NNN  100.  100.  100.   001-  *    10.0   NNN     3         NONE
WSFD WSFD GPS     NNN  0.01  0.01  0.01   001-  *    10.0   NNN     3    L    NONE
YKNF YELLOWKNIFE  NNN  0.01  0.01  0.01   001-  *    10.0   NNN     3    L    NONE
AROG ARO GPS      NNN  5.00  5.00  5.00   001-  *    10.0   NNN     3    L    NONE
RICH RICHFRPA     NNN  0.05  0.05  0.10   001-  *    10.0   NNN     3    L    ELEV 
TROM TROMGPSM     YYY  5.00  5.00  5.00   001-  *    10.0   NNN     3    L    AZEL  
TSUK TSUKMMAC     DDD  5.00  5.00  5.00   001-  *    10.0   NNN     1         NONE

The table may contain any number of stations, whether used in the experiment or not.  The 4-letter code must match that used in the D-file; the 12-letter descriptor is arbitrary and not used (the full station names for the q-file are read from station.info).  The third column (in the example shown) indicates which, if any, of the three station coordinates are to be fixed/free (Y/N) in the solution, or ignored (D).  Ignored stations include those that do not appear in the D-file but are listed in this table only for convenience.  Deleting the data from a station that appears in the D-file done must be done by using the exclude command, inserted into SOLVE batch file (see Section 7.5).  Any a priori coordinate constraints  are given under COORD.CONSTR. in units of meters for latitude, longitude, and radius.  Whether one uses coordinate constraints or not is specified in sestbl. (as described earlier).  You should think carefully about this entry since this is your opportunity to define the reference system for the analysis by constraining the coordinates of one or more fiducial stations.  If you plan to use GLOBK for your final analysis, you should avoid absolute fixing of any stations, but rather use a priori constraints.

You can restrict the number of observations to be used from one or more stations by specifying a range of epochs ( EPOCH ) or changing the elevation cutoff ( CUTOFF ). In the current version of the software any modifications to EPOCH or CUTOFF will apply globally to all sessions.

The next three entries control the way the receiver clock is handled.  The CLK entry indicates whether or not an offset, rate, or acceleration term is to be estimated by SOLVE.  Almost always the answer is "No" ( N ).  KLOCK selects the way the clocks are modeled and can be quite important for certain receivers.  For all receivers except MiniMacs you should normally select option 3 to indicate that the receiver clock offset is to be estimated epoch-by-epoch using the pseudorange (see Section 4.9), and that the effect of oscillator variations on the phase is to be modeled with a low-order polynomial.  Since the MiniMac receivers keep their clocks synchronized with the GPS satellites, it is preferable to assume an offset of 0. by selecting option 1.  The third option ( 2 ) uses the low-order polynomial for both the epoch offset and oscillator variations.  This approach will model receiver clock offsets as well as will Option 3 if the receiver clock stability is sufficient (better than ~ 10-8) to keep deviations from the polynomial less than 1 microsecond throughout the observation span.  The crystals in the TI 4100 and MACROMETER II usually meet this requirement but those in the newer low-power receivers do not unless they are locked to an external atomic oscillator (as at some IGS tracking stations).  The order of the polynomial to be used by FIXDRV may be specified under CLKFT as linear ( L ) or cubic ( C ), or left for FIXDRV to decide from the fit by leaving this column blank.

The final column shown in the example is for invoking a model for variations in the phase center of the receiving antenna ( APHS ).  The use of a model for all stations can be controlled using the sestbl. entry, but the sittbl. entries override the sestbl. if the former are present.  So to avoid confusion, you may want to omit this column from the sittbl. except for those analyses in which you need to control the model separately for each station. 

The usual way to run FIXDRV is to give the name of the D-file as a command-line argument.  In this case, there are no further prompts necessary.  If an I-file exists, it will be used; if not, it will be created by fitting polynomials to the clock values given in the K-files.  If you wish to choose an alternate I-file, or recreate the I-file even though it exists, you should run FIXDRV interactively by not specifying the D-file as a command-line argument.  In this case, FIXDRV will prompt you for the name of the D-file.  It will then ask what you want to do about the I-file:  use the old one, save the old one and create a new one, or overwrite the old one.  Most of the time you probably want to "Use the old one" (option 3) and avoid a time-consuming recalculation of all the clock coefficients, but if you have added a station to the D-file since last running FIXDRV or have updated the K-file by rerunning MAKEX or MAKEK with improved station coordiantes, you should create a new I-file.

When you run FIXDRV to create an I-file, you will get a display for each station summarizing the quality of the clock-polynomial fit.  If you have not previously checked the K-files using CALCK, as described in Chapter 4, you should make sure that all of the fits are reasonable (rms less than a few tens of microseconds if you are using clock options 1 or 3; less than one microsecond if you are using option 2).

5.3  Executing the Batch Run  

The output of FIXDRV is a command file (shell script) named b{expmt}.bat which invokes the GAMIT modules in the appropriate order for the type of analysis you have requested (see the example on the following page).  To execute the analysis run in foreground type csh {batch file name}; in background type gbat {batch file name}.  (If your system recognizes the batch file as a command file [use chmod +x under UNIX], you can of course omit the csh when running in foreground.)  All of the required modules will then be executed automatically to perform the processing sequence you have defined with FIXDRV.  Beginning with release 9.5, the first lines of the batch file remove any existing files logging the status of the batch run (GAMIT.status) and warnings (GAMIT.warning) or aborts (GAMIT.fatal).  Most messages generated by the GAMIT modules and AUTCLN are now written into these files instead of directly to the screen (or b{expmt}.bat.log if the job was executed using the gbat).  The first code executed by ARC, MODEL, CFMRG, and SOLVE is a check for the existence of GAMIT.fatal; if it's found, indicating that the previous step in the batch sequence has failed, the current module will terminate also.  This feature is designed to avoid the common problem of overlooking the failure of a previous step in evaluating the success of a run.  

For most of the modules, the command references a secondary B-file containing the input stream for one execution of the specified module.  Each input stream contains replies to all the queries that the user would encounter when running the module interactively.  In the case of AUTCLN or SINCLN, there are command-line arguments rather than a secondary batch file given.  For AUTCLN, these arguments are the command file name (optional), a chracter indicating whether input C-files are overwritten (' .') or the 6th character incremented ('+'), and the name of a D-file (to be read for the C-file names) and the 6th character of the input C-files (which may be different from the names in the D-file). (See Chapter 7 for more detail.)  For SINCLN, which may be used instead of AUTCLN, only an input and (optionally) output C-file name is required.  

The sequence of program executions is listed in the primary B-file and the individual responses are listed in the secondary B-files.  An example of a primary B-file for a 1-ITERATION analysis is shown below:

 bvent7.bat
#! /bin/csh
# Remove any existing GAMIT.status, .warning, .fatal files
/bin/rm GAMIT.status
/bin/rm GAMIT.warning
/bin/rm GAMIT.fatal
arc    < bvent7.001
model  < bvent7.002      
model  < bvent7.003      
model  < bvent7.004      
model  < bvent7.005      
model  < bvent7.006      
model  < bvent7.007      
model  < bvent7.008      
autcln autcln.cmd . diter7.278      7 >! autcln.out
mvcf 7 a
cfmrg  < bvent7.009      
solve <  bvent7.010      
set rms = 'grep Pre q????1.??? | awk '$6 > 5 {print 'no'}'`
if ( $rms == "no" ) exit
scandd < bvent7.011      
arc    < bvent7.012      
model  < bvent7.013      
model  < bvent7.014      
model  < bvent7.015      
model  < bvent7.016      
model  < bvent7.017      
model  < bvent7.018      
model  < bvent7.019      
autcln autcln.cmd . diter7.278      a >! autcln.out
mvcf b c
cfmrg  < bvent7.020      
solve <  bvent7.021      
scandd < bvent7.022      
arc    < bvent7.023      

The conditional operation following the first SOLVE checks to see if the normalized rms from the quick solution is large ( > 5.0 – see section 5.4), and if so, terminates the run so that you can examine the AUTCLN or SOLVE output and/or the residuals directly using CVIEW.    Listed below are explanations for each module execution in the 1-ITERATION batch file.

ARC	Generate an orbital ephemeris (T-file) with partials using as initial conditions a G-file produced by BCTOT or copied from SOPAC.  This step can be skipped if you've already created a T-file using sh_sp3_fit or sh_bcfit or copied one from SOPAC.
MODEL	Compute prefit residuals ("O-C's") and partial derivatives for the observations on each X-file; create C-files with the same names (except for the first letter) as the X-files.
AUTCLN	Read the C-files output by MODEL and search for cycle slips and outliers in the pre-fit one-way and double-difference residuals, inserting extra biases at all questionable gaps; create the "a" series C-files (i.e., with the year digit replaced by "a") with these corrections to the phase data and prefit residuals (optionally overwriting the "year" series output by MODEL).
CFMRG	Set up the M-file for the least squares fit:  define and select the parameters to be adjusted and the C-files to be read.
SOLVE	Perform a "quick" least-squares estimate of station coordinates and orbital parameters; update the M-file with the parameter adjustments (in order to edit post-fit residuals);  write the "a" L-file with an adjusted set of coordinates and the "a" G-file with an adjusted set of orbital initial conditions.  The M-file and Q-file from quick solutions are always named with the sixth character "1".
SCANDD	Using the updated M-file to create predicted post-fit"residuals, scan all double-difference combinations to produce a summary of potential cycle slips remaining.
ARC	Generate a new orbital ephemeris (T-file) using the updated initial conditions (G-file) from the solution.
MODEL	Recompute O-C's and partials using the new T-file and C-files.  Create "b" series C-files.
AUTCLN	Re-clean the data using the flatter residuals obtained from the iterated coordinates and orbits.  Output "b" series C-files.
CFMRG	Create a new M-file with the names of the "b" series C-files;  the "regular solution" M-file always has "a" as its sixth character.
SOLVE	Perform a least-squares estimate of station coordinates and orbital parameters, attempting to resolve phase ambiguities if specified by the type of analysis.  This executation of SOLVE will also update the M-file with the parameter adjustments in order to view or edit the post-fit residuals.  It will also write overwrite the  "a" L-file and create a "b" G-file. Like the M-file, the Q-file from the this solution is named with the sixth character "a".
ARC	[ optionally ] Generate a new orbital ephemeris (T-file) using the updated initial conditions (G-file) from the solution.

There are two important principles to remember using batch files to carry out an analysis.  The first is that you often need to exert control over the execution by commenting out (with # signs) certain lines of the primary B-file.  When you execute your initial batch run, you may want to comment all of the command lines after the first SOLVE in order to inspect the quick solution before reintegrating the orbit, re-MODELing the observations, and performing the regular solution.  There are many things—some beyond your control, some you should have caught but didn't—that can cause the quick solution to be bad (see Section 5.4).  Another example of the need to comment command lines is when you have previously run ARC and don't want to repeat the integration at the beginning of the batch solution, or when you want to postpone the final ARC integration until after you have inspected the Q-file from your solution (though both of these controls can be implemented using sestbl. commands).   Finally, if your batch run fails in the middle for any reason, you can comment the command-lines that have executed successfully and continue the run after the interruption. 

The second important principle concerns the naming conventions for the various files.  Of most concern are the C-file names.  FIXDRV will establish a sequence which increments the sixth character each time a new C-file is written.  In the cleaning sequences (QUICK, 1-ITER, or 2-ITER) the C-files written by the first MODEL run will begin with the year number, e.g., "7" for 1987, and the sequence will continue "a", "b", etc.  (With AUTCLN the incrementing is done using  a "+" rather than a "." in the command line if you do not wish to delete the input C-files, or using the mvcf (or copyc) script to rename the files.) If, for example, you choose to by-pass AUTCLN (by commenting the command line) and perform manual editing with CVIEW, then you should request CVIEW to write output C-files with the sixth character incremented (this is an easy and natural procedure—see Chapter 6).  Then you can continue the batch sequence without having to edit the names of the C-files in the secondary B-files for MODEL and CFMRG.   Special rules apply for 0-ITER with clean data runs, in which only one set of new C-files is created.  In order to accommodate multi-session solutions within a single day, the output C-file from MODEL is the same as the input X-file.  Thus if your input X-files are named with 6th character "a" and "p", for example, designating "am" and "pm" sessions, these letters will be retained in the C-file.  The  0-ITER options with clean data (only) also allow for C-files rather than X-files in the D-file; in this case the C-files output by MODEL will be incremented by one letter (e.g. "a" => "b", "p" => "q"). It is partly because of the inherent complicaton of file naming (but also to reduce processing time) that many analysts prefer to use always 0-ITER (no quick solution), just repeating it with updated coordinates or orbits if the a priori values of these are sufficiently bad to cause problems for AUTCLN or adjustments that are outside of the linear range (see the discussion in Section 4.2.  

Table 5.1 below summarizes the assignment of the sixth character and disposition of the C-files for the most common processing sequences:

Table 5.1	6th character and disposition of C-files in batch processing

	Type of Analysis:	QUICK	1-ITER	2-ITER	0-ITER

MODEL	in (X)	yr	yr	yr	[usually yr]
	out	yr	yr	yr	[same as X]
					[incremented if C]

AUTCLN/SINCLN	in	yr	yr	yr	
	out	a	a	a

CFMRG, SOLVE 	in	a	a	a	yr

MODEL	in			a 
	out			b

AUTCLN/DLBLCN	in		a	b
	out		b	c

MODEL	in		b 	c 
	out		c	d

CFMRG, SOLVE			c	d

Finally, we display the contents of the secondary B-files created in our example: 

File BVENT7.001  (ARC)
PRN  3
PRN  6
PRN  9
PRN 11
PRN 12
PRN 13
END
MERIT SPHRC  900.0   75.0
arcout.002
gvent7.002

  87  23 21 37 23.00000
  87   9 16 37 23.00000
Y
tvent7.002

File BVENT7.002  (MODEL)
O		Old X-file format
pvent7.002	Print file
ivent7.002	Station clock polynomial (I-) file
lvent7.002	Coordinate (L-) file
xcato7.002	Input X or C file
ccato7.002	Output C-file
N		Delete input C-file?
tvent7.023	T-file
I		Inertial frame
N		Use W-file?
N		Use Z-file?
jvent7.002	Satellite clock polynomial (J-) file
0  1  3	Geodetic datum / Tide model / SP Earth rotation
15.0 NONE	Elevation angle cutoff / Antenna model
2		Clock model
1013. 25  20.0  50.0	Pressure, temp, humidity
SAAS  SAAS  CFA  CFA	

File bvent7.008   (CFMRG)
BATCH
cato                4 letter station code
love                4 letter station code
moja                4 letter station code
pver                4 letter station code
safe                4 letter station code
wsfd                4 letter station code
yknf                4 letter station code
 
  3  6  8  9 11 12 13     Total PRN Numbers 
ccatoa.278          C-file
clovea.278          C-file
cmojaa.278          C-file
cpvera.278          C-file
csafea.278          C-file
cwsfda.278          C-file
cyknfa.278          C-file
END
EEEEEEE
mvent1.278          M-file
Y                   coordinate partials?
Y                   atmospheric partials? This should be hard wired
  4  4  4  4  4  4  4     Number zenith delay parameters 
Y                   orbital partials?

File bvent7.009   (SOLVE)
=============================================================
*   << key-word-controlled batch file format >>             *
* symbol ":" must exist in command lines as separator       *
* any non-blank character at first column means comment line 
* empty after ":" means comment line too                    *
=============================================================
*
-------------- Part 1 -- Files and Global Controls
 operation mode:    batch
 Q-file name:       qvent1.278      
 H-file mode:       0
 datum code:        0
 M-file name:       mvent1.278      
 quick solution choice:    quick 
 biases:                   implicit
 phase difference options: double difference
 combination mode:         LC_ONLY
    bias search approach:  decision function
    search path:           narrow lane
    search criteria:       0.15    0.15 1000.00   10.00  500.
 start and end epochs:      1  225
 set cutoff_elevation:
  cutoff:  all _sites 15.0
 error model: 
  stn_error: all_sites uniform 10.0
  sat_error: all_sats 0.0
*
-------------- Part 2 -- Parameters
 set parameters:
    estimate:   all_sites all_parameters
    fix:        all_sites clock
    fix:        all_sites grad
    estimate:   all_sats all_parameters
    fix:        all_sats clock radiation
    fix:        global all_parameters
 exit set:
*
-------------- Part 3 -- A priori Constraints
 set apriori constraints:
    tight_apr_coord:  cato 100.000 100.000 100.000
    tight_apr_coord:  love 100.000 100.000 100.000
    tight_apr_coord:  moja 100.000 100.000 100.000
    tight_apr_coord:  pver   0.010   0.010   0.010
    tight_apr_coord:  safe 100.000 100.000 100.000
    tight_apr_coord:  wsfd   0.010   0.010   0.010
    tight_apr_coord:  yknf   0.010   0.010   0.010
    loose_apr_coord:  all_ 100. 100. 100.
    zenith delays: all_sites  4 PWL
    tight_apr_zenith:  cato 0.500  0.005  100.0
    loose_apr_zenith:  cato 0.500  0.005  100.0
    tight_apr_zenith:  love 0.500  0.005  100.0
    loose_apr_zenith:  love 0.500  0.005  100.0
    tight_apr_zenith:  moja 0.500  0.020  100.0
    loose_apr_zenith:  moja 0.500  0.020  100.0
    tight_apr_zenith:  pver 0.500  0.020  100.0
    loose_apr_zenith:  pver 0.500  0.020  100.0
    tight_apr_zenith:  safe 0.500  0.020  100.0
    loose_apr_zenith:  safe 0.500  0.020  100.0
    tight_apr_zenith:  wsfd 0.500  0.020  100.0
    loose_apr_zenith:  wsfd 0.500  0.020  100.0
    tight_apr_zenith:  yknf 0.500  0.020  100.0
    loose_apr_zenith:  yknf 0.500  0.020  100.0
    tight_apr_grad:  cato 0.030  0.030
    loose_apr_grad:  cato 0.030  0.030
    tight_apr_grad:  love 0.030  0.030
    loose_apr_grad:  love 0.030  0.030
    tight_apr_grad:  moja 0.030  0.030
    loose_apr_grad:  moja 0.030  0.030
    tight_apr_grad:  pver 0.030  0.030
    loose_apr_grad:  pver 0.030  0.030
    tight_apr_grad:  safe 0.030  0.030
    loose_apr_grad:  safe 0.030  0.030
    tight_apr_grad:  wsfd 0.030  0.030
    loose_apr_grad:  wsfd 0.030  0.030
    tight_apr_grad:  yknf 0.030  0.030
    loose_apr_grad:  yknf 0.030  0.030

*      units are ppm for elements, percent for rad parms  (The next two lines are truncated  here by page width )
    tight_apr_orbit: all_ 1.0E+04 1.0E+04 1.0E+04 1.0E+04 1.0E+04 1.0E+04 1.E-03 1.E-03 1.E-03 . .
    loose_apr_orbit: all_ 10. 10. 10. 10. 10. 10. 1000. 1000. 1000. 1000. 1000. 1000. 1000. ..
 exit set:
*
---------------Part 4 -- Session Options
 set session_1 options:
    include:       all_sites all_sats
    atmosphere constraint:     N
    ionosphere constraint:     0.0  1.0
    wide lane ambiguity criteria:   0.15  0.15  1000.0 10.00  500.
 exit set:
*
-------------- Part 5 -- Solution Options
 set tight_free solution option:
    print out solution:    q-file ofile
    print out solution:    q-file ofile
    update file option:    m-file l-file g-file
    input_m file name:     mvent1.278      
    output_m file name:    mvent1.278      
    input_l file name:     lvent7.278      
    output_l file name:    lventa.278      
 set tight_fix solution option:
    print out solution:    q-file ofile
    update file option:    m-file l-file g-file
    input_m file name:     mvent1.278      
    output_m file name:    mvent1.278      
    input_l file name:     lvent7.278      
    output_l file name:    lventa.278      
    input_g file name:     gvent7.278      
    output_g file name:    gventa.278      
    g_line:  By FIXDRV         qventa.278      rwk       12/22/1993  17:07:50               
 set loose_free solution option:
    update file option: 
 exit set:
 set loose_fix solution option:
    print out solution: 
 exit set:

5.4  Evaluating the Quick Solution

The "quick" analysis of a single day's data is not designed to produce the "best" estimates of baseline coordinates, but rather to determine 1) whether there are adequate data to perform a reasonable estimate, and 2) whether the data fit the model to their noise level.  The primary indicator that the first criterion has been met is the magnitude of the uncertainties of the baseline components.  For the second criterion, the primary indicator is the "normalized rms (nrms)" of the solution; i.e., the square root of chi-square per degree of freedom.  If the data were randomly distributed and the a priori weights were correct, the nrms would be close to unity.   In practice with the default weighting scheme, a good quick solution usually produces a nrms of about 0.3.  Anything larger than 0.5 means that there are cycle slips that have not been removed or associated with extra bias parameters (see Sections 2.1 and 6.1), or that there is a serious modeling problem (e.g., bad coordinates of the fixed stations or an unmodeled satellite "burn").

You can evaluate the quality of the solution by examining the Q-file.  We use as an example an analysis of data obtained from a 7-station network in North America on day 278 of 1987.  In this solution the coordinates of three fiducial stations (Palos Verdes, Yellowknife, and Westford) were given a priori constraints of 10 mm. 

          Program SOLVE Version 9.33 of 93/12/20 15:00:00 (apollo)

 SOLVE Run on 1993/12/21  10:58:10
 OPERATOR : rwk             

 Geocentric Coordinates Option

  Quick algorithm
  Ionospheric corrected observations (LC)
  Assumed standard deviation of measurement error:
   Constant term:    10.0 mm   Distance term:  0.00 ppm

 Tracking stations:
  1..  Castro Peak
  2..  Loma Verde P
  3..  MOJAVE GPS  
  4..  PVER7268    
  5..  San Fernando
  6..  WSFD GPS    
  7..  YELLOWKNIFE 

 Satellites observed:
  1..  PRN  3
  2..  PRN  6
  3..  PRN  8
  4..  PRN  9
  5..  PRN 11
  6..  PRN 12
  7..  PRN 13

    A priori coordinate errors in meters
Station    Latitude  Longitude  Radius

  1       100.000    100.000    100.000
  2       100.000    100.000    100.000
  3       100.000    100.000    100.000
  4         0.010      0.010      0.010
  5       100.000    100.000    100.000
  6         0.010      0.010      0.010
  7         0.010      0.010      0.010

   A priori zenith delay     Model = PWL
Station  ZEN_APR (m)   ZEN_VAR (m/sqrt(hr))  Correlation time (hrs)  # of delays

  1         0.500       0.005                     100.0.                 4
  2         0.500       0.005                     100.0                  4
  3         0.500       0.020                     100.0                  4
  4         0.500       0.020                     100.0                  4
  5         0.500       0.020                     100.0                  4
  6         0.500       0.020                     100.0                  4
  7         0.500       0.020                     100.0                  4

 Keplerian a priori orbital errors(ppm) + force paramt(percent)
 Sat#   Semiaxis    Eccen.  Inclin.  Asc.node  Perigee   M.anom.    rad1     rad2     rad3

  1      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  2      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  3      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  4      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  5      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  6      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  7      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 

   Session 1

 Stations used
    1   2   3   4   5   6   7  
    Y   Y   Y   Y   Y   Y   Y   

 Satellites used
    1   2   3   4   5   6   7  
    Y   Y   Y   Y   Y   Y   Y   

 Assumed ionosphere error
 constant :     0.0  ppm :    1.00
  
        Number of double difference observations: 
     satellite prn           3    6    8    9   11   12   13
 OBS   1 CCATOA.278        144  191   33  199  137   56  192
 OBS   2 CLOVEA.278        293  457   93  421  306  110  392
 OBS   3 CMOJAA.278        220   46   26   26   21   96  207
 OBS   4 CPVERA.278        301  508  112  445  318  111  397
 OBS   5 CSAFEA.278        211  301   48  321  234   55  332
 OBS   6 CWSFDA.278         61  350  126  259  263   35  164
 OBS   7 CYKNFA.278          0  223   68  181  139   35   88

 number of good oneway phases:   4245
 number of single differences:      0
 number of double differences:   2338

Inspection of the observation summary will reveal whether or not there were adequate data obtained from each of the satellites to determine its orbit.  Often there are not from a single session, particularly if it is less than 24 hours long or has only a continental-scale fidicial network.  In the example shown, no double differences could be formed with Yellowknife for PRN 3, so that its orbital parameters are poorly determined from the data.

The next part of the Q-file gives a summary of the solution controls, a list of the original X-files and the C-files created by the run, and the data statistics:

       USER  SOLN  DIFF  PHASE CONSTRAINTS BIASES       PARAMETERS      H-FILE
 KEYS: DEFLT QUICK DBLE  LC    NOION NOATM NONE  STN   ORB   NOZEN NOCLK  GCR  

 Ephemeris and survey data files          (q4znqa.278      1993/12/21  11:12:55)
 TVENT7.278       XCATO7.278       CCATOA.278      
                  XLOVE7.278       CLOVEA.278      
                  XMOJA7.278       CMOJAA.278      
                  XPVER7.278       CPVERA.278      
                  XSAFE7.278       CSAFEA.278      
                  XWSFD7.278       CWSFDA.278      
                  XYKNFD.278       CYKNFA.278      
 MERGE File: mvent1.278      

 Double-difference observations:   2338
 Epoch numbers    1 to  225  Interval:   120 s
 Start time:   87  10   5  14   37   55.080

 Total parameters:   133   live parameters:    91
 Prefit nrms:  0.34258E+01    Postfit nrms: 0.28306E+00
 -- Uncertainties not scaled by nrms

 Assumed standard deviation of measurement error:
   Constant term: 10.00 mm   Distance term:  0.00 ppm

 Channels used:      1     2     3     4     5     6     7    
                    569   568   311   754   765   340   938

 Correlation coefficients greater than 0.98:

  ORBIT ELEMENT 5 PN08  ORBIT ELEMENT 3 PN08 : -0.99136
  ORBIT ELEMENT 6 PN08  ORBIT ELEMENT 3 PN08 :  0.98318
  ORBIT ELEMENT 5 PN11  ORBIT ELEMENT 2 PN11 : -0.99167

The predicted postfit nrms for this solution was 0.288, indicating that the rms of the double-difference residuals is well below 1 cycle.  (If the data from each baseline were used independently, then you could use this nrms value, along with the data weighting [nominally 64 mm, or 0.3 cycles in LC] to compute the average rms of the residuals; e.g., ~ 0.288 x 0.3 = 0.09 cycles [18 mm] in this case.)

Next follows a listing of all the estimated parameters with their adjustments and uncertainties.  The station coordinates have the form

       Label (units)            a priori     Adjust (m)    Formal  Fract     Postfit
    1*CATO GEOC LAT (DMS)   N33:54:26.75445     0.0014     0.0192   0.1  N33:54:26.75450
    2*CATO LONG (DMS)      W118:47:08.75979    -0.0029     0.0500  -0.1 W118:47:08.75988
    3*CATO RADIUS (KM)      6372.2845106000     0.0173     0.0572   0.3    6372.28452789

The parameter adjustments and formal uncertainties are given in units of meters.  Fract  is the adjustment as a fraction of the formal error.  Scanning these values in the solution is useful to spot anomalous adjustments and also tells you whether you need to iterate in order to achieve adjustments unaffected by non-linearities in the partial derivatives.  The uncertainties are the formal errors of the least squares fit based on the assigned data weighting.   They have not been scaled by the a posteriori variance of unit weight (the nrms) since (temporal) correlations among phase observations usually renders this value unduly optimistic.  The uncertainties of the coordinates of station CATO (Castro) with respect to the nearest fixed station (Palos Verdes, 50 km away, in this example) are of order 5 cm, an acceptable value for a single-session quick solution with a relatively weak fiducial network (Palos Verdes – Yellowknife – Westford).  We should expect from this result that a multi-day solution with phase ambiguities resolved would produce uncertainties of 1 cm or less.  

Next are given the adjustments to the atmospheric zenith delays for each station, either a constant over the session or the tabular points of a piecewise linear function.  In this example, we are estimating 4 tabular points over the 7.5-hr session, so that the tabular points are 2.5 hr apart.  The adjustments in this case are less than 2 cm and less than the uncertainties of 3–4 cm.  The O-file includes with the zenith delay estimates the time of each tabular point so that they may be easily plotted.

   22*CATO ATMOS- 1 1          0.0000000000    -0.0135     0.0421  -0.3      -0.01348324
   23*CATO ATMOS- 2 1          0.0000000000    -0.0005     0.0369   0.0      -0.00049137
   24*CATO ATMOS- 3 1          0.0000000000     0.0139     0.0297   0.5       0.01391428
   25*CATO ATMOS- 4 1          0.0000000000    -0.0050     0.0321  -0.2      -0.00496773

In the main parameter list, as in the G-file, the orbital elements are given in terms of the Cartesian initial conditions in km and km/s.  The  adjustments and uncertainties, however, are given in m and m/s for ease of interpretation:

   71*ORBIT ELEMENT 1 PN03-13976.9094676840    12.3386    47.8665   0.3  -13976.89712908
   72*ORBIT ELEMENT 2 PN03 22548.1011499110    10.4451    12.8317   0.8   22548.11159502
   73*ORBIT ELEMENT 3 PN03  3693.2210527633    -5.4776    45.5426  -0.1    3693.21557517
   74*ORBIT ELEMENT 4 PN03    -1.1970220165     0.0005     0.0084   0.1      -1.19702148
   75*ORBIT ELEMENT 5 PN03    -1.3320686827     0.0031     0.0067   0.5      -1.33206561
   76*ORBIT ELEMENT 6 PN03     3.3985770848     0.0007     0.0023   0.3       3.39857778
   77 RAD PRES DIRECT PN03     1.0000000000     0.0000
   78 Y AXIS BIAS     PN03     0.0000000000     0.0000
   79 Z AXIS BIAS     PN03     0.0000000000     0.0000

In this example, the initial conditions in position for PRN 3 adjusted (from the broadcast orbit) by about 15 m.  The largest uncertainty is 48 m, about 2 ppm (of the orbital altitude), a factor of two larger than the uncertainty in the coordinates of station Castro with respect to Palos Verdes.  Since Cartesian initial conditions are difficult to interpret, particularly for multi-day arcs, a summary of orbital uncertainties in terms of Keplerian elements is given at the bottom of the Q-file:

  Post-fit Keplerian orbital errors in parts in 10**7

          a         e         I       Node   Perigee    M Anom.     w+M
 PRN  3   13.800     4.423    10.498    10.131   648.530   669.329    28.497  

This summary for PRN 3 shows that the semi-major axis, a, (representing the orbital period, in accordance with Kepler's third law) is determined with an uncertainty of 1.4 ppm, not unreasonable for the analysis of a single (~5 hr) pass, less than half an orbital period.  The orientation of the orbital plane, given by the inclination, I, and the longitude of the ascending node, is also determined to about 1 ppm.  The next two elements, the argument of perigee and mean anomaly are intrinsically poorly defined for a near-circular orbit; hence, the more meaningful measure of the along-track uncertainty is their sum, indicated here by w + M  (since w is the usual symbol for argument of perigee).  This component is almost always the least well determined, so the uncertainty in w + M will match closely the largest uncertainty in the Cartesian initial conditions.

Also summarized at the bottom of the Q-file are the values and uncertainties of baseline components, computed from the coordinate uncertainties and their correlations.  For example, the uncertainty of station Castro with respect to Palos Verdes is given as 

 Baseline vector (m ): Castro Peak (Site 1) to PVER7268    (Site 4)
 X    21204.6105 Y(E)   -34955.4573 Z   -31909.6755  L    51862.7698
      +-  0.0438         +-  0.0453      +-  0.0330       +-  0.0342  (meters)
 correlations (x-y,x-z,y-z) =    0.19676  -0.69426  -0.63151
 N   -37877.3127 E       35416.5889 U      -849.2942  L    51862.7698
      +-  0.0164         +-  0.0402      +-  0.0563       +-  0.0342  (Meters)
 Correlations (N-E,N-U,E-U) =   -0.40594  -0.09584  -0.16049

The baseline vectors are given both in a geocentric reference frame (XYZ) and in local coordinates (north, east, up) tangent to a sphere (not a reference ellipsoid) at the first station of each pair.  The sense of the vector is (second station – first station).  This presentation of uncertainties is particularly helpful in evaluating the baseline uncertainties for closely spaced stations, neither of which was held fixed in the solution, since in this case the estimates of their coordinates will be highly correlated. 

5.5  Evaluating the Final Solution

If you have selected LC as Choice of Observable for your final solution (i.e., you do not wish to attempt ambiguity resolution), then evaluation of the Q-file output is nearly the same as for the quick solution.  An nrms value of about 0.3 indicates that there are probably  no unflagged cycle slips in the data and no significant systematic model errors.  In a solution using 6–8 hours of 30-s data with an a priori  uncertainty of 10 mm, you should expect formal uncertainties of 5–10 mm in the north component, 10–20 mm in the east component, and 20–40 mm in the vertical component of most baselines.   

For most networks and observing scenarios, resolution of the phase ambiguities will improve your estimates of baseline coordinates, particularly the east component, and should be attempted.  It's a complicated process, however, and to be performed reliably requires that the analyst have both a thorough understanding of the sources of error in GPS observations and knowledge of the algorithms being applied in the software she or he is using.  Before reading the rest of this section, you should review the discussions of ambiguity resolution in Dong and Bock [1989] and Blewitt [1989] (see references in Chapter 2).

The procedure invoked by Choice of Observable = LC_HELP is a modification of the one discussed by Dong and Bock, the primary differences being the constraint of orbital and station parameters and the simultaneous use of pseudo-ranges in determining the wide-lane biases.  (The Dong and Bock procedure can be invoked by selecting Choice of Observable = L1&L2.)   This procedure has five steps: 
1)	Use the LC observable to estimate all parameters, including (real-valued) "biases" for each independent double difference combination.  This solution becomes the "biases-free" solution  recorded in the Q-file.
2)	Fix all geodetic parameters at the values estimated in step 1), and estimate only the "wide-lane" (L2-L1) biases, this time using the L1 and L2 observations separately with constraints on the ionosphere.  
3)	Using the decision function described by Dong and Bock, and pseudo-ranges if available at both frequencies, fix as many of the wide-lane biases as possible to integer values.
4)	With the wide-lane biases determined in step 3) held fixed, use the LC observations to estimate geodetic parameters and "narrow-lane" (L1) biases.  
5)	Using both a decision-function and "chi-square-search" criteria, fix as many of the narrow-lane biases as possible to integer values.  
6)	With the narrow-lane biases determined in step 5) held fixed, use the LC observations to estimate geodetic parameters.   This step produces the "biases-fixed" solution recorded in the Q-file. 

Each of these steps can be best understood by reference to the Q-file output.

As for the quick solution, the coordinates of Palos Verdes, Yellowknife, and Westford were given a priori constraints of 10 mm.  These constraints are again echoed in the Q-file but have not been shown here.  

          Program SOLVE Version 9.33 of 93/12/22 13:15:00 (apollo)

 SOLVE Run on 1993/12/27   9:11:36
 OPERATOR : rwk             

 Geocentric Coordinates Option

  LC solution with ionosphere constraint bias-fixing
  Assumed standard deviation of measurement error:
   Constant term:    10.0 mm   Distance term:  0.00 ppm

 Tracking stations:
  1..  Castro Peak 
  2..  Loma Verde P
  3..  MOJAVE GPS  
  4..  PVER7268    
  5..  San Fernando
  6..  WSFD GPS    
  7..  YELLOWKNIFE 

 Satellites observed:
  1..  PRN  3
  2..  PRN  6
  3..  PRN  8
  4..  PRN  9
  5..  PRN 11
  6..  PRN 12
  7..  PRN 13

    A priori coordinate errors in meters
Station    Latitude  Longitude  Radius

  1       100.000    100.000    100.000
  2       100.000    100.000    100.000
  3       100.000    100.000    100.000
  4         0.010      0.010      0.010
  5       100.000    100.000    100.000
  6         0.010      0.010      0.010
  7         0.010      0.010      0.010

   A priori zenith delay     Model = PWL
Station  ZEN_APR (m)   ZEN_VAR (m/sqrt(hr))  Correlation time (hrs)  # of delays

  1         0.500       0.005                     100.0.                 4
  2         0.500       0.005                     100.0                  4
  3         0.500       0.020                     100.0                  4
  4         0.500       0.020                     100.0                  4
  5         0.500       0.020                     100.0                  4
  6         0.500       0.020                     100.0                  4
  7         0.500       0.020                     100.0                  4

 Keplerian a priori orbital errors(ppm) + force paramt(percent)
 Sat#   Semiaxis    Eccen.  Inclin.  Asc.node  Perigee   M.anom.    rad1     rad2     rad3

  1      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  2      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  3      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  4      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  5      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  6      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 
  7      0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05   0.1E+05  0.1E+04  0.1E+04  0.1E+04 

   Session 1

 Stations used
    1   2   3   4   5   6   7  
    Y   Y   Y   Y   Y   Y   Y   

 Satellites used
    1   2   3   4   5   6   7  
    Y   Y   Y   Y   Y   Y   Y   

 Assumed ionosphere error
 constant :     0.0  ppm :    1.00
  
        Number of double difference observations: 
     satellite prn           3    6    8    9   11   12   13
 OBS   1 CCATOA.278        142  191   33  199  137   55  191
 OBS   2 CLOVEA.278        292  457   93  421  306  110  391
 OBS   3 CMOJAA.278        220   46   26   26   21   96  207
 OBS   4 CPVERA.278        300  508  112  445  318  110  397
 OBS   5 CSAFEA.278        211  301   48  321  234   55  332
 OBS   6 CWSFDA.278         61  350  126  259  263   35  164
 OBS   7 CYKNFA.278          0  223   68  181  139   35   88

 number of good oneway phases:   4241
 number of single differences:      0
 number of double differences:   2336

The summary of double difference observations is important because a small number for a given station or satellite may prevent resolution of ambiguities for combinations involving that station or satellite.

At the end of the observation summary, you may see the following:

 fix dependent bias param. of index  161
 
 fix dependent bias param. of index  196

This message means that the absence of data for certain station/satellite combinations forced SOLVE to "fix" (remove from the solution) one or more ambiguity parameters that it had defined prior to reading in the data.  The message is no cause for concern.

If precise P1 and P2 pseudoranges are not available, then the wide-lane ambiguity parameters are separated from ionospheric effects by constraining the differential ionosphere at each epoch.  The value of 1 ppm is appropriate for a relatively quiet ionosphere, as might be present in the daytime a mid-solar cycle, or at night near solar maximum (as was the case here).   Values of the ionospheric constraint as large as 8 ppm can be effective in resolving wide-lane ambiguities and are realistic for daytime observations near solar maximum.  Using the ionospheric contraints or precise pseudoranges, SOLVE estimates real-valued wide-lane ambiguity parameters ("biases").  These parameters are then "fixed" to integer values using the decision function and chi-square search algorithm and, if available, precise pseudoranges as described in Dong and Bock.  The parameters  (input or default) and specific algorithm used are echoed in the Q-file:

 Wide-lane bias-fixing criteria
 deviation :  0.15  sigma :  0.15  decision func. :   1000.0 ratio :   10.0

       ==== estimate and fix wide-lane (L2-L1) ambiguities =+==

  Algorithm: LC_HELP
  L2-L1 biases estimated from phases and ionospheric constraint using the decision
  function and chi-square search.  If a bias is not fixed using the decision function
  and P2 pseudo-range (PR) is available, the PR wide-lane estimate is used with the
  PR decision function if
       |PR estimate - phase estimate| < 0.4 cycle
  Finally, for biases fixed with the decision function, the PR estimates overrides if
       PR estimate is a factor of two closer to an integer than the phase estimate.  For codeless receivers, half-integer values are allowed.

  L1,L2 estimate of biases with  1.0 ppm ionosphere constraint
  all orbit, site and atmosphere parameters forced from LC

  Chi2= 0.32683E+05  Normalized rms= 0.26644E+01  parameters=  68

     --- bias uncertainties scaled by nrms !

The three decision-function parameters are the deviation from an integer (cutdev) and  standard deviation (cutsig) that define the rounding area described in  Dong and Bock (Figure 4 and Appendix A).   The third parameter (decision function) is the inverse of the probability for making a type 1 error (fixing the amibiguity at the wrong integer value).  The decision-function rounding algorithm is sensitive primarily to the value chosen for cutdev.  Decreasing or increasing it from the default value of 0.15 cycles has the effect of making your resolution of ambiguities more or less conservative.   Though the algorithm is less sensitive to cutsig, it makes sense to change it to match the value of cutdev when specifying these parameters in the sestbl.  The fourth parameter displayed (wlrat) is the cutoff ratio for the chi-square searching algorithm that is invoked after rounding.  The current coding of this algorithm ignores correlations among the ambiguity parameters; hence the value of the ratio that represents a significant increase in chi-square is very sensitive to the number of parameters in the solution (i.e., the size of the network).  The default value of 10. is moderately conservative for most networks.  

If a wide-lane ambiguity is not resolved with the decision function and precise pseudoranges are available, the pseudorange estimate is also used.  The criteria for fixing a real-valued estimate to an integer are that the uncertainty (sigma) of the estimate be less than 0.15 cycle, that the estimate be within 0.3 cycles or 3-sigma of an integer, whichever is smaller, and that the difference of the pseudorange and phase estimate be less than 0.8 cycles.  This last requirement is to guard against a spurious pseudorange estimate that might be fortuitously close to an integer.  The pseudorange estimate is allowed to override the decision-function estimate if the former has an uncertainty less than 0.1 cycles and is a factor of two closer to an integer .  A warning is printed if both the phase and pseudorange estimates are apparently good but close to different integers. 

If you want to give higher priority to the pseudorange estimate, you can specify a slightly different algorithm identified as LC_RANGE in the sestbl. input.  With this algorithm, the wide-lane bias is fixed from the pseudorange estimate if the deviation is within 0.4 cycle and not greater than 3-sigma.  If these criteria are satisfied, no check against the ionosphere-constrained estimate is made.  If not, then the decision function is invoked to attempt to resolve the ambiguity.    

The uncertainties obtained for the biases in the wide-lane solution are scaled by the nrms (unlike the uncertainties estimated in the complete solutions), so the ability of the decision function to fix the biases is reduced if the ionospheric constraint is too tight.  In the example shown, the nrms is 2.66, a reasonable value for moderate ionosopheric conditions.  (On the other hand, if the constraint is too loose, the wide-lane uncertainties will also go up because the estimator will be unable to separate the wide-lane and narrow-lane bias parameters.)  The uncertainties from the pseudo-range solution are not influenced by the level of ionospheric error and should be reliable if the pseudorange observations are sufficiently precise (when averaged over the session) and not corrupted by multipath.

Next follows a lengthy summary (truncated in this documentation) of the estimation of the biases from the ionosphere-constrained L1 and L2 observations.  In this solution, the station and orbital parameters have been fixed at their values from an LC, biases-free solution which SOLVE has performed but does not write to the Q-file until later.   First in the summary are the narrow-lane (L1) biases (designated B1L1), which should theoretically be integers but may not be close to integers in this solution due to ionospheric errors.  Following these are the wide-lane (L2–L1) biases (designated B1L2), which because of their larger wavelengths are more likely to be close to integers even in the presence of ionospheric errors.  (The B1 in the designation refers to "biases from session 1".)  For brevity, we show below only the values for the 32-km baseline between Castro Peak (CATO) and San Fernando (SAFE) and the 52-km baseline between Castro Peak and Palos Verdes (PVER).

        Label (units)            L1,L2 est.  Uncertainty        PR est.  Uncertainty

..140*B1L1 CATO-SAFE  6- 3           11.852     0.038      
  141*B1L1 CATO-SAFE  6- 8           65.828     0.050      
  142*B1L1 CATO-SAFE  6- 9           11.990     0.030      
  143*B1L1 CATO-SAFE  6-11           -5.219     0.030      
  144*B1L1 CATO-SAFE  6-12           11.915     0.045      
  145*B1L1 CATO-SAFE  6-13           -0.152     0.032      
  146*B1L1 CATO-PVER  6- 3          -25.029     0.038      
  147*B1L1 CATO-PVER  6- 8          -73.110     0.041      
  148*B1L1 CATO-PVER  6- 9          -25.054     0.028      
  149*B1L1 CATO-PVER  6-11            3.874     0.029      
  150*B1L1 CATO-PVER  6-12          -25.196     0.044      
  151*B1L1 CATO-PVER  6-13            0.000     0.031      
...
  175 B1L21CATO-SAFE  6- 3           -0.945     0.054            -1.240     0.188
  176 B1L21CATO-SAFE  6- 8          -15.018     0.070           -15.751     0.238
  177 B1L21CATO-SAFE  6- 9           -0.979     0.042            -1.316     0.174
  178 B1L21CATO-SAFE  6-11            1.994     0.043             1.698     0.182
  179 B1L21CATO-SAFE  6-12           -0.921     0.064            -1.243     0.202
  180 B1L21CATO-SAFE  6-13           -0.001     0.045            -0.428     0.174
  181 B1L21CATO-PVER  6- 3            5.047     0.053             5.125     0.179
  182 B1L21CATO-PVER  6- 8           16.052     0.058            15.862     0.218
  183 B1L21CATO-PVER  6- 9            5.007     0.040             4.950     0.168
  184 B1L21CATO-PVER  6-11           -0.955     0.040            -1.013     0.173
  185 B1L21CATO-PVER  6-12            6.005     0.062             6.203     0.203
  186 B1L21CATO-PVER  6-13            1.023     0.044             0.897     0.167
...
    Fix No.  180  bias  from     0.00   to     0.0
    Fix No.  178  bias  from     1.99   to     2.0
...
    Fix No.  183  bias  from     5.01   to     5.0
    Fix No.  185  bias  from     6.00   to     6.0
    Fix No.  186  bias  from     1.02   to     1.0
    Fix No.  177  bias  from    -0.97   to    -1.0
    Fix No.  176  bias  from   -15.02   to   -15.0
    Fix No.  181  bias  from     5.03   to     5.0
    Fix No.  175  bias  from    -0.97   to    -1.0
    Fix No.  184  bias  from    -0.95   to    -1.0
    Fix No.  182  bias  from    16.04   to    16.0
    Fix No.  179  bias  from    -0.93   to    -1.0

     --- bias uncertainties scaled by nrms !

In the example shown, SOLVE resolved all of the CATO–SAFE and CATO–PVER wide-lane ambiguities using the decision function with the ionosphere-constrained phase estimate.  With one exception (No. 176), the phase and pseudorange estimates are consistent.  The uncertainties in the pseudorange estimates would have been a factor of two smaller had we used 30-s rather than 120-s sampling.  For receivers that have no P-code range, the widelane ambiguities can assume half-wavelength values, making resolution more difficult.

Next in the Q-file is a summary of both the narrow-lane and wide-lane biases after the resolution of as many as possible of the wide-lanes.  The narrow-lane bias estimates are slightly changed, and have smaller uncertainties, but will be close to integers only if  ionospheric effects are small (as is in fact the case for this experiment).  The main purpose of this summary is to highlight the wide-lane biases that have been fixed at integers and those for regional baselines that remain unresolved.  Using this summary and the preceeding one, you should evaluate whether or not it may be possible to resolve the remaining (regional) wide-lane ambiguities by changing the ionospheric constraint or editing the data.   You can use CVIEW, for example, to inspect the residuals for the station–satellite combinations in question to see whether the departure from an integer is due to an excursion in only part of the pass—in the phase estimate due the ionosphere or in the pseudo-range estimate due to multipath—in which case you could unweight the offending data.  Note that the pseudorange estimate is made using the full one-way span of data for each station and satellite so that multipath corruption of the wide-lane combination may not be visible if you display only double differences in CVIEW.

     == summary of wide-lane biases after fixing ==

        Label (units)            L1,L2 est.  Uncertainty        PR est.  Uncertainty
...
  140*B1L1 CATO-SAFE  6- 3           11.880     0.027      
  141*B1L1 CATO-SAFE  6- 8           65.819     0.035      
  142*B1L1 CATO-SAFE  6- 9           12.000     0.021      
  143*B1L1 CATO-SAFE  6-11           -5.222     0.022      
  144*B1L1 CATO-SAFE  6-12           11.955     0.032      
  145*B1L1 CATO-SAFE  6-13           -0.153     0.023      
  146*B1L1 CATO-PVER  6- 3          -25.006     0.027      
  147*B1L1 CATO-PVER  6- 8          -73.085     0.030      
  148*B1L1 CATO-PVER  6- 9          -25.051     0.020      
  149*B1L1 CATO-PVER  6-11            3.896     0.020      
  150*B1L1 CATO-PVER  6-12          -25.193     0.032      
  151*B1L1 CATO-PVER  6-13            0.012     0.022      
...
  175 B1L21CATO-SAFE  6- 3           -1.0                        -1.240     0.188
  176 B1L21CATO-SAFE  6- 8          -15.0                       -15.751     0.238
  177 B1L21CATO-SAFE  6- 9           -1.0                        -1.316     0.174
  178 B1L21CATO-SAFE  6-11            2.0                         1.698     0.182
  179 B1L21CATO-SAFE  6-12           -1.0                        -1.243     0.202
  180 B1L21CATO-SAFE  6-13            0.0                        -0.428     0.174
  181 B1L21CATO-PVER  6- 3            5.0                         5.125     0.179
  182 B1L21CATO-PVER  6- 8           16.0                        15.862     0.218
  183 B1L21CATO-PVER  6- 9            5.0                         4.950     0.168
  184 B1L21CATO-PVER  6-11           -1.0                        -1.013     0.173
  185 B1L21CATO-PVER  6-12            6.0                         6.203     0.203
  186 B1L21CATO-PVER  6-13            1.0                         0.897     0.167

After determining as many as possible of the wide-lane ambiguities, SOLVE fixes these at integer values and performs an LC (ionsophere-free) solution for all of the geodetic parameters and the narrow-lane bias parameters.  This solution is identified by the keyword summary preceeding it:

       USER  SOLN  DIFF  PHASE CONSTRAINTS BIASES       PARAMETERS      H-FILE
 KEYS: DEFLT FULL  DBLE  LC    NOION ATM   FREE  STN   ORB   ZEN   NOCLK  GCR  

 Total parameters:   203   live parameters:   125
 Prefit nrms:  0.11146E+03    Postfit nrms: 0.28993E+00
 -- Uncertainties not scaled by nrms

 Assumed standard deviation of measurement error:
   Constant term: 10.00 mm   Distance term:  0.00 ppm

The listing of parameters and their adjustments and uncertainties is the same as for the quick solution and will not be repeated here except for the CATO-PVER-SAFE subset of the regional baselines and their corresponding L1 bias parameters:

       Label (units)            a priori     Adjust (m)    Formal  Fract     Postfit
...
  140*B1L1 CATO-SAFE  6- 3     0.0000000000    11.6581     0.5723            11.65807935
  141*B1L1 CATO-SAFE  6- 8     0.0000000000    65.8913     0.1882            65.89133136
  142*B1L1 CATO-SAFE  6- 9     0.0000000000    11.9175     0.1747            11.91745376
  143*B1L1 CATO-SAFE  6-11     0.0000000000    -5.1967     0.1809            -5.19674843
  144*B1L1 CATO-SAFE  6-12     0.0000000000    11.6353     0.4216            11.63530070
  145*B1L1 CATO-SAFE  6-13     0.0000000000    -0.1487     0.2789            -0.14873417
  146*B1L1 CATO-PVER  6- 3     0.0000000000   -25.1930     0.5377           -25.19297755
  147*B1L1 CATO-PVER  6- 8     0.0000000000   -73.2937     0.2363           -73.29373741
  148*B1L1 CATO-PVER  6- 9     0.0000000000   -25.0793     0.2417           -25.07928650
  149*B1L1 CATO-PVER  6-11     0.0000000000     3.7142     0.2678             3.71420827
  150*B1L1 CATO-PVER  6-12     0.0000000000   -25.2138     0.6219           -25.21380623
  151*B1L1 CATO-PVER  6-13     0.0000000000    -0.0814     0.3157            -0.08141277

 Baseline vector (m ): Castro Peak (Site 1) to PVER7268    (Site 4)
 X    21204.6177 Y(E)   -34955.4282 Z   -31909.6883  L    51862.7611
      +-  0.0315         +-  0.0349      +-  0.0274       +-  0.0210  (meters)
 correlations (x-y,x-z,y-z) =    0.43474  -0.80683  -0.82133
 N   -37877.3073 E       35416.5812 U      -849.3252  L    51862.7611
      +-  0.0076         +-  0.0253      +-  0.0476       +-  0.0210  (Meters)
 Correlations (N-E,N-U,E-U) =   -0.53586   0.02359  -0.21853

 Baseline vector (m ): Castro Peak (Site 1) to San Fernando (Site 5)
 X    22126.3911 Y(E)     5021.4860 Z    22600.1085  L    32024.3253
      +-  0.0302         +-  0.0383      +-  0.0256       +-  0.0122  (meters)
 correlations (x-y,x-z,y-z) =    0.30109  -0.74299  -0.75067
 N    27155.5494 E       16974.1256 U       112.2763  L    32024.3253
      +-  0.0103         +-  0.0273      +-  0.0468       +-  0.0122  (Meters)
 Correlations (N-E,N-U,E-U) =   -0.53520  -0.21402  -0.03318

From these estimates, SOLVE then attempts to resolve the narrow-lane ambiguities using first the decision-function criteria for rounding and then, if necessary, a comparison of chi-square values for sample choices of integers around the best estimate.  

. . .

 Narrow-lane bias-fixing criteria
 deviation :  0.15  sigma :  0.15  decision func. :   1000.0 ratio :   10.0
    Fix No.  137  bias  from    -9.02   to    -9.0
    Fix No.  136  bias  from    32.01   to    32.0
    Fix No.  135  bias  from   152.00   to   152.0
    Fix No.  139  bias  from    -0.08   to     0.0

In this case, none of the 12 narrow-lane ambiguities on the two selected baselines were resolved using the decision-function algorithm.  The primary reason for this poor performance is the relatively large uncertainties due to the weak fiducial network.  For the ambiguities not resolved by the decision function, SOLVE evaluates the chi-square ratio for a series of solutions generated with different values of the ambiguity parameters, tested five at a time beginning with those with the lowest uncertainties.

 LOWEST CHI-SQUARES:
         188.    216.    216.    216.    216.    222.    225.    232.    233.    236.

 (CHI2/CHI20 -  1.)*SQRT(NO. DEGS. OF FREEDOM):
         0.00    6.91    7.06    7.09    7.09    8.57    9.40   11.11   11.34   11.91

 PARAMETER    BIASES
  134    32.0    32.0    33.0    32.0    32.0    31.0    32.0    32.0    33.0    32.0
  138    32.0    32.0    32.0    31.0    33.0    32.0    32.0    32.0    33.0    33.0
  141    66.0    65.0    66.0    66.0    66.0    66.0    67.0    66.0    66.0    65.0
  142    12.0    12.0    12.0    12.0    12.0    12.0    12.0    11.0    12.0    12.0
  143    -5.0    -5.0    -5.0    -5.0    -5.0    -5.0    -5.0    -6.0    -5.0    -5.0

In this set of test solutions, only bias parameters 142 and 143 have the same value for all combinations producing a chi-square ratio less than the specified input value (10.0).  Thus, these bias parameters will be fixed to the integer values (12.0 and -5.0, respectively) and the remaining ones searched with new bias parameters (Nos. 145 and 151):

 LOWEST CHI-SQUARES:
         188.    202.    212.    217.    217.    218.    221.    223.    223.    224.

 (CHI2/CHI20 -  1.)*SQRT(NO. DEGS. OF FREEDOM):
         0.00    3.54    5.89    7.08    7.24    7.50    8.18    8.61    8.65    8.91

 PARAMETER    BIASES
  134    32.0    32.0    32.0    32.0    32.0    32.0    33.0    33.0    32.0    31.0
  138    32.0    32.0    32.0    31.0    32.0    33.0    32.0    32.0    32.0    32.0
  141    66.0    66.0    66.0    66.0    65.0    66.0    66.0    66.0    66.0    66.0
  145     0.0     0.0     0.0     0.0     0.0     0.0     0.0     0.0    -1.0     0.0
  151     0.0    -1.0     1.0     0.0     0.0     0.0     0.0    -1.0    -1.0     0.0

 Narrow-lane bias-fixing complete

In this search no bias has the same integer value for all test solutions producing a chi-square ratio less than 10., so the search algorithm terminates.

The last section of the Q-file gives the estimates of all of the geodetic parameters from an LC solution in which the resolved wide-lane and narrow-lane bias parameters are held fixed at integer values.  Again we list only the estimates for our two sample baselines:

       USER  SOLN  DIFF  PHASE CONSTRAINTS BIASES       PARAMETERS      H-FILE
 KEYS: DEFLT FULL  DBLE  LC    NOION ATM   FIXED STN   ORB   ZEN   NOCLK  GCX  

 Total parameters:   203   live parameters:   119
 Prefit nrms:  0.11131E+03    Postfit nrms: 0.29099E+00
 -- Uncertainties not scaled by nrms

 Assumed standard deviation of measurement error:
   Constant term: 10.00 mm   Distance term:  0.00 ppm

       Label (units)            a priori     Adjust (m)    Formal  Fract     Postfit
...
  140*B1L1 CATO-SAFE  6- 3     0.0000000000    11.7162     0.3818            11.71617683
  141*B1L1 CATO-SAFE  6- 8     0.0000000000    65.9206     0.1771            65.92061641
  142 B1L1 CATO-SAFE  6- 9     0.0000000000    12.0000
  143 B1L1 CATO-SAFE  6-11     0.0000000000    -5.0000
  144*B1L1 CATO-SAFE  6-12     0.0000000000    11.6779     0.2470            11.67791232
  145*B1L1 CATO-SAFE  6-13     0.0000000000    -0.0260     0.1783            -0.02595505
  146*B1L1 CATO-PVER  6- 3     0.0000000000   -25.1936     0.4600           -25.19357338
  147*B1L1 CATO-PVER  6- 8     0.0000000000   -73.2904     0.2033           -73.29036114
  148*B1L1 CATO-PVER  6- 9     0.0000000000   -25.1786     0.1938           -25.17861562
  149*B1L1 CATO-PVER  6-11     0.0000000000     3.7001     0.2096             3.70010747
  150*B1L1 CATO-PVER  6-12     0.0000000000   -25.2083     0.5967           -25.20825779
  151*B1L1 CATO-PVER  6-13     0.0000000000    -0.1467     0.2821            -0.14668282
...
  175 B1L21CATO-SAFE  6- 3     0.0000000000    -1.0000
  176 B1L21CATO-SAFE  6- 8     0.0000000000   -15.0000
  177 B1L21CATO-SAFE  6- 9     0.0000000000    -1.0000
  178 B1L21CATO-SAFE  6-11     0.0000000000     2.0000
  179 B1L21CATO-SAFE  6-12     0.0000000000    -1.0000
  180 B1L21CATO-SAFE  6-13     0.0000000000     0.0000
  181 B1L21CATO-PVER  6- 3     0.0000000000     5.0000
  182 B1L21CATO-PVER  6- 8     0.0000000000    16.0000
  183 B1L21CATO-PVER  6- 9     0.0000000000     5.0000
  184 B1L21CATO-PVER  6-11     0.0000000000    -1.0000
  185 B1L21CATO-PVER  6-12     0.0000000000     6.0000
  186 B1L21CATO-PVER  6-13     0.0000000000     1.0000

 Baseline vector (m ): Castro Peak (Site 1) to PVER7268    (Site 4)
 X    21204.6215 Y(E)   -34955.4322 Z   -31909.6894  L    51862.7659
      +-  0.0289         +-  0.0342      +-  0.0272       +-  0.0179  (meters)
 correlations (x-y,x-z,y-z) =    0.53672  -0.82989  -0.86191
 N   -37877.3090 E       35416.5864 U      -849.3245  L    51862.7659
      +-  0.0069         +-  0.0216      +-  0.0472       +-  0.0179  (Meters)
 Correlations (N-E,N-U,E-U) =   -0.49943   0.03739  -0.21814

 Baseline vector (m ): Castro Peak (Site 1) to San Fernando (L(Site 5)
 X    22126.3888 Y(E)     5021.4669 Z    22600.1089  L    32024.3210
      +-  0.0226         +-  0.0337      +-  0.0252       +-  0.0072  (meters)
 correlations (x-y,x-z,y-z) =    0.69596  -0.86032  -0.91844
 N    27155.5397 E       16974.1329 U       112.2914  L    32024.3210
      +-  0.0058         +-  0.0144      +-  0.0451       +-  0.0072  (Meters)
 Correlations (N-E,N-U,E-U) =   -0.39678  -0.09944  -0.07302

You'll note that the nrms is up slightly, from 0.2899 to 0.2910, as is expected with fewer parameters estimated, and that the uncertainty of the east component of the Castro–San Fernando baseline is reduced from 27 mm to 14 mm.  An important check on whether the phase ambiguities have been resolved correctly may be obtained by comparing the biases-free and biases-fixed estimates of the baseline vectors.  In this example the biases-free and biases-fixed estimates from the two solutions agree for all components within the (larger) biases-free uncertainties.

After SOLVE has completed the biases-fixed solution, it repeats both the biases-free and biases-fixed solutions with very loose constraints on all of the parameters in order to obtain an unbiased set of adjustments and covariance matrix for input to GLOBK.  These two solutions are saved in the H-file.  The details of the loosely constrained solution are written to the screen or log file but not saved in the Q-file.  The Q-file does record, however, the station, zenith-delay, and orbital constraints used and the normalized rms for the biases-free and biases-fixed solutions:

  Loose constraints.  All solutions and covariance matrix are stored in H-file.

 A priori coordinate errors in kilometers
 Latitude  Longitude  Radius
  1   0.10000   0.10000   0.10000
  2   0.10000   0.10000   0.10000
  3   0.10000   0.10000   0.10000
  4   0.10000   0.10000   0.10000
  5   0.10000   0.10000   0.10000
  6   0.10000   0.10000   0.10000
  7   0.10000   0.10000   0.10000

 Keplerian a priori orbital errors (dimensionless except semi-major axis (km))
 Semiaxis    Eccen.   Inclin.   Asc.node  Perigee   M.anom.  rad1   rad2   rad3
  1 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  2 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  3 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  4 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  5 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  6 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00
  7 0.260   1.0E-05   1.0E-05   1.0E-05   1.0E-05   1.0E-05 100.00 100.00 100.00

 A priori zenith-delay errors in meters
  1   1.0
  2   1.0
  3   1.0
  4   1.0
  5   1.0
  6   1.0
  7   1.0

 Total parameters:   203   live parameters:   124
 Prefit nrms:  0.11143E+03    Postfit nrms: 0.28617E+00
 -- Uncertainties not scaled by nrms

 Total parameters:   203   live parameters:   119
 Prefit nrms:  0.11131E+03    Postfit nrms: 0.28652E+00
 -- Uncertainties not scaled by nrms
Normal stop in SOLVE

5.6  Multi-session Solutions

The capability to perform multi-session solutions in GAMIT was developed to enhance ambiguity resolution by combining the information from multiple days or networks at a time when continental- or global-scale tracking networks were capable of determining orbits at the level of 50–100 ppb (see, e.g., Dong and Bock [1989]).  The multi-session feature is seldom used today and may not work properly with recent program enhancements.  Resolution of ambiguities for a regional network can almost always be accomplished today using a single session in conjunction with tight constraints on orbits obtained from global tracking.  Once ambiguities are resolved, GAMIT will loosen the constraints and create an H-file that can be combined in GLOBK with H-files from a global solution and from regional solutions for other sessions (days).  This process might involve some iteration:  resolution of ambiguities in GAMIT can be enhanced by putting tight (but realistic) constraints on the station coordinates and orbital parameters from a previous GLOBK solution which was performed using the "biases-free" output of GAMIT.

If a multi-session GAMIT run is necessary, some thought should be given to file naming and the organization of of the data.  The current restriction of X- and C-files to 9 characters limits the analyst's ability to differentiate between sessions within the same day.  This problem can be avoided in preparation and cleaning of the data by using separate directories for each session.  When finally combining the clean data in a multi-session solution, you can then rename the X- (or C-files) so that the 6th character is different ("a" for "am" and "p" for "pm" is one such scheme).  It is also usually convenient to run the multi-session solutions in a new directory, with links made to the input X- (or C-) files in the original session directories.