6.  Data Editing

6.1  Introduction   

Continuously tracked, doubly differenced carrier phase observations provide an extraordinarily precise data set for estimating GPS orbital parameters and relative site positions; but the strength of the data can be realized only if it is edited properly to be free of cycle slips over each tracking session.  Sometimes this is impossible, and we are forced to introduce additional "bias" (offset) parameters that effectively break the phase data into shorter and thus weaker segments.  The goal of the analyst (and/or the analysis software) is to remove cycle slips while introducing as few additional parameters as possible.  Too many additional bias parameters weakens the solution, but residual cycle slips not "covered" by bias parameters produce erroneous estimates of the important geodetic parameters.  To put the problem in perspective, recall that the most common slip in the ionosphere-free linear combination (LC), corresponding to one-cycle slips in L1 and L2, is 0.52 cycles, or 10 cm in equivalent pathlength.  Since our usual goal is few-millimeter estimates of station positions, a single undetected slip can be (but not always are) quite serious.

Strictly speaking, we require only that all cycle slips be fixed (or covered by bias parameters) in the doubly differenced phases since those are the data used by SOLVE in its estimation.  As a practical matter, however, the editing process is much simpler if cycle slips can be identified and repaired in the data from a single station–either in the one-ways or between-satellites-differences.  With "selective availability" (SA) now "on" for most of the Block II satellites, however, the one-way phase residuals are dominated by satellite-oscillator fluctuations that can vary by several cycles over a few minutes.  With the availability of precise dual-frequency pseudo-range, it is possible to identify and repair most cycle slips using the one-way "wide-lane" observable ( see the paper by Blewitt  [1990] referenced in Chapter 2).   For equal slips in L1 and L2, however, the wide-lane will not show a break.  In this case, editing algorithms must rely use doubly differenced phase observations, aided at times by the assumption of a quiet ionosphere and stable receiver clocks.  

With the large number of satellites and stations now used in most surveys, automatic editing is essential for the sanity of the analyst.  Fortunately, AUTCLN, the automatic editor developed by Tom Herring, has reached a level of maturity that it can handle both regional and global networks with only occasional manual intervention.  The key to efficient processing is learning to use the outputs of SOLVE, AUTCLN, and the GAMIT scanning routines to determine quickly if a problem exists, and then to use the interactive editor, CVIEW, together with AUTCLN to perform an effective fix.  In the next three sections we describe the most important features of these programs and how to run them.  Then in Section 6.5, we discuss efficient strategies for editing  

6.2  Automatic editing using AUTCLN, SINCLN, or DBLCLN

Two sequences of automatic editing programs are available.  The GAMIT /clean directory includes SINCLN and DBLCLN, which operate respectively on one-way and doubly differenced residuals.  These programs have been abandoned by most GAMIT users in favor of AUTCLN, which resides in the GLOBK suite of programs (directory /kf) and operates simultaneously on one-way and doubly differenced residuals.  AUTCLN is significantly more effective than SINCLN/DBLCLN in reducing the amount of manual editing required, in part because of more sophisticated algorithms and in part because it allows more control by the analyst.  If you do not choose to compile the /kf directory in its entirety, you may obtain AUTCLN executables for Sun and HP workstations and include these in your GAMIT /bin directory.

If SINCLN or DBLCLN is invoked as Clean Option with Data Status = RAW and a 0-, 1- or 2-ITERATION type of analysis, SINCLN is run using prefit residuals after the initial MODEL runs.  SINCLN is invoked one station at a time with the input and output C-files as command-line arguments (if the second is omitted, SINCLN uses the same name for input and output).  If P-code pseudo-range is available, SINCLN uses the "turbo-edit" algorithm described by Blewitt  to operate on "wide-lane" observations; if not, or if the wide-lane is unacceptably noisy, other editing schemes are applied to insure continuity of the four phase combinations, L1, L2, LC, and LG (see Chapter 2 and Section 6.3 below). The success of SINCLN in repairing cycle slips in the absence of precise pseudo-range depends strongly on the quality of the receiver and satellite clocks, the latter depending mainly on whether SA is on.  With a reasonably good receiver oscillator (10-9) and in the absence of SA, SINCLN is capable of repairing or correctly flagging over 90% of the possible cycle slips.  When SA is on, however, SINCLN cannot detect slips less than about 100 cycles although it will flag as a possible slip any gap in the data.  In this case, SINCLN should be viewed as a pre-filter for automatic editing of doubly difference residuals using DBLCLN or for interactive manual editing with CVIEW.

If DBLCLN is specified as Clean Option, SINCLN is first run using prefit residuals and then DLBLCN is run using the predicted postfit residuals from the SOLVE 'quick' solution.  DBLCLN may be invoked with the command-line argument of the M-file name, but it usually run from a batch file created by FIXDRV, with the form

mcalf1.002
002
y          Use post-fit residuals?
y          Use all these stations?
y          Use this series of C-files?
1          Increment C-file name, do not delete

where the first line gives the name of the M-file containing the C-file names and (if post-fit) the adjusted parameter values, the second line gives the day number (necessary if the M-file is for a multi-day solution), and the remaining lines establish the program controls as indicated by the comments.  The retention of the input C-file (line 6) allows you to check both the input and output of DBLCLN, which is sometimes not robust for large networks or very "dirty" data.  If you are confident of DBLCLN's abilities or squeezed for disk space, you may have the input files deleted by changing the last input parameter from "1" to "2".

If AUTCLN is specified as Clean Option, AUTCLN is executed after each set of MODEL runs.  (AUTCLN, unlike DBLCLN, does not read an M-file so cannot predict postfit residuals; thus, the second pass through MODEL with updated coordinates and orbital parameters is necessary to flatten the residuals.)  If the model is sufficiently good (the residuals sufficiently flat), AUTCLN can achieve almost the same level of success as an analyst using CVIEW (and sometimes better!).   Since AUTCLN uses a restricted rather than exhaustive search to determine the station and satellite for which a slip occurred, it runs much faster than DLBCLN for large networks.  AUTCLN is invoked with four command-line arguments:

	autcln [command-file]  [out C-file series ]  [D-file]  [input C-file series] 
			 	                   or	     [list of C-files]

The first argument gives the AUTCLN command-file name.  The command file can be omitted by substituting  ' ' for the file name, and AUTCLN will use the default values for all parameters.  The second argument is a single character used to determine the name(s) of the output C-files.   If an alphameric character is given (e.g. a), then the output C-file names will be the same as the input but with this character substituted for the 6th character of the input series (usually the last digit of the year or a letter).  Two special characters are used:  . to keep the same 6th character as the input files, overwritting the input files;  + to create new files with the 6th character incremented (i.e., [yr] => a, a => b).  If no character is given (i.e., ' ' used), then no updated C-files will be written.  The input C-files are specified either by a D-file name followed by a character indicating the series (6th character of name), or by a complete list of the C-files to be used.  FIXDRV creates one of two forms of the AUTCLN command-line:

	autcln autcln.cmd . dvent7.278 7

if the input C-files are to be deleted (overwritten and then incremented using the mvcf script), or

	autcln autcln.cmd + dvent7.278 7

if the old C-files are to be retained.

The following is a sample autcln.cmd file, listing the options most often invoked:

  remove_bias_cond 10.0 3.0 1800.0
  allow_one_bg yes
  min_elev 10
#  use_gamit_elev yes 
  use_cview_edit yes
  remove_first_bia yes 
  dd_return_size 100 25 5 
* Site dependent ion parameters
  ion_jump  fair  120  6 2 5
  ion_jump  kour  120  6 2 5
  ion_jump  yell  120  6 2 5
  ion_jump  darw  120  6 2 5
  ion_jump  mcmu  120  6 2 5
  ion_jump  trom  120  6 2 5
edit_site_sv algo 23 345 368
edit_site_sv trom 15 451 600

The command remove_bias_cond sets the criteria for removing a bias flag (setting an extra ambiguity parameter) at a possible cycle slip.  In determining the size of a cycle slip and deciding whether to retain a bias parameter, AUTCLN compares the chi-square values of the residuals for the series (station-satellite double pairs) calculated with the best and second-best integer values.  In general terms, the bias will be removed if the ratio of the second-best to the best is sufficiently high.  The first two arguments represent the critical ratio and minimum value used in the formula, explained in detail in Chapter 7.   The defaults are 12.0 and 3.0; the values shown (10. and 3.0) apply a slightly less conservative criterion.  The third argument is the maximum gap (in seconds) over which AUTCLN will consider removing the bias flag.  The default is 3600. (1 hour), which some analysts might consider far too risky.

The second command allow_one_bg deals with the case where all channels of a receiver slip at nearly the same time, preventing AUTCLN from patching unambiguously in the one-way observations.  By specifying yes to this command, you allow AUTCLN to select one channel (satellite) as 'base', patch it roughly in one-ways, and then patch all other channels with respect to it.  Since this option applies only to multiple-satellite slips, not multiple-station slips, allowing the patch will not create problems if the data are later combined in a different network configuration.  The default for this command is no, but yes will usually provide better editing.  Occasionally, however, AUTCLN will make a mistake in using this mode ( yes ) when the slips are at slightly different epochs. 

There are three ways you can control the minimum elevation for data to be examined and output by AUTCLN.  The general and flexible approach is provided by the use of the autcln.cmd entry min_elev in conjunction with the new sestbl. entry Elevation Cutoff for SOLVE.  With these two commands you can elect to clean the data to a low elevation cutoff and then run tests easily in SOLVE for different cutoff values.  The AUTCLN entry will override the low-elevation flag on the C-file input in the sittbl. and set by MODEL.   The AUTCLN cutoff cannot be set arbitrarily low because all receivers cannot be trusted to flag correctly corrupt data at the beginning of a pass.  A value of 10 (degrees) is reasonably safe if you're not sure of the characteristics of your receiver.  Control of the elevation-angle and signal-to-noise cutoff on a station-by-station basis can be done using the site_param entry described in Section 7.6.  Finally, setting use_gamit_elev = yes will cause AUTCLN to clean and output data to the elevation cutoff set in the C-file header by MODEL.  If use_gamit_elev is set to yes, the min_elev and site_param entries will be ignored.

The entry use_cview_edit controls whether the unweighting of data on the input C-files are to be accepted by AUTCLN.  The default value is no, giving AUTCLN freedom to reweight data previously unweighted by the analyst using CVIEW.

The command remove_first_bia controls whether an extra bias flag is left at the beginning of each one-way sequence.  AUTCLN inserts a flag automatically as part of its bookkeeping, and the default (no) is to leave them in.  Specifying yes to the command will instruct AUTCLN to remove these before writing out the C-files.  There should be no effect on the solution either way.  Leaving them in will force extra implicit-bias solutions when SOLVE runs and leave extraneous flags on the screen in CVIEW; taking them out risks overlooking the need for a legitimate initial double-difference bias when a satellite has set and risen during the session. 

The command dd_return_size specifies the number of data points to be used for cycle-slip repair in the widelane (WL), LC, and LG residuals, respectively.  The values shown are the defaults and are reasonable for sampling intervals of 120 seconds or less.  With sparser sampling, you may want to decrease the numbers.  With a quiet ionosphere, you will obtain better results by increasing the number of LG points to 10.  

The ion_jump  commands are used to loosen the point-to-point fluctuation allowed in the LG observable for near-polar or near-equatorial stations experiencing a high level of ionospheric fluctuation.  The first number specifies the maximum gap (in seconds) over which the test will be applied.  The maximum jump allowed will lie between the last two numbers (2 and 5 here, in cycles) depending on the value of the second number (a multiplier) and the fluctuation encountered in the (one-way) LG residuals for the station.  The actual algorithm is given in Chapter 7.  The default values are 240 (4 minutes) for the gap, 4.0 for the multiplier, and 0.8 and 5.0 for the minimum and maxium, respectively.  The more conservative values shown (120. 6. 2. 5.) are appropriate for polar and equatorial regions and with well behaved data can be used for all stations.  

Finally, the last set of commands are used to unweight selected data within the session.  The arguments are the 4-character station id, the PRN number, and the range of epochs to be unweighted.  These are data, identified by SCANDD and/or CVIEW, that cannot be correctly repaired using AUTCLN's algorithms.  They arise typically from misbehavior of the receiver and have small but important deviations from acceptable limits.  The preferred strategy for editing is to not make any corrections directly in CVIEW, but rather to effect a successful fix using the edit_site_sv command of AUTCLN.  The autcln.cmd file then becomes a record of all of the editing performed for the session.  As discussed in Section 6.4 you can create edit_site_sv lines for autcln.cmd automatically in your CVIEW session. 

AUTCLN produces two output files which are quite useful for diagnosing problems.  Usually you will need to examine only the summary file, autcln.sum.  The first two tables provide a compact indication of whether one or more stations or satellites are anomalous. The first is a summary of the clock behavior :

 Clock and Range noise statistics at iteration  3
 Site/PRN    Allan SD@100  #     Range rms    #
             sec  (ppb)            (mm)
 BRLD       19.761493   2832          596.9  16210 TRM
 KAIN       19.931665   2879          675.1  15939 TRM
 KIT3         .527232   2879          729.9  16307 TRB
 KUM6       10.105467    719         2061.0   3462 TRM
 . . . 
 PRN_01       .384611   1188
 PRN_02       .411166   1039
 PRN_05       .422517    984

The Allen standard deviation at 100s is given (in parts per billion) for each station and satellite.  Station clock values in excess of 50 ppb (5 parts in 108) indicate variations larger than those expected for well-tuned crystal oscillators in any of the commonly used receivers.  Atomic oscillators (Rubidium, Cesium, or Hydrogen-maser) should show values below 1 ppb.  A bad clock does not necessarily mean bad phase data but increases the chances of cycle slips and degrades the ability of AUTCLN to perform a proper edit.  The fourth column gives the rms of range noise in millimeters for each station.   For P-code receivers under non-AS conditions, these values should be under a meter; under AS, some will increase to 1000–2000 mm.  Values larger than this usually mean lots of bad range data or bad prefit residuals (station coordinate errors > 10 m).  

Following the clock summary is a listing of the number of bias flags added during the initial double-difference scan:

 DDScan bias flags added report for pass  1
 SITE PN01  02  05  06  07  09  14  15  16  22  23  24  25  26  27  28  29  31
 BRLD    6   2  10   8  14  18   6   4  10   6   4  12   7   0   2   2   0   0
 KAIN    0   0   0   0   0   0   0   0   1   1   0   0   0   0   0   1   0   0
 KIT3    0   0   0   0   0   0   0   0   0   0   0   0   0   2   0   0   0   0
 KUM6    0   2   0   0   2   4   0   0   0   0   0   2   0   0   0   0   0   0
 KUMB    0   0   0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0
 LHAS    0   0   0   0   0   0   0   0   0   0   0   0   0   1   0   0   0   1
In this example station BRLD is performing poorly relative to the others but may not have fatal errors.  Many bias flags added can mean either bad prefit residuals or bad phase data.  Too many flags for a satellite at more than one station usually represents the effect of an umodeled acceleration of the satellite (e.g., umodeled thrusting).  

The compact nature of the first two tables is convenient for spotting problems, but the actual condition of the data after editing is better reflected in the third table, which shows for each station and satellite the number of good data in the one-way sequence (Good), the number of data deleted in gaps between closely spaced bias flags (Gap), and the number of remaining bias flags that might be resolved (BF) (i.e., the number of separated by less than twice the maximum size over which a flag would be removed):

 SITE  PRN Good  Gap  BF  PRN Good  Gap  BF  PRN Good  Gap  BF  PRN Good  Gap  BF
 FORT PN01  657    0   0 PN02  699    4   0 PN04  649    0   0 PN05  681    0   0
      PN06  945    0   0 PN07  133    7   0 PN09  648    0   0 PN14  477    0   1
      PN15  444    0   1 PN16 1119    2   2 PN17  813    0   0 PN18  782    0   0
      PN19 1047    0   0 PN20  470    6   2 PN21  962    0   0 PN22 1125    0   0
      PN23  659    0   0 PN24  573    0   1 PN25    0    0   0 PN26 1132    0   0
      PN27 1058    0   1 PN28  640    0   0 PN29 1032    0   0 PN31 1128    0   0

 A number greater than a few dozen in the Gap column and/or greater than 3 in the BF column usually means bad prefit residuals or noisy data.  

The other tables in the autcln.sum file and the use of the autcln.out file for tracing problems are discussed in Chapter 7.

If you have the setenv variable of your .login file referencing the stdrel/help directory, you can take advantage of an extensive on-line help file for AUTCLN.  To view the current parameter defaults, type autcln defaults.  

6.3  Scanning the residuals to identify slips

There are several programs and scripts available to identify problematic data and to aid in the repair of cycle slips.  All take as input the M-file from a quick or full solution and operate on the predicted postfit LC doubly differenced residuals.  The most commonly used program, part of the batch sequence, is SCANDD.  You can run it directly by typing the program name and the M-file from the SOLVE solution: 

                                        scandd mventa.278

Omitting the M-file will put SCANDD into an interactive mode, allowing you to select only certain stations, scan pre-fit (rather than post-fit) residuals, or scan a set of C-files with different 6th character. 

SCANDD calculates the LC root-mean square (rms) of each double-difference series and searches for jumps in the doubly differenced LC residuals.  It also identifies all possible cycle slips and compiles a list of corrections that can be used directly as input to CVIEW.  SCANDD produces three output files, each with a slightly different summary of the doubly differenced residuals.  The file most analysts find easiest to use in identifying potential cycle slips is called vscan.out, which lists the largest LC "jumps" for each double-difference series.  A distinction is made between jumps that are associated with bias flags ("flagged"), which do not corrupt a "full" or "regular" SOLVE solution, and those that have not had extra bias flags assigned ("unflagged").  You can obtain a sorted version of this file by running the  shell script sortv to sort the file vscan.out by epoch and produce two additional files, one listing the largest slip for every double difference combination, the other (more useful for large networks) listing only the 80 worst slips.  Shown below is the output of the second of these files, named vxxxx1.ddd.worst, where the experiment name (xxxx), type of solution (1), and day number (ddd) are taken from the M-file name. 

80  worst jumps
 CHAN1 CHAN2 SIT1  SIT2   NDATA   RMS    EPOCH(F)  FLAGGED  EPOCH(U) UNFLAGD
   2     4     6     7     496    0.27     712     -1.02     713     -1.41
   2     4     7     9     441    0.45     712     +1.23     713     +1.40
   2     4     3     7     517    0.26     712     -1.21     713     -1.40
   2     4     7     8     529    0.40     712     +1.05     713     +1.38
   2     4     7    10     531    0.40     712     +1.38     713     +1.37
   2     4     1     7      21    1.16     712     -0.99     713     -1.34
   2     4     2     7     530    0.40     712     -1.07     713     -1.32
   2     4     4     7     532    0.40     712     -1.14     713     -1.30
   2     4     5     7     517    0.31     712     -1.13     713     -1.27
   1     3     7     9     165    0.20     423     -1.29     360     -0.40
   ... 68 lines deleted ...
   3     4     7    10     392    0.12     503     -0.19     366     -0.27

Created vshim1.350.sort
Created vshim1.350.worst
Print with: enscript -fCourier7 vshim1.350.sort
Print with: enscript -fCourier7 vshim1.350.worst

This file can be used as a guide to interactive editing using CVIEW since the epoch of the largest jump, and the double-difference combination affected, are shown.  In the list shown above, for example, the repeated appearance of the same computed unflagged ( U ) LC jump  at epoch 713 indicates that a cycle slip occurred at site 7 in either channel 2 or 4.  If renamed to cview.list, it can also be read into CVIEW and used to skip directly to the potential cycle slips in the list. 

A second summary of potential slips is file scan.dd.  It differs from vscan.out in listing all of the potential slips (not just the largest in each series) and suggesting the number of L1 and L2 cycles to be added or subtracted to fix them.  It also includes an indicator for bias flags on each of the channels.  By including all flagged and unflagged slips, however, scan.dd provides a larger and more complicated file than one usually needs after running AUTCLN.  To use scan.dd it is usually best to sort it by epoch by running program SORTER, which will ask you to select for inclusion slips assoicated with series with rms values above a given value:

% sorter

CHOOSE A LOWER BOUND TO SORT SCAN.RMS (e.g. 0.8) : 0.1

An rms below 0.1 cycle usually indicates that there are no slips in the series.  You may also exclude from the sorted list a satellite and/or station:

ENTER SAT AND SITE TO EXCLUDE (e.g. 3 0  or CR to skip) :

An abbreviated example of the output file, dd.srt, is shown below.  The column headers are not printed by the program but have been added here for clarity.

								       Predicted slip
           Epoch         LC full rms     Chan 1 Chan 2   Site 1  Site 2           L1                L2
   1  199       0.05       4    2    8    1      1.00      0.00
   2  199       0.05       4    2    9    1      1.00      0.00
   3  199       0.06       4    2    5    1      1.00      0.00
   4  199       0.06       4    2    6    1      1.00      0.00
   5  199       0.06       4    2   10    1      1.00      0.00
   6  199       0.07       4    2    3    1      1.00      0.00
...
 127  476       0.13       6    5   14    6      0.00     -1.00
 128  477       0.12       6    5   14    5      1.00      1.00
 129  477       0.13       6    5   14    9     -1.00     -2.00
 130  477       0.15       6    5   14    4     -1.00     -2.00

In this example, the repeated appearance of the same computed L1 jump at epoch 199 indicates that a cycle slip occured at site 1 in either channel 1 or 2.  The combinations shown for epochs 476 and 477 paint a less clear picture, but probably indicate multiple slips—at both epochs and/or more than one satellite or station.  

The third output of SCANDD is file scan.rms, which gives for each series the rms value calculated three different ways:  1) "full" (as in vscan.out and scan.dd), in which implicit biases are inserted when explicitly flagged by AUTCLN or CVIEW;  2) "quick" in which an implicit bias is inserted at all gaps; and 3) "total", in which no implicit biases are removed—i.e, the rms value will include all jumps in the phase.  This file is most helpful in identifying stations with receiver problems or satellites experiencing unmodeled translations (from, e.g., non-gravitational forces) or rotations (mis-modeled yaw during eclipse or "noon turn").   Like the scan.dd file, scan.rms file is sorted by program SORTER, producing three output files:

	rms.qui - LC-RMS for quick solution (any gap/flag starts a new rms) 
	rms.ful - LC-RMS for full  solution (any flag starts a new rms) 
	rms.tot - LC-RMS of the entire series (as in CVIEW). 

An abbreviated example of the file rms.ful is shown below, where the rms information (for "quick", "full", and "total") has been sorted in order of decreasing size of the "full" rms:
          
                Quick            Full        Total            No obs.      Chan 1    Chan 2    Site 1    Site 2
   1    0.18     0.18    0.18       21       5     1     2     1
   2    0.10     0.17    0.17       27       7     6     7     6
   3    0.16     0.16    0.16       12       6     4     3     1
....
  66    0.10     0.11    0.40       52       7     2     2     1
  67    0.10     0.11    0.11       39       4     1     5     1
  68    0.10     0.11    0.11       34       6     4     7     6

In this example, the smaller quick than full rms for series 2 indicates that there is an unflagged gap that may still have a slip.  The large (0.40 cycle) total rms for series 66 indicates that there is a flagged jump (probably at a gap) which could not be patched by AUTCLN.  With a largest full rms of 0.18 cycles, this solution is probably free of slips or unmodeled effects.  

A way of determining better whether cycle slips or bad modeling are causing the high rms  values for certain series is to run SHOWRMS.  The input is one of the sorted rms lists (from SORTER), and the output is a normalized distribution of the contribution of each station/satellite pair to the overall rms of the predicted postfit residuals:

 % showrms

Enter 1 for rms.qui 2 for rms.ful 3 for rms.tot
2
RMS DISTRIBUTION  (total rms = 1000)  example: 234 = 23.4%

stn|sum|--------------------------------------------------------------
 1: 227:  33  44   3  47  47  14  36
 2: 132:  22  25   7  18  22  11  25
 3: 139:  29  14  14  11   0  36  33
 4: 125:  22  22   7  18  25  11  18
 5:  80:  18  11   0  11  14   7  18
 6:  88:   0  18   7  14  22  11  14
 7: 205:   0  55  18  33  36  11  51
----------------------------------------------------------------------
sum -->  125 191  58 154 169 102 198
chn -->    1   2   3   4   5   6   7
Enter channel and/or station to be removed and see next distribution
      m, n  remove channel n at station m
      m, 0  remove all channel at station m
      0, n  remove channel n at all station
      0, 0  to quit

In this example, four of the highest contributions are from station 1 (channels 1,2,4, and 5), so we may want to see what happens to the distribution if we remove station 1 from the computation: 

1,0
RMS DISTRIBUTION  (total rms = 1000)  example: 234 = 23.4%
stn|sum|--------------------------------------------------------------
 1:   0:   0   0   0   0   0   0   0
 2:  88:  11  18   7  11  11  11  18
 3: 102:  22  14  14   3   0  25  22
 4:  88:  14  18   7   7  14   7  18
 5:  44:  11   0   0   3   7   7  14
 6:  58:   0  11   7   7  11  11  11
 7: 161:   0  40  14  25  29  11  40
----------------------------------------------------------------------
sum -->   58 102  51  58  73  73 125
chn -->    1   2   3   4   5   6   7
Enter channel and/or station to be removed and see next distribution
      m, n  remove channel n at station m
      m, 0  remove all channel at station m
      0, n  remove channel n at all station
      0, 0  to quit
0,0

Now channels 2 and 7 from station 7 stand out as the largest contributors to the overall rms.  The results of SHOWRMS should not by themselves lead you to remove a satellite or station from the solution since a higher rms value for a particular satellite or station may just indicate a longer span of observations.  The summary can, however, be used effectively as a guide for inspecting the residuals using CVIEW. 

6.4  Interactive editing using CVIEW

Program module CVIEW is the primary interactive tool of the analysis software.  It allows the analyst to display to the screen almost every imaginable combination of phase and pseudo-range residuals, as well as clock behavior and the sky tracks of the satellites.  For editing, it has a number of features which allow rapid and effective repairing of cycle slips, insertion and removal of additional bias parameters, and the unweighting of questionable data.  When an editing session is complete, CVIEW writes out a new set of C-files incorporating all of the analyst's changes.  CVIEW also accepts as input RINEX or X-files, allowing inspection of raw data when you suspect a receiver problem or want an early look at the ionosphere (LG) or widelane (WL) observables, neither of which depend on modeling the geometry.

To run the program type "CVIEW" with the name of an M-file, or omit the M-file argument and respond to the program's prompt for the name of an M- or C-file.  If you omit the M-file from the command line argument, the program will display the names of all the C-files used, giving you the opportunity to select a subset of the files and/or to change the sixth character of the C-file names listed so as to read in a different set.  The program will also ask if you want to edit "pre-fit" or "post-fit" residuals.  If you select "pre-fit", you can display the actual residuals on the C-file, as they would be passed to SOLVE for parameter estimation.  This mode of viewing is helpful when you are trying to detect a bad satellite or station in the solution and don't want its error to "smear" over into the residuals of other satellites or stations in the least squares adjustment.  More useful for editing, however, is the "post-fit" mode, in which CVIEW displays the residuals corrected ("flattened") as they are predicted to be after the parameter adjustments estimated by SOLVE are applied.  Thus, the post-fit mode can only be used after a solution has been run.  CVIEW uses these adjustments, along with the pre-fit residuals and partial derivatives from the C-files to compute "predicted" post-fit residuals according to the following formula:

			r' i  = ri + S  ( D pj • ∂ci/∂pj )
				  j=1,m

where	ri  is the prefit O – C ("observed – computed") at epoch i
	D pj is the adjustment to parameter pj
	∂ci/∂pj  is the partial derivative of the observation with respect to pj
	and m is the number of adjusted parameters

Finally, CVIEW will ask if you wish to read in one of the lists of rms values and cycle slips generated by SCANDD, sortv,  or SORTER.  An affirmative answer gives you the opportunity to go move quickly to the problematic double-difference combinations using the LIST command in CVIEW, as described below.  The filenames vscan.out and scan.out.worst are not currently included among the choices listed by CVIEW, but the file format can still be read—the user need only rename these files to cview.list. 

If you enter the M-file name as a command-line argument, you will get by default post-fit residuals for all of the C-files listed in the M-file.  In this case, the only question you will be asked is whether or not you wish to input a "list".  

As each C-file is read, header information is displayed, including parameters indicating the data types present.  Once all the C-files are read, CVIEW will display the first of several interactive menus used in plotting:

	L1	L2	LC	LG	WL	NO POLY	TIME SERIES	STACK[ ]	MOVIE[ ]	STOP

SEEK	PLOT	LIST	1-WAY	2 PRN06	3 PRN08	1 BLHL	2 VNDN	FILE	SEEK-FORW

For most of the boxes on the screen there is a stack of allowable commands, which can be selected by clicking on the box with the mouse.  The left button moves you backward in the stack, the right button moves you forward, and the center button selects the pre-programmed default shown in the illustration above.  The first four boxes in the top panel select up to five observables to be plotted.  The default  is plots of the L1, L2, LC, LG phase residuals and the wide-lane combination of phase and pseudo-range.  You can plot the receiver clock value, for example, by clicking on any of the boxes until CL appears. The complete list of allowable data types is given below in the order they appear in the menu stack:

AZ	azimuth from station to satellite (degrees, clockwise from north)
EL	elevation angle (degrees)
..	nothing plotted
L1	L1 phase
LG	geometry-free linear combination phase   (  L2  – g*L1 ) 
LC	ionosphere-free linear combination phase  ( 2.546 L1 – 1.984 L2 )
L2	L2 phase
P1	L1 pseudorange (cycles)
P2	L2 pseudorange (cycles)
WL	widelane combination (constant integer in cycles)
W*	widelane combination with large jumps removed (constant integer in cycles)
PG	geometry-free linear combination pseudorange  ( P2 - g*P1)
BG	 LG - PG  (cycles) 
I1	pseudorange ionosphere at P1  ( -g/(1-g2) PG )
I2	pseudorange ionosphere at P2  ( -1/(1-g2) PG )
CL	computed receiver clock correction (microseconds)
DT	horizontal display of all four one-ways in a double-difference combination

The sixth box in the top panel selects the order of polynomial to be removed from the plot, or the order of derivative to be taken.  For example, to plot the rate of change of double differences (akin to "triple differences") you would select DERIV 1  (the units are cycles per second), and to plot the derivative with a first-order polynomial removed, select D1 + P 1.  The most useful selections are P 1 and P 2, in connection with the SPAN command described below,.allow you to remove a first or second order polynomial from a short segment of data.  The next box selects TIME SERIES, SKY PLOT, or SPECTRUM, defining the type of axes to be drawn for the plot.  The next two boxes, STACK and MOVIE, allow you to stack a series of plots on the same screen and/or to cause them to be displayed automatically in sequence without intervention as explained below.  The brackets [ ] indicate that these two boxes are toggles, not stacks; clicking with any mouse button in the brackets introduces an asterisk [*] and turns on the feature.  The final box STOPs the CVIEW display and returns you to the control menu in the operating system window, at which point you can resume the display (and editing) or exit the program.  Returning to the operating system menu without exiting the program is useful if you need to check files or available disk space, for example.  

The bottom menu panel contains the satellite(s) and station(s) beling displayed.  The default is the first double-difference combination (as shown here), but you may display one-way or single-difference combinations by making the second box of one or both pairs blank.  Clicking on the fourth box (1-WAY) plots the one-way observable for the satellite and site shown in the first box of each pair.  As for the upper panel, the selection is changed by clicking on the box to rotate forward (right mouse button) or backwards (left button) in the stack.  The first three boxes on the left contain the commands allowing you to move from one screen to another. To change to a particular combination of satellites and stations, rotate (either backward or forward) to the selections in the right four boxes and click on PLOT.  To select the next available double difference, click (with any mouse button) on SEEK.  The default is to "seek-forward", in increasing order of satellites and stations, but you can reverse the process (e.g. to return to a problematic combination) by clicking on the last box to change SEEK-FORW to SEEK-BACK and then using SEEK

To move through the combinations on the input "list" file, click on LIST command with the middle button.  Clicking on LIST with the left or right buttoms will display in the bottom right corner of the screen the last or next combination, respectively, but will not plot it.  You can also use the  SEEK buttom to move through a list by changing the seek mode described above to SEEK-LIST

Finally, a hard copy of the screen plot may be obtained by clicking on FILE to write a file and then using the shell scripts skymap or xyplotc.

Time series are displayed with the mean removed and the value indicated to the left of the vertical axis as Y:  0 @ [mean value].  Also shown is the rms ("s") of the series about the mean.  The time (X-) axis is marked in hours and minutes (hh:mm) but without resetting to zero if the series goes over midnight.  Unless SHOW MARGINAL has been selected, the display will include only those observations weighted in the solution.  Continuous observations (no gap) are indicated by lines connecting each point.  The epoch number of any point can be displayed by clicking on the point.  The presence of an extra bias parameter is indicated by vertical bars, with "semaphores" attached to indicate (in single or double differences) which satellite(s) and station(s) have the bias flags; e.g.

							/
	|	station 1  satellite 1			|	station 2  satellites 1 and 2
	/						\

Stations are indicated by semaphores to the left (station 1) or right (station 2) (memory tool: stations are separated horizontally on the Earth); satellites by semaphores at the bottom (satellite 1) or top (satellite 2) (satellites rise or set vertically).  

When one or more time series are plotted on the screen, the top and bottom menu panels change to display the following:

SLIP [ ] 	MOVE	PATCH	FIND	SAVE	UNWT	REWT	BIAS (-/?/+)	UNDO	ELIM

SAVE	ABORT	SPAN[*]	ALL[ ]	<<T>>	>>T<<	MARG[ ]	HIDE[ ]	<<	>>

The boxes in the bottom panel (except for the first two) control the display of the plots.  The most useful command is SPAN.  Toggled on it automatically expands and contracts the horizontal axis to fit the time series being displayed.  Toggled on after selecting a range of points on the screen (by simply clicking on any of the displayed plots), it adjusts the horizontal scale to fit the span selected.  Toggled on after selecting a single point, it expands the scale and moves the selected point to the center of the screen.  ALL returns the horizontal scale to the complete interval of the session.  The next two boxes (<<T>> and >>T<<) directly expand or contract the time axis.  The final two boxes (<< and >>) move the origin to the left or right, expanding the time scale if appropriate.  For short (e.g., 225-point) series, the same effect can be accomplished with any one of several different selections of these six boxes.   The seventh box is a toggle between showing MARGINAL (unweighted) points and hiding them.  Toggled on [*], unweighted points are displayed as open circles or, if they were unweighted because they were below the elevation cutoff, as open squares.  At present CVIEW does not distinguish between slightly and grossly bad residuals, so that with marginals displayed the vertical scale is often distorted, masking variations in weighted points.  The HIDE box is a toggle between hiding bias flags that occur in one-way observations that fall in gaps in the double-difference combination being displayed (SOLVE will remember the flags and insert an extra bias parameter in the solution;  we term these "pushed" biases.)  ABORT quits the plot with no changes to the series; SAVE quits and saves any editing that has been done to that series.  

Most repairing of cycle slips is accomplished with the PATCH and MOVE selections of the top panel.  For either box, you must first select a single point in the series you wish to have moved to connect smoothly with the immediately preceding segment.  You do this by placing the cursor on the point and clicking with the left button on the mouse.  (The use of the middle and right buttons will invoke more powerful features, descibed below.)  Then, clicking on PATCH will cause the program to calculate automatically the number of cycles needed to repair the slip and to move selected point and all points beyond it.  If you have clicked on and L1 or L2 plot, PATCH will move the points in that plot only by the number of integer cycles that best connects the phase.  If you have clicked on LC, LG, or WL the program will calculate the number of L1 and L2 cycles necessary to best fit two combinations (with an appropriate weighting based on their respective scatters) and will display in the lower right corner the statistical confidence level of the fit.  Clicking on LC, invokes use of LC and LG; clicking on LG invokes use of WL (!) and assumes the change in LG = 0.; clicking on WL invokes use of WL and LG.  The PATCH algorithm is discussed further below in the context of editing strategies.  MOVE works only on L1 and L2 and allows you to adjust these series by integer or half-integer cycles using additional menu boxes that will appear:  

0.25	0.5	1	2	5	10	50	100	500	1000		Add 0.0

CANCEL  M	PERFORM  R

For each of the boxes of the top panel, clicking on the left mouse button will decrement (subtract from), and clicking on the right button will increment (add to), the value shown by the unit for that box.  Clicking on the middle button will choose the unit value.  The value selected will appear in the upper right corner of the screen (shown here as 0.).  Then clicking PERFORM or the right mouse buttom with the cursor in the plot area will execute the move; clicking CANCEL or the middle mouse button will cancel the selection.  The value of 0.5 is primarily for L2 with squaring-type receiver channels where a one-cycle slip in the original signal corresponds to a half-cycle in the displayed phase.  (The value of 0.25 [or 0.5 with full-wavelength signals] should be used sparingly and is included only to check for 180o phase shifts, usually temporary, of the signal in some receivers.)  MOVE is primarily useful to test for phase repairs when the visual impression implies a different number of cycles than the number calculated by PATCH.  Most of the time PATCH alone will do the trick. 

The BIAS box allows you to add (right mouse button), remove (left mouse button), or locate (center mouse button) extra bias parameters at epochs with questionable cycle slips.  It can be used with a single epoch or a range of epochs (the latter being useful primarily in removing bias flags).  ELIM will eliminate bias flags in all one-way data in series displayed unless a narrower span is defined by brackets.  FIND will attempt to assist you in locating the (one-way) satellite and station combination associated with a cycle slip or extra bias parameter following a gap by changing the display to put as the first satellite and station the one in which the gap occurred.  Clicking on SAVE or ABORT, followed by PLOT or SEEK will restore the original sequence.  (Be careful here, though, because you may end up using intervening commands that erase CVIEW's memory of the last combination.  It's a good idea to jot down on paper the combination on the screen before invoking FIND, so that when you're finished editing a particular epoch you can return to the right place in the search sequence. )  UNWEIGHT flags data points to be omitted from the solution by SOLVE; REWEIGHT removes the flag.  All of these commands are to be executed after you have selected a point or range of points on the screen by clicking on them with the mouse.  

Note that for double differences, the corrections you make are applied to the first satellite and first station displayed for the double-difference combination.  The importance of being aware of this feature is discussed in the next section.

The eighth and ninth boxes allow you to reverse your immediately previous action.  UNDO reverses the effects of PATCH, MOVE, WEIGHT, REWEIGHT, BIAS, and ELIM, all of the commands that actually change the data.  CANCEL simply removes the selection of points you have made in anticipation of a move.  The SLIP box is unused at present.

The MOVIE function is useful for viewing an entire set of residuals quickly to infer its character, locate a problem, or verify at the end of editing that everything is clean.  If STACK is invoked, all of the plots will be superimposed on the screen.  This is a powerful feature for discerning the nature of the residuals but it can become a mess if there are too many series.  Once you start the MOVIE, you can stop it by clicking anywhere on the screen with the middle mouse button (click once only and wait for the current frame to finish being written to the screen).  Following this by PLOT will show you the series that was on the screen when you stopped, allowing you to hit the panic button when you see something you don't like   If you start the MOVIE with the right button, plotting will stop at the first series with LC RMS > 1.0. 

When you have exercised all of the commands and gained some experience in data editing, you can use CVIEW in a more automatic mode, using the mouse buttons to reduce the number of hand motions required.  When the cursor is in the plot area of the screen, the mouse buttons take on different functions.  The left button puts brackets on the data as described above.  The middle button acts as SEEK or ABORT according to command displayed at the bottom.  The right button executes the sequence FIND + PATCH, with PATCHing being performed only if the correct satellite and station was "found"; a second click on the right button will SAVE and re-PLOT.  To UNDO the PATCHing, use the left button.

Fixing cycle-slips is straightforward if you remember certain rules.  If a particular receiver channel slips one or more  cycles, a break will appear in all data combinations that include that channel.  For example, a slip in the L2 phase at station 1 received from satellite 3 will appear in all double difference plots LC, LG, and WL that include station 1 and satellite 3.  The first step is to identify the station and satellite for which the slip occurred.  The best way to do this is usually with the printed or screen output of sortv or SORTER (from SCANDD).  You can also use the FIND command, however, to identify and display the station and satellite which had a gap or bias flag in the displayed double difference.  With this display, you can use PATCH (or MOVE) to fix the slip, and then return to the original order of the double difference combination by clicking on SAVE or ABORT.  If there is no gap or several gaps, then you should check all four one-way series.  Multiple slips are not uncommon since a satellite or receiver  may "hiccup", affecting multiple stations or channels, respectively.  In cases of very high noise in the one-ways (due to bad clocks or ionosphere), you may have to deduce the culprit channel by displaying several combinations of double differences.  For example, suppose that for three stations and three satellites the following combinations had a cycle-slip at a particular epoch of observation:

(station 1 - station 2) - (satellite 1 - satellite 3)
(station 1 - station 2) - (satellite 2 - satellite 3) 
(station 2 - station 3) - (satellite 1 - satellite 3) 
(station 2 - station 3) - (satellite 2 - satellite 3)  

It is clear that the cycle-slip occurred at station 2 and satellite 3.  Thus the  slip should be fixed with satellite 3 and station 2 appearing first when the double difference combination is selected in the menu.  In some cases the location of the cycle-slip is ambiguous.  For example, if only two stations are observing, it is impossible to determine at which site a slip occurred.  In this case, the slip can be fixed at either site,  The only requirement is that all double-difference plots be free of cycle slips, i.e, that the cycle-slips are fixed consistently.

Remember:  All  editing operations are applied only to the first satellite and station in the double difference combination, so if the the edit is made in double differences, you may have to switch the order before executing the operation (bias, unweight, reweight, patch, move)   

Once the correct satellite and station are identified as responsible for a cycle slip, the next step is to determine its size and whether it occurred in L1 or L2.  If the ionospheric fluctuation between epochs is much less than a cycle (or a half-cycle with codeless tracking channels), it will be obvious in the separate plots of L1 and L2 how many cycles slipped in each channel.   If the ionospheric fluctuations are large, however, only LC may be sufficiently smooth to discern the size of the slip.  In the most difficult cases, it may be necessary to examine all four phase series (L1, L2, LC, and LG) to deduce the combination of L1 and L2 cycles (and/or half-cycles) responsible for the LC jump.  Table 6.1 gives the most common residual LC and LG jumps that occur for combinations of slips in L1 and L2 for the cases of full-wavelength and half-wavelength L2.  The bold-faced entries, representing LC jumps of less than one cycle, are the most dangerous since they can escape detection if the fluctuations in L1 and L2 due to the ionosphere are very large.

Using PATCH in CVIEW allows you to avoid computing the L1 and L2 combinations explicitly.  Used with LC or LG, PATCH will make a best estimate of the jumps by examining these two time series and apply integer corrections to L1 and L2.  The statistical confidence of the estimate is displayed, allowing you to assess whether to retain or add a free-bias flag at the break.  This is a useful feature even when you believe that there is no slip, in order to reinforce your subjective judgement of the confidence of the connection made by AUTCLN, SINCLN, or DBLCLN.  PATCH uses up to 15 points on either side of the slip (usually also a gap) in estimating its correction.   Its estimate and confidence level are reliable as far as the LC and LG residuals are concerned.  There are times, however, when the analyst is justified in raising the confidence level based on the appearance of L1 and L2.  If LC and LG are noisy compared with L1 and L2 (which can occur if multipathing dominates ionospheric fluctuations), then using PATCH or MOVE on L1 and L2 separately is more convenient.  In this case Table 6.1 is particularly useful.

Table 6.1	LC and LG jumps for L1 and L2 slips
LC = 2.546 L1 - 1.984 L2		LG = L2 - 0.779 L1
	L1	L2	LC	LG
All combinations £ ± 1 
	-1	-1	-0.56	-0.22
	-1	-0.5	-1.55	0.28
	-1	0	-2.55	0.78
	-1	0.5	-3.54	1.28
	-1	1	-4.53	1.78
	0	-1	1.98	-1.00
	0	-0.5	0.99	-0.50
	0	0.5	-0.99	0.50
	0	1	-1.98	1.00
	1	-1	4.53	-1.78
	1	-0.5	3.54	-1.28
	1	0	2.55	-0.78
	1	0.5	1.55	-0.28
	1	1	0.56	0.22
Positive combinations £ ± 5 with LC < 1.0 or LG<0.1
	2	1.5	2.12	-0.06
	2	2.5	0.13	0.94
	2	3	-0.86	1.44
	3	4	-0.30	1.66
	4	5	0.26	1.88

In data sets with many gaps, there may be a large number of bias flags inserted by SINCLN (using one-ways and single differences) in places where, from double differences, you are confident of continuity.  In this case, you can use the BIAS function to remove all bias flags which are in the first satellite and station displayed or the ELIM function to remove bias flags in all satellites and stations associated with the series.  If a data set has many small gaps but few actual cycle slips, it is sometimes easier to remove all the bias flags before starting and then add back the ones you need.  This strategy is facilitated by program RMBIAS, which is run from a batch file ( rmbias.bat ).  To create this batch file run the script mk.rmbias, responding to the prompt with the 6th character of the input C-files.  The script will then create in rmbias.bat an RMBIAS command for each C-file in your directory with that 6th character.  The output C-files will always have 6th character "x".  You can rename them using the scripts mvcf or copyc.  If you are using AUTCLN, there should never be a large number of bias flags remaining and you should have no need for RMBIAS. 

After you have completed all editing for the session, click on STOP and answer positively the query to write out corrected C-files.  The names of the new C-files are created by incrementing the sixth character of the old C-file names. Whenever you select STOP while editing, CVIEW will give you the opportunity to continue editing and/or to save the edited C-files by issuing the following prompt:

You may:
	1	Write new C-files, incrementing series letter
	2	Write new C-files, incrementing series letter and deleting old C-files
	3	Overwrite input C-files
	4	Not write any C-files
	5	Not write any C-files but save vcview.out

Only 1 and 4 will let you continue editing

Pick a number

If you have set up a "quick" plus regular batch processing sequence (1-ITER) and omitted (commented out) AUTCLN, SINCLN, or DBLCLN, then in your first pass through CVIEW you should increment the series letter  (i.e., cssssa.ddd becomes cssssb.ddd) by selecting option 1 or 2.  If you have already incremented the series letter and want to edit "in-place", then you would select option 3.  If you wish to continue editing or exit without updating the C-files, select option 4.  If you select options 1 or 4, you will get the prompt

Do you wish to continue editing (Y/N)

A "yes" (Y) reply will return you to the editing screen, after performing an interim save of the C-files if you have chosen option 1.  A "no" (N) reply will exit the CVIEW, either directly if you have selected option 4, or after writing out the C-files if you have selected option 1.  When you are engaged in a long editing sessions, it is prudent to STOP editing periodically to save the C-files.  (Neither the hardware we have used nor the software we have written is immune to unexpected crashes.) 

Note that if you change your mind after saving C-files about the series letter you wish to retain, you can use the shell script  mvcf (or copyc to rename or replace all of the C-files in your working directory:
			mvcf   b  a

will rename cssssb.ddd  to cssssa.ddd, replacing old cssssa.ddd files if they exist.  

Option 5 at the end of editing will write out a file (vcview.out) of all the edits you have made in the session.  Running the (interactive) program AUTEDT or the shell script sh_autedt extracts from vcview.out the information about which data you have unweighted and appends to the autcln.cmd file the appropriate commands for AUTCLN. 

6.5 Strategies for Editing

The most efficient strategy for editing a data set depends strongly on the size of the network and the quality of the data.  For local networks of only a few stations, and particularly with short observation spans, viewing all of the data with CVIEW and peforming manual editing is advisable to recover correctly all of the available observations.  For larger networks and 24-hour obsrevations spans, however, little if any manual editing should be required.  With appropriate controls AUTCLN can recover a data set that will produce parameter estimaes insignificantly different from those resulting from a 'perfect' edit, and in fact will usually do a better job than the analyst.  

The preferred stategy for networks with more than two or three stations is to examine the outputs of SOLVE (q-file), AUTCLN (autcln.sum), and SCANDD (sorted versions of vscan.out and scan.rms) to determine if there were any problems with the run, then use CVIEW to identify station or satellite and cause of the problem.  With the deletion of problematic data, AUTCLN can almost always produce a slip-free series of observations, so we prefer not to perform any manual edits in CVIEW, but rather to rerun AUTCLN with instructions to unweight the bad or difficult data.  This approach has two advantages:  1) it transfers the burden of editing from the (expensive, slow, and fallible) analyst to the (cheap, fast, and slightly less fallible) cpu;  2) the autcln.cmd file now maintains the record of all edits, so that you can reprocess the data, from RINEX files if necessary, as modeling and editing algorithms improve.  

The most obvious indicator of a bad solution is the nrms value in the q-file.  As discussed in Section 5.5, values above 0.3 usually signify a problem, and for many surveys you should expect most values to be near 0.2.  If you are processing several days of a survey at one time, grep'ing on 'nrms' for all of the q-files will give you an indication of problem days.  If the nrms is abnormally high, you should then look at the scan.rms output of SCANDD (or rms.ful after running SORTER) to see if a single satellite or station is causing a problem.  If you find values greater than about 0.2 cycles, you should examine the residuals visually with CVIEW to understand the cause of the problem.  

Even without a high nrms, you should examine the autcln.sum file to ascertain whether there are problems with a station or satellite.  If a receiver or clock is malfunctioning, or if you have a bad a priori coordinate for the station, AUTCLN may have deleted large quantities of data or added an excessive number of bias flags.  The first three tables in the summary file will tell you quickly if there is a problem.  The most definitive check is to make sure that in the DATA AMOUNTS listing there are small numbers in the Gap (data deleted in gaps) and BF (bias flags remaining) columns and that the number of data retained (Good column) are comparable to those for other stations.  If you find anomalies, the other tables in the file and CVIEW can help you determine the source of the problem.  (See the explanation for these tables in sections 6.2 and 7.6 and the on-line help for AUTCLN.)

Finally, as a check for residual cycle slips you should run sortv on the vscan.out file from SCANDD.  Usually, looking at vxxxx1.ddd.worst will tell you if there are any potential slips.  It would be unusual for there to be more than one or two of these (if any) after AUTCLN unless there is a station with a malfunctioning receiver.  

For regional networks, there is one additional and very important editing consideration if you plan to attempt ambiguity resolution in the analysis.  The present version of SOLVE assigns the (one allowed) explicit ambiguity parameter to the last segment of the double-difference series; that is, the data after the last extra bias parameter (shown by a bar in CVIEW).  This is because the extra bias parameters are all estimated implicitly.  In order to maximize the probability that the ambiguity for a series will be resolved, you want to have the last segment as long as possible.  This means that for stations in a regional network you should not leave an extra bias parameter in the latter part of an otherwise continuous series, but rather unweight the data at the end containing these extra biases.  The last entry in the trim_oneway_tol command for AUTCLN gives you some control over this, but it's still possible to have a too-short segment at the end of a double difference sequence.  For widely spaced fiducial stations where there is no chance to resolve ambiguites, leaving an extra bias parameter associated with a few points at the end is of little consequence.  The important thing in this case is to avoid breaking up with bias flags long segments of data, wherever they are located in the observing span.

Once you have identified any editing problems with the solution, you should make take appropriate action and then rerun the solution from the appropriate step.  If the problem is bad data from station or satellite you can begin with AUTCLN, after removing the bad data  from consideration using the edit_site_sv command in the autcln.cmd file (taking advantage of CVIEW's ability to generate these entries automatically for short segments removed using the UNWT command).  If the problem is a bad a priori station coordinate or satellite orbit, you should begin with MODEL after updating the L- or T-file.  Occasionally the appearance of bad data can be traced back to a problem with the information in the RINEX file (e.g., named incorrectly) or the auxilliary files of GAMIT (UT1., pole., station.info ).