Appendix 5.  Scripps Orbit and Permanent Array Center

The Scripps Orbit and Permanent Array Center (SOPAC) is located at Scripps Institution of Oceanography at the University of California, San Diego.  One of its activities is the computation of precise satellite ephemerides and earth orientation as one of the seven IGS  Analysis Centers.  SOPAC is also one of three Global Data Centers for the IGS and maintains an on-line archive of RINEX data for the growing number of global GPS tracking stations.  Finally, SOPAC operates the Permanent GPS Geodetic Array (PGGA), a widely distributed component of the Southern California Integrated GPS Network (SCIGN), and archives data from continuously tracking GPS stations in California and the Continuously Operating Reference Station (CORS) Network throughout the U.S.  Though many of SOPAC's products are in standard IGS formats and useable by a variety of software packages, some are of particular value to GAMIT/GLOBK users. 

SOPAC products for GAMIT/GLOBK Users

Precise ephemerides (g-files)

SOPAC computes daily, precise satellite ephemerides with GAMIT using 24 hours of data (0-24h UT) from approximately 45 tracking stations of the IGS.  The so-called rapid solution is initiated at 1245 UT of the following day and the orbit is generally available by about 1600 UT in two ASCII formats:

(1) GAMIT G-file format, e.g., gpggaY.DDD.rap.  This short file contains initial conditions for all GPS satellites at 12:00 UT and can be used with ARC to produce a T-file for GAMIT processing.

(2) NGS SP3 format, e.g., sirWWWWD.sp3, where WWWW is the GPS week number. This file of Earth-fixed positions can be converted to a best-fit T-file using the shell_script sh_sp3fit (see Chapter 4). 

In addition, a 24-hour predicted orbit is computed from a three-day GAMIT solution.  For present day x, the initial conditions for day x-2 are estimated from data obtained on days x-3 through x-1 and integrated forward.   The predicted orbit is generally available by 1600 UT of the day for which it is valid. It is posted in the same two formats as the rapid orbit— GAMIT G-file and NGS SP3.

The standard SOPAC analysis for the IGS proceeds with about a 3-4 day lag.  Orbits are submitted to the IGS after the entire GPS week is completed.

To summarize the available orbits and naming conventions:
• sipWWWWD.sp3/gpggaY.DDD.pre = SOPAC predicted orbit
• sirWWWWD.sp3/gpggaY.DDD.rap = SOPAC rapid orbit
• sioWWWWD.sp3/gpggaY.DDD,  sioWWWW7.sum = SOPAC's weekly GLOBK summary file 

Example naming of final SOPAC products:
sio07957.sum	weekly summary file.
sio07957.erp	Polar motion parameters for GPS week 0795.
sio0795[0-6].sp3	Daily ephemerides for GPS week 0795, SP3 format [0=Sun, 6=Sat]

The rapid and predicted ephemerides are posted to the combination/WWWW directories as they become available.  SOPAC's final, precise ephemerides are posted to the products/WWWW directories when the GLOBK for the entire GPS week has been run.

In addition to the final products from the SOPAC processing, predicted and final SP3 files from other IGS analysis centers are posted in products/WWWW.  For example, 
igsWWWWD.sp3 is the IGS official orbit computed from the orbital information submitted by all seven Analysis Centers and available with about a 10-day lag. 

Caution:  Please scan the .sum files before using a particular orbital day.  Look for any satellites that have large overlap errors, or for remarks that indicate that a particular satellite has a problem.

ASCII h-files

Compressed ASCII H-files for the loosely constrained, global and regional GAMIT solutions, including parameter slots for station coordinates, satellite initial conditions, and earth orientation are kept on-line for combination with H-files obtained from regional solutions.   The directories are  hfiles/YYdata/PROJ, where PROJ is one of six types:  igs[1 or 2], pgga, dgga, cors, eura or indo, where type corresponds to a sub-network of the SOPAC solution.  Generally, you will want to combine your regional solution with only the two global H-files, higs1.ddd.Z  and higs2.ddd.Z

Earth Orientation Parameter Tables

A current set of EOP tables in GAMIT format can be found on pgga.ucsd.edu (login: anonymous; passwd: email address) under pub/gamit/tables as ut1.usno and pole.usno.  A script (sh_update_eop) is available in the same directory (and also in the /com directory of the MIT GAMIT distribution) which will ftp the current files from SOPAC and update your pole. and ut1. tables.

Miscellaneous Information

• UNIX scripts for converting between [GPS week, day of week] & [year, day of year] and [Calendar date] & [year, day of year].

directories: docs/utilities [named gweek & jday, respectively]

• Station and antenna information:

a) station.info:  History of site occupations at IGS, SCIGN and CORS sites, including receiver codes, antenna codes & heights, firmware versions, comments, etc.  This file is kept as station.info.sio in docs.

b) itrf93_1995_iers:  ITRF93 station coordinates (reference frame).

c) site logs:  IGS format site logs containing site information and equipment deployment history for sites archived by SOPAC are kept in docs/site_logs.

d) additional files as needed and requested can be found in docs/sites_antennae

• SOPAC RINEX holdings:

SOPAC Archive newsletters indicating the RINEX data available on the archive at the time of issue, approximately 4 days after the end of each GPS week.  Files of the form WWW.letter are located in docs/newsletter.

SOPAC Archive Access

Access the SOPAC Garner Archive using anonymous ftp:
   ftp toba.ucsd.edu (132.239.152.80)
   login: anonymous
   password: your email address

Direct problems to: pgga@pgga.ucsd.edu

You may also visit the SOPAC WWW homepage at http://toba.ucsd.edu to check data availability and to submit requests for off-line data.

SOPAC personnel and address

Yehuda Bock, Jeff Dean, Peng Fang & Rosemary Leigh
Institute of Geophysics and Planetary Physics (IGPP)
Scripps Institution of Oceanography (SIO)
9500 Gilman Dr.
La Jolla, CA 92093-0225 USA
e-mail: pgga@pgga.ucsd.edu
Geodesy Lab telephone: (619) 534-7692
FAX: (619) 534-9873

SOPAC is not responsible for the accuracy/reliability/availability of its data and products.