[IGSMAIL-1119] SOPAC Orbits

[P.]

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IGS Electronic Mail      Mon Nov 20  8:49:38 PST 1995      Message Number 1119
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Author: P. Fang, P. Tregoning, and Y. Bock
Subject: SOPAC Orbits 

Scripps Orbit and Permanent Array Center (SOPAC)
Date: November 20, 1995

Subject: Update on SOPAC Rapid and Predicted Orbits Service

To support a wide range of geophysical and meteorological research
activities using GPS technology, including early earthquake response
for the southern California continuous GPS array (SCIGN/PGGA), 
in-the-field processing for the University NAVSTAR Consortium (UNAVCO),
and near-real time precipitable water estimation for the U.S. CORS
network, we have upgraded our rapid and predicted (extrapolated) orbit
service, effective immediately.  

Note: 
  Final precise orbits are available with a delay of about 7 days with
  a precision of 8-11 cm.  These are contributed to the rapid and final
  orbit products of the International GPS Service for Geodynamics (IGS).
  The computation of these orbits is delayed to allow data from sites
  which may have been slow in being made available to the IGS analysis
  centers to be included in the solutions. The IGS combined rapid orbits
  are available from the IGS Global Data Centers within 7-10 days of
  data collection with a precision approaching 5 cm.

Our rapid service provides the following products:

1. Precise orbit determination with 14-18 hours delay from end of IGS
   data collection epoch (24 h UT), with a precision of 15-20 cm rms.

2..Predicted orbits available at about 1800 UT on the current day
   for which they are valid, that is 6 hours before IGS daily data
   collection end, or 6 hours in real time. The precision of these
   predicted orbits is 40-80 cm RMS. The predicted orbit provides an
   ephemeris for a particular day up to 20 hours earlier than the first
   SIO computed precise orbit spanning the same period.  We are 
   currently experimenting with an orbit that is fully available in
   real time.

3. Pole position estimates with 14-18 hours delay as per item 1, with a
   precision below 0.5 mas for both X and Y components and an offset of
   0.1 mas in X and 0.4 mas in Y when compared with IERS Bulletin A.

The above products are available on our anonymous ftp server (see below)
under:

Items 1 and 2:   combination/wwww

Item 3       :   products/wwww

Final Orbits :   products/wwww

where wwww is the GPS week number. All orbit products are available in
NGS SP3 format and pole position estimates are in free format. The file
naming convention is as follows:

sipwwwwd.sp3     -  predicted orbit

sirwwwwd.sp3     -  rapid precise orbit

siowwwwd.sp3     -  final precise orbit

siopoleut.rapid  -  pole estimates

Notes:

(1) NGS SP3 format  (e.g., sioWWWWd.sp3) is the recognized orbit
exchange format adopted by the IGS.

(2) To access SOPAC GARNER archive:
    ftp toba.ucsd.edu (132.239.152.80)
    login: anonymous
    password: your e-mail address
    Direct problems to: pgga at pgga.ucsd.edu
    Geodesy Lab Tel: +1 619 534-7692
    Fax: +1 619 534-9873
    WWW Home Page - http://toba.ucsd.edu

(3) The siopoleut.rapid file contains UT values. These are NOT 
    estimated values, they are IERS Bulletin A predicted values.

(4) SIO uses GAMIT/GLOBK software which has recently undergone much
    development.  Thanks are extended to Bob King, Tom Herring and
    Simon McClusky (MIT) for their efforts in this regard.

Disclaimers:

(1) These SOPAC products are intended for near-real time scientific, 
non-commercial applications. They are not intended to replace the
official IGS rapid orbit. 

(2) Due to the automatic nature of these products, SOPAC is not
responsible for their accuracy, reliability and availability.
However, all care will be taken to maintain the accuracy of the
products.


[Mailed From: pgga at pgga.UCSD.EDU (Geodesy Lab account)]