[IGSMAIL-0851] SOPAC Rapid Orbits

[Yehuda]

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IGS Electronic Mail      Fri Jan 20 12:59:28 PST 1995      Message Number 0851
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Author: Yehuda Bock and Peng Fang
Subject: SOPAC Rapid Orbits 

Scripps Orbit and Permanent Array Center (SOPAC)
Date: January 20, 1995
Subject: SOPAC Rapid Orbits

To support early earthquake response and near-real time analysis
for the southern California continuous GPS array (SCIGN/PGGA),
we have begun to compute and post rapid GPS ephemerides.

We automatically process all available global IGS data at 17:00 UT
of the following day. This process is completed by 22:00 UT. We post
the rapid orbits at around 24:00 UT in two ASCII formats:

(1) GAMIT g-file format, e.g., gpgga5.020.rap. This short file contains
initial conditions for all GPS satellites at 12:00 UT.  This file can 
then be integrated with the GAMIT ARC program to produce an internal GAMIT
orbit.

(2) NGS SP3 format, e.g., sirWWWWd.sp3.  This is the recognized orbit
exchange format adopted by the International GPS Service for
Geodynamics (IGS).

In addition, we compute a 24-hour predicted orbit from the rapid orbit
described above so that it is available in real time. It is posted in
the same two formats.

Our standard analysis for the IGS proceeds as before with about a 3-4
day lag. We submit to the IGS after the entire GPS week is completed.

To summarize the available orbits and naming conventions:

sipWWWWd.sp3/gpggaY.DDD.pre = predicted, are replaced by rapid orbits
	as soon as next day's rapid orbit is generated.

sirWWWWd.sp3/gpggaY.DDD.rap = rapid, are replaced by GAMIT daily series
	as soon as the daily solution is completed.

sidWWWWd.sp3/gpggaY.DDD.gam = daily, are replaced by GLOBK weekly series
	as soon as the weekly solution is completed.

sioWWWWd.sp3/sioWWWW7.sum, gpggaY,DDD = GLOBK weekly + summary file

igsWWWWd.sp3 = IGS official orbit

WWWW = GPS week; DDD = day of year; Y = last digit of year

To access these orbits:

To access orbits on SOPAC GARNER archive:
 ftp toba.ucsd.edu (132.239.152.80)
 login: anonymous
 password: your name
 directories: products/wwww (wwww = GPS week number)
Direct problems to: oral at pgga.ucsd.edu

These rapid orbits are intended for near-real time scientific
applications. They are not intended to replace the official IGS
orbit distributed currently with a delay of about 10 days.

Initial tests indicate good precision for baselines computed
with these orbits. Further details will follow.

Due to the automatic nature of the rapid orbits, SOPAC is not responsible
for their accuracy/reliability/availability.


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