[IGSMAIL-2879]: new <P1-C1> pseudorange bias corrections

Fri Jun 9 05:53:41 PDT 2000

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IGS Electronic Mail      09 Jun 05:53:25 PDT 2000      Message Number 2879
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Author: Jim Ray

Dear Colleagues,

With reference to the <P1-C1> pseudorange bias values distributed in IGS
Mail #2744 (15 Mar 2000), David Jefferson (JPL) has computed an updated set
of biases using the same procedures as Ron Muellerschoen did for the
previous set; see the attached e-mail below.  These biases are based on
Ashtech Z-12 data only, collected after the launch of the new Block IIR
satellite PRN20/SVN51, which has been added, and the decommissioning of
PRN14, which as been dropped.  As before, the biases have been renormalized
to zero mean across the constellation in order to leave the net receiver
clock bias unaffected.

The following set of new <P1-C1> bias values is recommended for use by all
IGS Analysis Centers and users of IGS clock products, preferably starting
with data collected on 18 June 2000 (beginning of GPS week 1067):

    average <P1-C1> biases (mm) in PRN order:

    -76  -261    74   508  -174   209  -272  -157   124  -464     PRN01-10
    -11         549        -316  -185  -228    83    81  -256     PRN11-20
   -137  -450  -148   180   206   463     4         281   560     PRN21-30
   -187                                                           PRN31-40

As described by David (see below), these new biases differ from the previous
set by 34 mm (RMS), with minimum and maximum changes of -73 and 89 mm,
respectively.

The RINEX converter utility, cc2noncc, has been updated accordingly.  This
utility can be used to transform AOA TurboRogue, AOA ICS-4000Z, and Trimble
4000 RINEX files to be compatible with modern receiver types.  The Fortran
code is available at ftp://maia.usno.navy.mil/pub/biases/cc2noncc.f
(version 1.4, 08 Jun 2000).

--Jim Ray

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Date: Thu, 8 Jun 2000 15:11:57 -0700 (PDT)
From: David C Jefferson <djeff at cobra.jpl.nasa.gov>
To: jimr at maia.usno.navy.mil
Subject: Latest C1-P1 results
Cc: David.Jefferson at jpl.nasa.gov, James.F.Zumberge at jpl.nasa.gov,
        Ronald.J.Muellerschoen at jpl.nasa.gov, Yoaz.Bar-Sever at jpl.nasa.gov,
        gpetit at si.bipm.fr, tim.springer at aiub.unibe.ch

I have been assisting Ron Muellerschoen in reviewing our P1-C1 estimates.
My comparisons involve our original estimates based on Ashtechs only, new
estimates based on Ashtechs only, new esimates based on Benchmarks only,
and Ashtech/Benchmark estimates from Y. Gao at the University of Calgary.

After adjusting each of the sets of satellite-dependent pseduorange biases
to make them consistent (w.r.t. sense, zero-means, satellites used, and
reference used), the following statistics have been realized using 25 GPS
satellites (units are mm):

          n        mean        sd        min        max        RMS        med
 GB-GA:  25          0         82       -177        140         80         25
 JA-JA0: 25         -1         35        -73         89         34          1
 JB-JA0: 25          0         96       -241        195         94         11
 JB-JA:  25          1         96       -238        157         94         14
 JA-GA:  25         -1         38        -99         68         37          7
 JB-GB:  25          0         57       -131        104         56          2

KEY: GA  = Gao Benchmark estimates
     GB  = Gao Ashtech estimates
     JA0 = original JPL Ashtech estimates
     JA  = recent JPL Ashtech estimates
     JB  = recent JPL Benchmark estimates

Our results are consistent with those from Gao, in that:

 a) Ashtech then/now agreement is about 3 cm (Gao = 1 cm).
 b) RMS difference between Ashtechs vs. Benchmarks is about 9 cm (Gao = 8 cm).

We also now have (Ashtech) estimates for newly-lauched PRN20/GPS51.  A full
full of new estimates, which we expect to incorporate into our processing
shortly, is shown below:

    -76  -261    74   508  -174   209  -272  -157   124  -464     PRN01-10
    -11         549        -316  -185  -228    83    81  -256     PRN11-20
   -137  -450  -148   180   206   463     4         281   560     PRN21-30
   -187                                                           PRN31-40

We also intend to asses the effects of using our Benchmark estimates, alone
as well as with the Ashtech ones, on our global network orbit analyses.
Please forward this message as appropriate.

Regards,
David