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[IGSMAIL-3160]: updated <P1-C1> pseudorange bias corrections



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IGS Electronic Mail      05 Jan 06:11:04 PST 2001      Message Number 3160
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Author: Jim Ray

Dear Colleagues,

With reference to IGS Mail #2879 (09 Jun 2000) and previous messages on the
handling of <P1-C1> pseudorange bias values, I propose a somewhat different
strategy for updating biases.  Updated values are needed now because of the
addition of the new satellites PRN28 (Aug 2000) and PRN14 (Dec 2000), and
the decommissioning of PRN16 (Jul 2000) and PRN18 (Jun 2000).

The current IGS <P1-C1> bias values were determined by David Jefferson (JPL)
based on Ashtech Z12 data only.  Since then, direct estimates of the biases
from a mixed network of cross-correlation style and non-cross-correlation
receivers have become available as a standard byproduct of the ionospheric
analysis made by Stefan Schaer; see IGS Mail #2827 (09 May 2000) and the web
site at <http://www.aiub.unibe.ch/ionosphere.html>.  A set of <P1-C1> biases
is maintained automatically based on a 7-day moving average of the latest
bias estimates from the CODE clock analysis procedure.

For the following reasons I propose that Stefan's <P1-C1> bias values be
adopted for use with the IGS official products: 1) his estimates are
continuously and automatically updated which eases future IGS updates;
2) his bias values are estimated directly from the data sets for which they
will be applied (i.e., mostly TurboRogue receivers); 3) the CODE analysis
includes a large number of receivers, usually a superset of those used by
other Analysis Centers, and does not explicitly rely on any particular
receiver models.

Consequently, 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 14 January 2001 (start of GPS
week 1097).  (These are the 7-day averages posted by Stefan on 26 December
2000.)

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

    222  -546    42  1294  -798   625  -523  -193    48 -1002     PRN01-10
   -329        1545  -409  -755        -522         582  -958     PRN11-20
   -172 -1374 -1018   459   775  1077   213  -144   611  1745     PRN21-30
   -496                                                           PRN31-40

NOTE THE CHANGE IN UNITS FROM mm BEFORE to ps NOW!   1 mm  = 3.3356410 ps

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 2.0, 04 Jan 2001).

--Jim Ray