[IGSMAIL-2235] AMC2 RINEX procedures and observables

[Jim]

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IGS Electronic Mail      Wed Apr 14  5:47:17 PDT 1999      Message Number 2235
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Author: Jim Ray
Subject: AMC2 RINEX procedures and observables

On 08 March 1999, the AMC2 receiver at Schriever Air Force Base, Colorado
Springs, CO, USA was changed from an AOA ROGUE SNR-12 (s/n T245) to a
retrofitted AOA SNR-12 ACT (s/n 247-U), which is functionally equivalent
to an AOA BENCHMARK ACT receiver -- see IGS Mail #2198 (10 March 1999).

Beginning 16 March 1999, the data download procedures for AMC2 were 
changed to use TurboBinary offload files with RINEX translation done by
"teqc -aoa tbY".  As described by Herb Dragert in IGS Mail #2234
(12 April 1999), the AMC2 (AOA SNR-12 ACT) observables are now:
           C1      = C/A code at L1 freq.
           L1(C1)  = C/A-based phase at L1 freq.
           P1      = Y1-codeless pseudorange at L1 freq.
           P2      = Y2-codeless pseudorange at L2 freq.
           L2(P2)  = Y2-codeless-based phase at L2 freq.

These differ significantly from the TurboRogue-style cross-correlation
observables:
           C1      = C/A code at L1 freq.
           L1(C1)  = C/A-based phase at L1 freq.
           P2'     = codeless pseudorange at L2 freq.
           L2'     = cross-correlated phase at L2 freq.
because the P2' pseudorange-type observable and the L2' phase are actually
formed by a process which tracks the cross-correlated (P2-P1) pseudorange
and the (L2-L1) phase differences:
           P2' = C1 + (P2-P1)
           L2' = L1(C1) + (L2(P2)-L1(P1))

Users of AMC2 data should be aware that the new pseudorange observable
pair (P1, P2) differs from the usual TurboRogue-style pseudorange pair
(C1, P2') by (C1-P1) biases which are not zero-mean and can reach up
to +/- 2 ns.  Because the biases are satellite-dependent and receiver-
dependent, they are not removed by double differencing.  There is no
significance for data analysts who process only the carrier phase
observables.

NOTE: An IGS-wide approach to handling a mix of TurboRogue-style and
non-TurboRogue data will be considered at the IGS Analysis Center
Workshop at SIO in June.

=========================================================================
Jim Ray                                   e-mail: jimr at maia.usno.navy.mil
U.S. Naval Observatory, EO Dept.          phone : 202-762-1444
3450 Massachusetts Avenue, NW             fax   : 202-762-1563
Washington, DC  20392-5420
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[Mailed From: Jim Ray (USNO 202-762-1444) <jimr at maia.usno.navy.mil>]