[IGSMAIL-6583] GPS quarter-cycle biases

[Stefan Schaer]

Author: Stefan Schaer and Michael Meindl


Dear IGS colleagues,

Until recently, we did expect GPS quarter-cycle biases between L2(P)
and L2(C) only for Leica and NovAtel receivers. As a consequence,
ambiguity resolution was not permitted between modernized GPS
satellites (specifically Block IIR-M and IIF) and older generations as
soon as a receiver type belonging to the mentioned receiver group gets
involved.

We could recognize, however, three additional characteristics that must
be taken into account:

1. Javad receivers obviously also belong to this receiver group
(potentially revealing quarter-cycle biases). We could verify
corresponding biases for the JAVAD TRE_G3TH DELTA receivers operated at
AREV, DGAV, TABV, WTZZ. It is worth mentioning that AREV, DGAV, TABV
started to provide C2 and thus implicitly L2(C) on February 3, 2012.
Quarter-cycle biases started to occur exactly in coincidence with that
date (day 034 of 2012) for these Javad receivers.  Verification was
possible on the zero baselines AREV-AREQ (wrt ASHTECH UZ-12), DGAV-DGAR
(wrt ASHTECH UZ-12), and ultimately on the 50km baseline TABV-JPLV (wrt
JPS EGGDT).

2. Moreover, we realized that there are certain time periods for
particular modernized GPS satellites where C2 and L2(C) seem to be
commonly unavailable (no receiver model was able to provide C2 and
L2(C) at all). SVN49 is a prominent candidate in the table of such time
periods:

PRN01/SVN49: 54951 <= MJD < 54970
PRN25/SVN62: 55353 <= MJD < 55375
PRN01/SVN49: 55677 <= MJD < 55688
PRN24/SVN49: 55959 <= MJD < 56001

3. Finally, we noticed cases, where L2(C) was not observed by
particular receivers for one (or a subset) of the modernized GPS
satellites.

As a consequence of the above observations, we changed our analysis
software in a way that ambiguity resolution is generally not permitted
between modernized GPS satellites as soon as a Javad, Leica, or a
NovAtel receiver type gets involved.

For completeness, an updated list of receivers for which GPS L2
quarter-cycle biases may occur is appended:

AREV: JAVAD TRE_G3TH DELTA 3.3.2                G:C1 G:P1 G:P2 G:C2 G:C5
CONZ: LEICA GRX1200+GNSS   8.51/6.110           G:C1 .    G:P2 G:C2 G:C5
DGAV: JAVAD TRE_G3TH DELTA 3.3.5                G:C1 G:P1 G:P2 G:C2 G:C5
HYDE: LEICA GRX1200GGPRO   7.53/3.019           G:C1 .    G:P2 G:C2 .
ILHA: LEICA GRX1200GGPRO   8.00                 G:C1 .    G:P2 G:C2 .
KAT1: LEICA GRX1200+GNSS   8.20/4.007           G:C1 .    G:P2 G:C2 G:C5
LAMA: LEICA GRX1200+GNSS   8.10/4.007           G:C1 .    G:P2 G:C2 .
M0SE: LEICA GR25           2.50/6.110           G:C1 .    G:P2 G:C2 G:C5
MAC1: LEICA GRX1200+GNSS   8.10                 G:C1 .    G:P2 G:C2 G:C5
OHI3: LEICA GRX1200+GNSS   8.20/4.007           G:C1 .    G:P2 G:C2 G:C5
TABV: JAVAD TRE_G3TH DELTA 3.3.3                G:C1 G:P1 G:P2 G:C2 G:C5
TORI: LEICA GRX1200+GNSS   8.10/4.010           G:C1 .    G:P2 G:C2 .
UNBN: NOV OEMV3            3.901                G:C1 .    G:P2 G:C2 .
VALA: LEICA GRX1200+GNSS   8.20/4.007           G:C1 .    G:P2 G:C2 G:C5
WROC: LEICA GRX1200GGPRO   8.51/3.019           G:C1 .    G:P2 G:C2 .
WTZR: LEICA GRX1200+GNSS   8.10/4.007           G:C1 .    G:P2 G:C2 G:C5
WTZZ: JAVAD TRE_G3TH DELTA 3.3.8 MAR,20,2012    G:C1 G:P1 G:P2 G:C2 .

Best regards,

The CODE AC Team