Bernese GPS Software Version 5.0 - Bernese GNSS Software

13.2 How to Correct P1–P2 and P1–C1 Code Biases
Table 13.1: Corrections due to satellite-specific P1–P2 and P1–C1 code bias values for the
most important linear combinations (LC) derived from various combinations
of code observable types.
LC P1/P2 C1/X2=C1+(P2−P1) C1/P2
L1 +1.546·BP1−P2 +1.546·BP1−P2 +BP1−C1 +1.546·BP1−P2 +BP1−C1
L2 +2.546·BP1−P2 +2.546·BP1−P2 +BP1−C1 +2.546·BP1−P2
L3 0 +BP1−C1 +2.546·BP1−C1
L4 −BP1−P2 −BP1−P2 −BP1−P2 +BP1−C1
L5 −1.984·BP1−P2 −1.984·BP1−P2 +BP1−C1 −1.984·BP1−P2 +4.529·BP1−C1
L6 (MW) 0 −BP1−C1 −0.562·BP1−C1
f2 2 /(f2 1 − f2 2 ) = 1.546 f1 f2/(f 2 1 − f2 2 ) = 1.984
f2 1/(f 2 1 − f2 2) = 2.546 f1/(f1 − f2) = 4.529
f1/(f1 + f2) = 0.562
For the geometry-free (L4) linear combination, the BP1−P2 DCB (a synonym for τGD) plays
an important role, specifically with respect to the satellites observed as well as the receivers
involved. In case of GPS/GLONASS-combined receivers, two receiver-specific bias values
must be considered, one related to GPS and one related to GLONASS. From our experience,
GPS or GLONASS receiver bias values for BP1−P2 should not exceed the level of few tens
of nanoseconds. Corresponding estimates for all IGS stations processed at CODE may be
gathered from http://www.aiub.unibe.ch/ionosphere/ [Schaer, 1998].
The so-called Melbourne-Wübbena (MW, internally called L6) linear combination is essential
for ambiguity resolution (particularly on long baselines). Even when analyzing doubly
differenced data, the effect of BP1−C1 does not cancel out in case of a receiver network consisting
of more than one receiver class! In consideration of this fact, it is actually possible
to produce “ambiguity-fixed” BP1−C1 results. Such a refined DCB product is generated at
CODE (as part of the MW ambiguity resolution process).
13.2.1 When are DCBs Relevant?
Let us summarize standard applications where it is a must to take into account satellite
DCB information (according to Table 13.1):
• Positioning based on C/A code measurements only.
• Precise clock estimation (or time transfer) as soon as P1/X2 or C1/P2 receiver models
are involved.
• Ionosphere analysis relying on (raw or smoothed) GNSS code measurements.
• Ambiguity resolution using the Melbourne-Wübbena linear combination, if you have
baselines involving two different receiver models.
The necessary corrections due to DCBs are automatically computed and applied to the
observations in program GPSEST, provided that a DCB input filename is specified in panel
“GPSEST 1.1: Input Files 1”. Figure 13.4 illustrates the situation for ambiguity resolution when
relying on the pseudorange method (using the MW LC). The corresponding DCB input file
may contain information concerning BP1−P2 and/or BP1−C1 for GPS and/or GLONASS
(see also Figure 22.27).
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