Bernese GPS Software Version 5.0 - Bernese GNSS Software

13. Differential Code Biases
Figure 13.3: P1–C1 code bias estimates for the GPS satellite constellation, as computed
at CODE.
13.2 How to Correct P1–P2 and P1–C1 Code Biases
By convention, IGS precise satellite clock corrections have to be consistent to the P1 and
P2 observables. This implies that each clock correction contains the ionosphere-free linear
combination of (unknown) BP1 and BP2 biases, i.e., 2.55 · BP1 − 1.55 · BP2. The same is by
the way also true with regard to GPS broadcast satellite clock information.
It is obvious that code tracking data from both the C1/X2 and the C1/P2 receiver class must
be corrected in order to achieve full consistency with P1/P2 data, or precise satellite clock
information. On the basis of BP1−P2 and BP1−C1 DCB values for the GPS/GLONASS
satellite constellation, corrections may be derived for the three receiver classes initially
introduced.
Table 13.1 summarizes the necessary DCB corrections for six different linear combinations
derived from the available code observables. As expected, no DCB correction is needed for
the ionosphere-free (L3) linear combination of P1/P2 code data. To correct the (commonly
used) L3 linear combination of C1/X2, or C1/P2, just a correction specific to the BP1−C1
(not BP1−P2) DCB is necessary.
Table 13.1 includes also the “classical” single-frequency (C1) case (see L1 for C1/X2 or
C1/P2). An interesting detail is that the DCB correction in that case is not only −τGD =
+1.55·BP1−P2 as suggested by [GPS-ICD, 1993] (cf. Eqn. (13.1)) but it includes in addition
a correction term responding to +BP1−C1.
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