Bernese GPS Software Version 5.0 - Bernese GNSS Software

6. Data Preprocessing
This epoch-difference solution is not as accurate as the result of the least-squares adjustment
in the final parameter estimation program GPSEST (using either zero-differences for stations
or double-differences for baselines), but it is a fair approximation of the final solution. The
main advantage has to be seen in the fact that an undetected cycle slip corrupts one epochdifference
only (and not all zero-differences or double-differences after the slip). Therefore,
this solution may be used as reference for the automatic cycle slip detection in the next
step.
The epoch-difference residuals are computed and stored in a scratch file (the residuals are
computed for all observations not only for those identified as “clean” in the first step).
6.5.3 Automatic Cycle Slip Detection
The algorithms described in the following are specific to GPS. Modifications for GLONASS
are described in [Habrich, 1999].
First, the program corrects big jumps on the single-difference level when screening baseline
files. Such jumps usually originate from the receiver clock and are common to all satellites.
Therefore, these clock jumps are only relevant for the receiver clock synchronization
for double difference processing algorithms. This step is skipped if zero-difference files are
preprocessed because in this case receiver clock corrections may be estimated later in the
parameter estimation program GPSEST.
Then, the results of the previous two steps are used to detect the cycle slips in the following
way: The epoch-difference residuals stemming from the second step (they have been stored
in an auxiliary file – see Section 6.5.2) are inspected. We assume that we have observations
in two carriers L1 and L2 and write
r1 the epoch-difference L1–residuum (we do not explicitly indicate the one or two receivers,
two satellites, and two epochs pertaining to this epoch-difference) and
r2 the epoch-difference L2–residuum.
The user may select either the COMBINED or BOTH method in option “Screening mode,
frequency to check” of input panel “MAUPRP 3: General Options” (see the corresponding help
panel).
Cycle Slip Detection: Dual Band Algorithm
If the COMBINED method is used, MAUPRP interprets the residuals as follows:
r1 = b1λ1 + I ij
kℓ (t2) − I ij
kℓ (t1)
I ij
kℓ (t2) − I ij
kℓ (t1)
, r2 = b2λ2 + f2 1
f 2 2
(6.3)
where I ij
kℓ (t) is the ionospheric refraction “as seen” by the L1 carrier at time t (see
Eqns. (2.37)). If zero-difference files are preprocessed the change of the receiver clock must
be considered in addition:
r1 = b1λ1 +
I ij
k (t2) − I ij
r2 = b2λ2 + f2 1
f 2 2
k (t1)
+ δk(t2) − δk(t1) ,
I ij
k (t2) − I ij
k (t1)
+ δk(t2) − δk(t1)
(6.4)
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