Bernese GPS Software Version 5.0 - Bernese GNSS Software

6.5 Preprocessing Phase Observations
The change of the receiver clock (δk(t2) − δk(t1)) is computed using the linear combination
selected in option “Frequency for the solution” (usually the ionosphere-free combination L3)
for each epoch-difference.
Now, we check whether the no-cycle slip hypothesis b1 = b2 = 0 holds. The residual in L3
(ionosphere-free) linear combination is computed as
r3 = β1 r1 + β2 r2 , where β1 = f2 1
f 2 1 − f2 2
The following condition should be met:
|r3| ≤ 3g
and β2 = − f2 2
f 2 1 − f2 2
. (6.5)
(β1σ1) 2 + (β2σ2) 2 (6.6)
When screening baseline files the factor g = √ 8 = √ 2 3 is due to triple-differencing (two
receivers, two satellites, two epochs). When screening zero-difference files the factor is g =
√ 4 = √ 2 2 instead (one receiver, two satellites, two epochs).
Eqns. (6.3) resp. (6.4) allow us to compute the change of ionospheric refraction between the
epochs t1 and t2
I ij
kℓ (t2) − I ij
kℓ (t1)
independently for both carriers (we assume b1 = b2 = 0 at present). The mean value m is
computed as
m = 1
r1 +
2
f2 2
f2
r2
1
(6.7)
We check whether the condition
m ≤ Mion
(6.8)
is met. The value of Mion (option “Maximum ionospheric change from epoch to epoch”) and the
a priori RMS errors of the zero difference observables σ1 and σ2 (options “Sigma for L1/L2
observations”) are input parameters in panel “MAUPRP 8: Cycle Slip Detection/Correction”. If
conditions (6.6) and (6.8) hold, the no-cycle-slip hypothesis is accepted as true.
In the opposite case a search over the values b1 and b5 is performed. All combinations
r1
b1p = NINT
λ1
r1
b5q = NINT
λ1
+ p , p = −J1,...,−1,0,1,... ,J1
− r2
+ q , q = −J5,...,−1,0,1,... ,J5
λ2
(NINT = nearest integer) are formed and the “corrected” residuals
(6.9)
r1p = r1 − b1pλ1 , r2pq = r2 − (b1p − b5q)λ2 (6.10)
are tested in the same way as the original residuals r1 and r2. The user has to specify
the search ranges J1 and J5 (see “Search width to find L1/L5 cycle slip correction” in panel
“MAUPRP 8: Cycle Slip Detection/Correction”). If one combination of r1p, r2pq meets the nocycle-slip
hypothesis, this pair is assumed to be the cycle slip correction.
If no combination for r1p, r2pq is found meeting the no-cycle-slip hypothesis a new ambiguity
parameter should be introduced. But introducing too many ambiguity parameters would
Bernese GPS Software Version 5.0 Page 119