Global Positioning System Reference
In-Depth Information
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Equation (7.33) is frequently used to screen the observation for cycle slips. Alter-
natively, one might attempt to determine the wide-lane integer from a short set of
observations, conceivably just one epoch, and then constrain that integer to resolve
the integer for
N
1
rapidly. As more frequencies are added to the satellites one will be
able to carry out additional widelaning (Hatch et al., 2000).
Figure 7.11 shows the computed wide-lane ambiguity (7.33) for three consecutive
days. The elevation angle of satellite PRN 07 changes from 50° to 5° during the
1.5 hours of observations. The plotted lines are shifted by integers for purpose of
graphical separation. It can be readily seen that the wide-lane integer ambiguities can
be estimated from these data. The origins of the plots are shifted 4 minutes each day in
order to emphasize similarity in multipath disturbances. The same receiver-satellite
geometry repeats about 4 minutes earlier each succeeding day.
The geometry-free epoch solution also applies to relative positioning. Using sub-
scripts
k
and
m
, and the superscripts
p
and
q
to indicate differencing, we obtain from
(7.19)
[24
P
km,
1
P
km,
2
Φ
p
km,
1
,P
ε
km,
1
,P
ε
km,
2
,P
ε
km,
1
,
Φ
ε
km,
2
,
Φ
p
km
−
T
km
Lin
—
2.9
——
No
*PgE
ρ
d
t
km
+
δ
11 00
1
I
km,
1
,P
N
km,
1
N
km,
2
p
km,
2
,P
α
00
δ
f
=
+
+
p
km,
1
p
km,
1
,
1
−
1
λ
1
0
δ
Φ
p
km,
2
1
−α
f
0
λ
2
p
km,
2
,
Φ
δ
Φ
(7.36)
[24
Figure 7.11
Variation in wide-lane ambiguity.
