Global Positioning System Reference
In-Depth Information
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[24
Lin
—
3.7
——
Lon
*PgE
Figure 7.12
Variation in extra widelaning.
Figure 7.12 shows the variation of the computed L1 double-difference ambigu-
ity
using (7.39). For this 1-hour stretch of data the elevation angles of both satellites
we
re above 45°. The integer double-difference wide-lane ambiguities were estimated
fir
st using (7.33) and then substituted in (7.39). The variation around the integer
−
[24
42 is due to double differenced multipath. The ionospheric effects cancel because
th
e baseline is so short. Studying figures like Figures 7.11 and 7.12 it can be read-
ily
appreciated that, under favorable circumstances, the L1 double-difference inte-
ge
r ambiguities can be determined from just one epoch of observations using the
ge
ometry-free solution.
We substitute the geometry-free epoch equation (7.19) into the ionospheric-free
eq
uations (6.91) and (6.94) and ionospheric equations (6.97) and (6.98). For single
an
d double differences we obtain
P
km,
IF
P
km,I
Φ
β
f
P
km,
1
− γ
f
P
km,
2
P
km,
1
−
P
km,
2
≡
=
p
km,
IF
Φ
p
km,
1
p
km,
2
β
f
Φ
− γ
f
Φ
p
km,I
p
km,
1
p
km,
2
Φ
− Φ
(7.40)
p
km
T
km
p
km,
IF
,P
δ
1
0
0
0
δ
ρ
−
d
t
km
+
I
km,
1
,P
N
km,
1
N
km,
2
p
km,I,P
01
− α
f
0
0
+
1
0
β
f
λ
1
−γ
f
λ
2
p
km,
IF
,
Φ
δ
δ
01
− α
f
λ
1
−λ
2
p
km,I,
Φ
