Digital Signal Processing Reference
In-Depth Information
Fig. 7.3
Occultation
geometry with straight line
This method needs high precision orbit determination data and its processing
procedure is complex. Usually, it will be used for atmosphere inversion and
planetary radio occultation.
7.2.2
Ionosphere Inversion Based on TEC
Ionosphere inversion using TEC data is based on the fact that the bending angle due
to the ionospheric refraction is very small (Hajj and Romans
1998
), especially for
upper ionosphere. Together another assumption of spherical symmetry in GNSS-
RO inversion, the signal path from GNSS transmitter to the LEO satellite can be
modeled as a straight line shown in Fig.
7.3
.
The first step of ionosphere inversion based on TEC is to compute the slant
total electron content along the signal path with GNSS dual-frequencies or single
frequency data. TEC can be estimated by Eq. (
7.13
) with GNSS dual frequencies
data, i.e.,
f
1
2
f
2
2
40:28 .f
1
2
TEC
D
f
2
2
/
.L
1
L
2
.N
1
1
N
2
2
C
b
1
b
2
//
C
"
L
f
1
2
f
2
2
40:28 .f
2
2
D
f
1
2
/
.P
1
P
2
.B
1
B
2
//
C
"
P
;
(7.13)
where
L
1
,
L
2
,
P
1
and
P
2
are GNSS carrier phase and pseudorange observables,
respectively,
N
1
,
N
2
,
1
and
2
are ambiguities and wavelengths for
L
1
,
L
2
,
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