Digital Signal Processing Reference
In-Depth Information
The dielectric constant varies between different types of reflecting surfaces.
Scientific and engineering literature compiles the values measured at the L-band
of the spectra for some types of interfaces. For example,
Ulaby et al.
(
1982
)gives
the relative dielectric constant of the saline water as:
D
r
C
i
i
(8.12)
.
s
w
0
s
w
1
/
1
C
.2f
s
w
/
2
D
s
w
r
1
C
(8.13)
2f
s
w
.
s
w
0
s
w
1
S
i
e
2
0
f
/
i
D
C
(8.14)
1
C
.2f
s
w
/
2
where f is the frequency,
s
w
1
D
4:9, and:
D
.25
T /.2:033
2
C
1:266
4
.25
T/
C
2:464
6
.25
T/
2
S.1:849
5
2:551
7
.25
T/
C
2:551
8
.25
T/
2
//
(8.15)
D
S.0:18252
1:4619
3
S
C
2:093
5
S
2
1:282
7
S
3
/
S
i
(8.16)
where T is the temperature of the water in degrees Celsius and S the salinity in parts
per thousand. And,
s
w
0
D
.87:174
1:949
1
T
1:279
2
T
2
C
2:491
4
T
3
/A
(8.17)
A
D
1
C
1:613
5
TS
3:656
3
S
C
3:21
5S
2
4:232
7
S
3
(8.18)
s
w
0
s
w
D
2
B
(8.19)
D
1
C
2:282
5
TS
7:638
4
S
7:760
6
S
2
C
1:105
8
S
3
B
(8.20)
s
w
0
D
1:1109
10
3:824
12
T
C
6:938
14
T
2
5:096
16
T
3
(8.21)
Recent studies, in support to the L-band radiometric missions (SMOS, Aquarius),
have refined this model. See for example
Blanch and Aguasca
(
2004
).
Typical values for soil permittivity at L-band can be found in (e.g.
Ulaby et al.
1986
), and listed in Table
8.2
.
Figure
8.13
compiles the reflectivity of several Earth surface types for co-polar
and cross-polar circular polarized signals, at GNSS frequency bands. It is clear that
at nadir and small incidence angles, the reflection process is essentially cross-polar,
meaning that most of the incident, RHCP, signals swap to LHCP after reflection. At
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