Geoscience Reference
In-Depth Information
where
Z
b
a
;
b Þ ¼ exp ½
z Þ dz
a
uence of various
atmospheric layers on the receiving signal. Formula ( 8.11 ) converts expression
T j =
The weight function Q(u)=
∂˄
(u,
)/
u describes the in
fl
c values are given in Table 8.15 .
Thus, a set of vegetation-related parameters should be generated using speci
ʺ
T e into a whole. Examples of speci
c
time and space resolutions as the basis for the calculation of EMW attenuation by
the vegetation layer. Available remote monitoring data should be used as input
information for algorithms and models to synthesize the spatial-temporal distribu-
tion of the attenuation effects. In this context, the most important parameter is the
dielectric constant. Some estimations of this characteristic are given in Table 8.14 .
For example, for the stem dielectric constant a representative value at the L band is
found to be 27.3
j8.4. The leaf dielectric value varies from 8.77
j2.88 to
19.58
j5.54. An average value of
the leaf dielectric constant equals to
19.58
j5.54. The values of the dielectric constant at X band equals to 14.9
j4.9
and 20.0 j9.7 for leaves and branches, respectively.
Detail and complete study of the EMW attenuation by the vegetation layer was
realized in the framework of the ISTC Project #2059
Screening Effect of Vege-
tation in Active (SAR) and Passive (Radiometric) Remote Sensing of the Earth
s
Covers and in Radio-Communication in UHF-, VHF-, and Microwave (X-, C-, S-,
L-, and P-) bands
'
(Chukhlantsev 2006). The goals of this Project were the
following:
acquiring systematized data about electromagnetic waves attenuation by dif-
ferent types of vegetation covers, mainly in the meter wavelength band, but also
in decimeter and centimeter wavelength bands (UHF, VHF, P-, L-, S-, C-, and
X-bands) using theoretical and experimental investigations.
￿
developing advanced, more sophisticated, and generalized models, compared
with the existing SAR and microwave radiometric models of different types of
￿
Table 8.15 Brightness
temperatures typical of some
land covers
Land cover
ʻ
= 0.8 cm
ʻ
= 1.35 cm
T Tj,min
T j,max
T Tj,min
T j,max
Desert
251
261
245
270
Cuntivated steppe
255
268
257
277
Steppe covered
by snow
246
261
241
260
Ice covered by snow
247
263
231
253
Ice
239
247
235
254
Sea surface
136
171
110
168
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