Geoscience Reference
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land surfaces but also about deep characteristics depends on the choice of electro-
magnetic range. In the infrared range, total emission is formed into very thin surface
layer. Electromagnetic waves of microwave range are absorbed powerfully by the
land and water surfaces. The depth of its spread into the water environment is
measured in hundredth of millimetre; whereas dry soils, continental ices, and dry
snow this value can reach several tens of wavelengths. It allows to realize the remote
investigations of soil, ice and snow covers up to considerable depths.
Penetrating ability of radio-waves gives the advantage particularly under the
sensing of land covers. Vegetation without a dense canopy (grass, cereals, etc.)
absorbs radio waves weakly and this is the reason radio-observation of soil covers
through this vegetation is possible. Radio-waves can spread across the soil up to the
depth reaching one metre.
Main defect of microwave radiometric observations consists in the comparative
low spatial resolution in comparison with the optical range. In the radio-range the
high spatial resolution is achieved by the multichannel application and speci
c data
processing methods. It demands large economic investments.
Let us consider some aspects of active location. Let us supposed that irradiation
at the nadir of a smooth plot is realized. In this case the signal power re
fl
ected from
ʺ
0
|
2
(16
H
2
)
−
1
, where p is the emitted power, G is
ˀ
the land surface equals W = pGA|
the coef
cient antenna area, H is the
antenna height above the ground surface,
ʺ
0
is the surface reflection coefficient. If
all instrumental parameters and antenna height are known the ratio of power
accepted to that of the one received determines the value of the re
cient of directed action of antenna, A is the ef
fl
ection coef
-
cient. In the case when the soil is uniform by depth the re
fl
ection coef
cient equals
1/2
1/2
+ 1), where
ʺ
0
=(
ʵ
−
1)/(
ʵ
ʵ
is the dielectric ground permittivity. For the
estimation of
ʵ
the following approximate formula exists
2
1
=
2
1
=
2
s
e
¼
e
w
p
w
þ e
½1
p
w
;
ð
2
:
1
Þ
where
ʵ
w
is the dielectric water permittivity, p
w
is the relative volume concentration
of free moisture in the soil,
ˁ
s
)
2
ʵ
s
≈
(1 + 0.5
is the dielectric permittivity of dry
2gcm
−
3
).
ground, and
ˁ
s
is the dry ground density (1
-
From Eq. (
2.1
) it
is seen that re
fl
ected signal power give a possibility to
determine the re
fl
ection coef
cient and, consequently, dielectric ground perme-
ability. The value of
ʵ
de
nes the ground density when it is dry or the water content
if it is wet.
Dielectric properties of land covers are basic to use the radiometric methods for
its diagnosis under different situations. Speci
cally, the knowledge of spectral
coef
cient for the emission in the millimetre range allows to estimate the properties
of snow or ice layer.
The re
cient is determined as well as by passive methods using the
measurements of radiothermal emission intensity. The intensity of background
radiation at microwave range according to the Kirhgof law is characterized by the
brightness temperature
fl
ection coef
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