Geoscience Reference
In-Depth Information
Table 8.14 Dielectric
constant values (Karam et al.
1992)
SPF element
Frequency band
L
X
Leaves
19.58
−
j5.54
14.9
−
j4.9
Branch/stems
27.30
−
j8.4
20.0
−
j9.7
Soil
5.00
−
j0.7
5.0
−
j0.4
Quantitative information about SPF properties may be obtained by means of
different remote sensing techniques based on passive microwave data. This
approach is particularly effective under an estimate of the hydraulic parameters of
the soil-plant formations. The knowledge of these parameters allows the water
balance of a territory occupied by vegetation of a given type to be parameterized
and plant to be modeled. Under this approach a comparison of remote data regis-
tered at different EMW ranges may provide a high precision of estimates of the
water content in the various layers of the SPF (canopy, trunks, stalks, and soil).
Moreover, the combination of data analysis with remote sensing allows one to
estimate the parameters of the ground vegetation cover and its role in the
fl
fluxes of
sensible and latent heat from the surface to the atmosphere.
A problem of wavelength choice and the combination of its ranges with classes
of solved tasks is now within the sight of many investigators. The theoretical
foundation of this choice lies in the area of thermal radiation transmission theory.
Speci
cally, for the monochromatic case the transmission equation has:
dI
ðÞ=
dz ¼ J
ðÞa
I
ðÞ
ð
8
:
10
Þ
where
cient, J(z) is the emission source distributed by the
coordinate z, and I(z) is emission intensity at point z. Under these conditions, the
following equation is valid for an unscattering atmosphere: J(z)=
ʱ
is the absorption coef
ʵ
1
(z)B(z), where
ʵ
1
is atmospheric emissivity,
exp hf
=
k
ðÞ
1
B
ðÞ
¼ 2hf
3
=
c
2
½
f
g
1
;
c is frequency. It is known that hf < kT
in microwave range and Rayleigh-Jeans approximation B(z)=2kT/
h, c, and k are fundamental constants, f =
ʽ
2
is valid. Here
ʻ
10
−
23
JK
−
1
×
ʻ
k = 1.38
is the Boltzmann constant,
is the wavelength.
Equation (
8.10
) can be solved by
Z
1
T
j
¼
j
T
e
sð
0
;1Þ þ
T
ð
u
Þ
Q
ð
u
Þ
du
;
ð
8
:
11
Þ
0
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