Geoscience Reference
In-Depth Information
T
j
¼
j
T
e
ð
2
:
2
Þ
where
cient (or absorbing surface ability, or the blackness
level), T
e
is the effective surface temperature.
Expression (
2.2
) characterizes the thermal emission of the surface but does not
take into account the emission falling on the surface or re
κ
is the emission coef
fl
ected by it. The coef-
ective formula. The thermodynamic and
brightness temperatures are measured in Kelvins: T(K) = t(
cient
κ
is described by Frenel re
fl
C) + 273. The emis-
sivity is a function of dielectric permittivity of the object/surface of observation. For
a land surface, the dielectric permittivity is
°
first of all a function of soil moisture.
The higher a soil moisture content, the higher the permittivity of soil, the lower the
emissivity/intensity of radiation/brightness temperature of this piece of land.
For a water surface, the dielectric permittivity is
first of all a function of electric
conductivity of a water solution that is dependent on a concentration of salts, acids,
on a presence of oil
films and many other chemical substances. For example, the
higher salinity of water, the higher the dielectric permittivity of water solution, the
lower the emissivity/intensity of radiation/brightness temperature of this water
body. Within the 2
C, the radiation characteristics of
several surface types are shown in Table
2.13
. Table
2.14
shows the sensitivity of
radiation in the X-band (2
30 cm band, for t =10
30
°
-
-
30 cm) to the changes in free
water content in bare soil, soil density, salinity and temperature of the soil surface.
These data show that the main parameter affecting the intensity of a bare soil
radiation, practically independent of spectral band, is the soil moisture. Based on
this sensitivity it is feasible to estimate the value of soil moisture without a priori
data on the soil parameters.
The power registered by completely concerted receiver equals W=
3 cm) and L-band (18
-
-
κ
T
j
ʔ
f where
ʔ
f is the received emission branch. In the case when the model of soil with the
fl
at
Table 2.13 Basic microwave radiation characteristics of some typical surface types
Surface
T
j
(K)
ʺ
Metal
0
0
Water surface
90
-
110
0.3
-
0.4
Very wet soil
160
180
0.55
0.65
-
-
Very dry soil
250
270
0.85
0.93
-
-
Table 2.14 Sensitivity of a bare soil microwave radiation to variations in soil moisture (W), soil
density (D), salinity (S), and surface temperature (T)
Wavelength (cm)
ʔ
T
j
/
ʔ
W (K/g/cm
3
)
ʔ
T
j
/
ʔ
D (K/g/cm
3
)
Spectral band
ʔ
T
j
/
ʔ
S (K/ppt)
ʔ
T
j
/
ʔ
T (K/
°
C)
2
-
3
X
−
200
−
15
0.05
0.5
18
30
L
−
(200 to 300)
−
10
−
0.5
0.1
-
Search WWH ::
Custom Search