Geoscience Reference
In-Depth Information
where BT is the brightness temperature at frequency
f
for the polarized component
p. When there is little vegetation cover over the land surface, the value of
τ
can be
de
ned as zero. So the MPGR of bare ground can be written as Eq. (
7a
) for
polarization and Eq. (
7b
) for gradient ratio.
PR
f
¼
e
f
V
e
f
H
= e
f
V
þ e
f
H
ð
7a
Þ
¼
e
f
1p
e
f
2p
= e
f
1p
þ e
f
2p
GR
f
1p
f
2p
ð
7b
Þ
According to Paloscia and Pampaloni [
13
], we can assume
ʵ
soil
(
ʵ
V
+
ʵ
H
)/2, and
T
c
=T
soil
. Then Eq. (
7a
,
7b
) can be further simpli
ed as
s=
l
MPGR
s; ðÞ
MPGR 0
; ðÞ
e
ð
8
Þ
Since microwave radiation is polarized, it can be used to depict the condition of
vegetation if the vegetation-soil is made a pattern. Equation (
8
) shows that MPGR
mainly depends on
µ
τ
, and MPGR values fall as vegetation becomes thicker.
Therefore, MPGR indicates the density of land surface vegetation cover. Vegetation
cover also greatly in
and
uences the land surface temperature. Thus, we classify the
land surface vegetation cover conditions into several types based on values of
MPGR (Fig.
1
).
fl
4 Result and Discussion
To identify the behavior of each land cover class, we
first selected/determined
sample sites in all 17 land cover classes through the use of the ArcGIS system. Then
their maximum, minimum, mean, and standard deviation were derived all horizontal
and vertical AMSR-E frequencies to determine which combination of MPGR are
best suited for land cover classi
find (Fig.
2
) that vertical and higher
frequency are closer to actual physical land surface condition/type compared with
horizontal and lower frequency. Low frequencies of AMSR-E are hardly in
cation. We
uenced
by atmospheric effects during bad weather, but they are affected by surrounding
(near features) and background surface effects since they absorb less and scatter
more by soil. Frequencies of 89 GHz and above are more likely to be in
fl
uenced by
the atmosphere than other AMSR-E bands, especially during bad weather conditions
[
16
,
17
]. Our approach makes use of the 89 GHz channels, because the 89 GHz data
are in
fl
uenced less by surface effects than the lower frequencies, and the 89 GHz
channels have successfully been used in water and sea ice concentration retrievals
under clear atmospheric conditions [
18
]. Lower frequencies help to distinguish the
land surfaces
'
vegetation cover conditions. However, the BT differences between
fl
Search WWH ::
Custom Search