Geoscience Reference
In-Depth Information
The approximate ranges of radar return changes are as follows: 6
8 db for whole
-
range of soil moisture changes; 10
18 db for whole possible scale of roughness
-
changes; 8
10 db for vegetation characteristics changes; 6
8 db for changes in angle
-
-
of observation, 30
off nadir. Now, let the changes in radar returns caused
by soil moisture changes be referred to as signal, and the changes in radar returns
caused by the changes in other than moisture parameters referred to as noise. Then,
the signal-to-noise (s/n) ratio calculations will result
°
<
ʘ
<60
°
in a s/n = 0.33
0.8 for
-
roughness, a s/n = 0.6
1.33 for changes in angle.
Similarly, calculations of the signal-to-noise ratio for the naturally emitting
radiation are higher: s/n = 2
1.0 for vegetation, and a s/n = 0.75
-
-
5 for roughness, s/n = 1
3 for vegetation, s/n = 2
3 for
-
-
-
changes in angle. This shows the bene
ts of using passive systems, in spite of a more
coarse spatial resolution and a smaller swath, in combination with active systems.
Microwave remote sensing equipment was partly described in Chap. 2 . An
experimental usage of this equipment for solving agricultural tasks has shown high
effectiveness and decreasing risks related with well-timed evaluation of basic char-
acteristics of agricultural soils including soil salinity and its humidity, as well as the
crop maturity. Figure 9.30 compares the different penetrative ability of L-, P-, and
VHF-band radars to see a ground surface through vegetation cover. In L-wavelength
band, the signal is mainly dependent on canopy characteristics. The P- band returns
are much less affected by grass vegetation and a back-scattered. It clearly indicates the
effect of a soil and water surface along with some effect of vegetation. The VHF-band
image clearly demonstrates no effect of canopy on signal returns for grass and bushes.
More detailed consideration of the raised problems are given in Chap. 2 .
Comparison is given in Fig. 9.28 of a different penetrative ability of L-, P-, and
VHF-band radars to
a ground surface through vegetation cover. In L-wave-
length band, the signal is mainly dependent on canopy characteristics. The P- band
returns are much less affected by grass vegetation and a back-scattered signal
clearly indicates the effect of a soil and water surface along with some effect of
see
Fig. 9.30 Images obtained by the improved SAR System IMARC, Spas-Klepiki, Ryazanskaya
Region (Gulyaev et al. 2005)
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