Geoscience Reference
In-Depth Information
8.6 Vegetation Media as the Object Under Study
of Attenuation of Electromagnetic Waves
Many investigators (Basharinov et al. 1979; Hansen et al. 2002; Zhan et al. 2002;
Burkov and Krapivin 2009; Chukhlantsev 2006) support a constructive technology
for microwave monitoring of vegetation covers. However, greater accuracy of this
technology is required because various vegetation covers, especially vegetation
canopies, are very dynamic and complicated for experimental study or model
parameterization. In this respect, there are two aspects. One is connected with the
creation of a highly productive technology to estimate the land cover characteris-
tics. The other is connected with the climate change problem through the green-
house effect (Kondratyev et al. 2003c). In these cases the GIMS-technology
recommends a balanced scheme for the solution of problems of land cover moni-
toring. As follows from Armand et al. (1997), a combination of experimental and
theoretical studies of attenuation of microwave radiation by vegetation cover is
required. It is actually possible to synthesize the experimental dependence between
attenuation and a restricted set of vegetation parameters. An estimation of attenu-
ation of microwave radiation by vegetation cover in real time is possible only with
the application of microwave models and interpolation algorithms.
From the point of view of microwave remote sensing, the knowledge of the
water content of vegetation is an important element which has to be used for the
synthesis of a model of attenuation of microwave radiation by the vegetation. This
knowledge can be acquired by making use of the fact that water absorption features
dominate the spectral re
ectance of vegetation in the near-infrared spectrum (Sims
and Gamon 2003). Using such indexes as the normalized difference vegetation
index (NDVI), plant water index (PWI), the leaf area index (LAI), the simple ratio
vegetation index (SRVI), and the canopy structure index (CSI) it is possible to
determine the canopy structure and photosynthetic tissue morphologies. The cor-
relation between the leaf water content and the leaf-level re
fl
ectance in the near-
infrared has been successfully studied by many authors that linked the leaf and
canopy models to study the effects of leaf structure, dry matter content, LAI, and
canopy geometry. As a result, it is possible to parameterize the forest structure
including the canopy and crown closure, stem density, tree height, crown size, and
other forest parameters (Tables
8.13
and
8.14
).
fl
Table 8.13 Some estimations of parameters for different types of branches (Karam et al. 1992)
Branch
group
Diameter range
(cm)
Average diameter
(cm)
Average length
(cm)
Number density
(m
−
3
)
1/stems
0.0
-
0.40
0.10
18
250.00
2
0.5
1.90
1.28
14
11.40
-
3
2.0
2.90
2.60
32
0.43
-
4
3.0
-
6.90
5.00
58
0.33
5/trunk
7.0
17.1
9.00
76
0.14
-
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