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and validation input to the series of the NASA and USDA Soil Moisture Experi-
ments (SMEX) in the interests of hydrological science, technology and applica-
tions. In this aspect, the following problems are arising in the microwave
monitoring of soil moisture:
•
development of models parameterizing biometrical, soil properties and radio-
metric data for typical sites;
•
comparative evaluation of seasonal patterns in series of satellite, ground-truth
(and/or aerial) and laboratory data and simulations of soil-vegetation model;
•
conduct intercomparisons of radiation data and mean values of soil moisture
data at different depths with regard for the type of vegetation cover and amount
of biomass;
•
choice of constructive scheme for the data calibration basing on the available
radiative transfer model and results of measurements;
•
spectral radiometric data processing related to soil moisture and vegetation
cover parameters and results of modeling;
•
development of mathematical model for soil-vegetation system dynamics using
satellite,
field and laboratory data;
•
combining approach to parameterization of data needed for description of water
balance in soil-vegetation system and of data delivered from microwave satellite
(AMSR-E/Aqua, etc.) spacecraft observations, ground based microwave
observations, laboratory tests, in situ measurements (sampling) and mathemat-
ical modeling; and
•
using data of attenuation in vegetation and dielectric properties of soil and
vegetation samples as calibration and validation input to the GIMS.
2.5.2 Microwave Technology
The fundamental principles of soil moisture retrieval by means of the use of passive
microwave sensors and microwave radiometric technique for measuring soil
moisture properties have been established by Shutko (1986) and his disciples.
During a series of experiments, microwave radiometers were put on satellites,
aircraft, and ground-based vehicles. L-band passive microwave measurements were
the most informative in these experiments. Numerous investigations of sensitivity
of microwave measurements to vegetation biomass and soil moisture have shown
that remote sensing data give a possibility to solve important tasks from hydrology
and agriculture and to realize operational diagnostics of damage of stressful natural
processes. For instance, Ferrazzoli et al. (1992) carid out a comparative evaluation
of the potential of active and passive radiometers in estimating vegetation biomass
and soil moisture content. It was shown that low frequency data (L band) at a steep
incidence angle (10
cient and the
normalized temperature are correlated and sensitive to soil moisture content.
°
) con
rm that both the backscattering coef
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