IEEE 9- Measurement of Soil Moisture Using Microwave Radiometer


The science of microwaves owes its origin to the
development of radar. Microwaves are part of
electromagnetic spectrum. This field became vitally
important as man reached out to space. Frequency range
of these waves are from 3 GHz to 30 GHz. Microwaves
have unique capabilities in remote sensing. The field of
microwaves remote sensing has come to a stage of rapid
growth. Microwaves can penetrate clouds and so the
sensors can operate in all weather conditions. They are
sensitive to the presence of moisture in the soil as well as in
vegetation or any another material which absorbs
moisture. Microwave sensors are of two types: active
sensors and passive sensors. Passive sensors have been
used for soil studies for the determination of moisture
content, oceanographic application to determine winds
over the ocean surface and water vapor content in
atmosphere as well as liquid water content in clouds. Soils
are composed of solids, liquids and gases mix in variable
proportions. Soil texture depends upon the size of the
particle and structure of soil depends on the way particles
are arranged. Soil has physical as well as electrical
properties. Colour, texture, grain soil etc. comprised the
physical properties where the electrical properties include
dielectric constant, conductivity and permeability.
Dielectric constant is the primary electrical property which
is used to estimate emissivity and brightness temperature
of soil. Emissivity is an important parameter for
microwave remote sensing, which provides information
about soils. All substances at a finite absolute temperature
radiate electromagnetic energy. Emissivity is the ratio of
energy emitted by object to black body maintained at same
physical temperature. Emissivity is a function of physical
and electrical parameters of the object and electrical
parameter of sensors.