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For active remote sensing of soil moisture, the angle of incidence and the angle of
observation (reflection) are very important parameters. Various percentages of soil-water mixture
give rise to large contrast in dielectric constant of the soil, which produces large variations in
the microwave reflection and transmission coefficients (Vyas, 1982; Topp et al., 1985; Ghosh et al., 1998; Calla et al., 2003; and Puri et al., 2004). Knowledge of viewing
angle-dependent sensitivity of the antenna will be of immense use for microwave remote sensed data.
Lab- based soil studies are very important for calibration purposes. The spectral reflectance
data might enable the determination of the frequencies most useful for discriminating type,
texture and moisture content of the soil. Since the dielectric constant of water is ~ 80 at
microwave frequencies, variations in moisture content make significant change in the dielectric
constant of the soil, leading to changes in the output.
Free space microwave measurement is a nondestructive and contactless
method (Kraszeweski et al., 1997; and Slima et al., 1999). Studies on soil using the entire 8-18
GHz frequency range are very sparse. In this paper, a free space reflection method, using X and
Ku bands standard gain horn antenna to measure the viewing angle-dependent reflectance
due to wet soil, is reported. Two types of black soils were investigated. Black1 (BLK1) from
sugarcane field and Black2 (BLK2) from the field in which crops do not grow at present (dead
soil). BLK1 was made up of coarse sand with some clay, whereas BLK2 was gravelly with more
clay. All these soils were taken from Kolhapur district in Maharashtra state, India. Reports
are available on the properties of various types of soil like sandy, loamy, etc. In this work,
same type of soil was studied (both black). The aim behind the investigation was to see the
feasibility to distinguish the quality and type of the soils from viewing angle-dependent
(reflection) microwave observations. |
