Variation of Dielectric Constant, Emissivity and Scattering Coefficient of Coastal Saline Soils of Maharashtra Region at Various Microwave Frequency Bands

Abstract

This study presents experimental measurements of the complex dielectric constant of five coastal saline soil samples collected from representative locations along the Maharashtra coast — Pen, Alibag, Murud, Tarkarli, and Dapoli — at microwave frequency bands spanning 2 to 10 GHz, covering the L, S, C, J and X bands. A standard microwave bench setup operating in TE10 waveguide mode with VSWR detection was used. The measured complex dielectric constants were used to estimate emissivity via the Fresnel emissivity model and backscattering coefficients via the small perturbation model (SPM). The real part of the dielectric constant (ε′) was found to decrease with increasing frequency for all five samples. The decrease in ε′ from 2.35 GHz to 9.685 GHz for all five samples, consistent with the Debye dipolar relaxation model. At constant moisture condition, emissivity for vertical polarisation increases with incidence angle up to a pseudo-Brewster angle — ranging from approximately 54° (X-band) to 71° (L-band) — and then decreases sharply; for horizontal polarisation, emissivity decreases monotonically. Backscattering coefficient for vertical polarisation increases up to approximately 60°–70° and then decreases, while horizontal polarisation values remain stable up to 40° 50° before decreasing. These results are useful for designing passive and active microwave remote sensors for coastal saline soil monitoring in Maharashtra.