Radiometric microwave field measurements of the complex dielectric constant of the water surface

Abstract

The paper describes the new remote method of radiometric in situ measurements of the real and imaginary parts of the dielectric constant (permittivity) of the underlying sea surface, which is an important parameter for remote sensing of the Earth. The method does not require absolute calibration of a radiometer, but uses the black body with the underlying surface temperature, which simplifies the measurement and allows one to measure the effective reflection coefficient at specified polarizations. It is shown that, for a fixed value of the reflection coefficient in sensing to the nadir, R(θ = 0°) = const, the reflection coefficient at the horizontal polarization is almost independent of the of dielectric loss angle. The reflection coefficient at the vertical polarization is most sensitive to the loss angle in the vicinity of the Brewster angle Rv(θ = θBr). The paper presents the results of measurements of the sea surface reflection coefficient using the radiometer operating at frequency of 37.5 GHz. The reflection coefficients at vertical and horizontal polarizations are calculated taking into account the antenna pattern and the distribution of slopes of a weakly roughened sea surface. The paper presents the example of determining the real and imaginary parts of the permittivity based on experimentally measured values of reflection coefficients at incidence angles close to the nadir and the reflection coefficient Rv(θ = θBr) at the Brewster angle. The obtained experimental values correspond to the theory within the limits of diversity of existing models.