Computation of the vertical and horizontal polarizations of brightness temperature of flat surface water over the Persian Gulf at the L-Band

Abstract

The brightness temperature is the principle parameter detected by passive microwave radiometers. The radio frequency interference at L-band radiometers (e.g., SMOS, Aquarius and SMAP) impacts the quality of brightness temperature detection in many parts of the world such as the Middle East and the Persian Gulf. In the present work, vertical and horizontal polarizations of brightness temperature over flat surface water of Persian Gulf at L-band were calculated by using physical computations and an empirical model. For this purpose, Rayleigh–Jeans radiation law and Fresnel reflection equations were used and complex permittivity was calculated by Blanch and Aguasca model. Input data for the model calculations are temperature and salinity that were provided from World Ocean Atlas 2013. The calculations showed that the brightness temperature distribution in the Persian Gulf experiences significant spatial and seasonal variations. At nadir incidence angle, the vertical and horizontal components of brightness temperature over the Persian Gulf vary in the range 90.5–96.5 °k and 85.5–90.2 °k, respectively. At off-nadir incidence angle, the temporal variability pattern of brightness temperature horizontal polarization is similar to its vertical counterpart but the difference between them significantly increases.