A simplified radiative transfer equation for application in ocean microwave remote sensing

Abstract

For inversion purposes in remote sensing applications, it is very useful to dispose of a simple, but nevertheless accurate enough, procedure for calculating brightness temperatures as received by spaceborne radiometers when observing the Earth surface through the atmosphere. Starting from an idea of Grody, a contracted form of the radiative transfer equation is proposed. It has the form of the equation for an attenuating atmosphere at constant temperature, above a lossy dielectric rough surface, under the specular approximation. However, it includes corrections for the atmospheric temperature profile and for the surface diffuse scattering. This last correction is an extension of that first proposed by Wentz. The resulting form of the equation and the importance of the correction terms are discussed for the practical case of the ocean surface. This equation has been used by the authors for the retrieval of geophysical parameters of the ocean surface and of the atmosphere from combined radiometric and radar measurements.

Microwave radiative transfer model validation

“…However, for the sake of simplicity the same value of ρ is applied to all channels here. Retrieved values for ρ generally lie in the range 1.0–1.2, which is consistent with the theoretical calculations of Guissard and Sobieski [1994] for a wind‐roughened sea surface at 50° incidence. It may be worth noting that an instrument that observed only in atmospheric windows would not be able to distinguish between a value of ρ > 1 and an increased atmospheric opacity due to clouds or the water vapor continuum.…”

A microwave satellite water vapour column retrieval for polar winter conditions

“…The brightness temperature T i measured at frequency ν i by channel i of a satellite-borne microwave instrument is parameterized by (Guissard and Sobieski, 1994)…”

Retrieval of temperature and moisture profiles from AMSU-A and AMSU-B measurements

“…Based on experience with NOAA-15 data, is computed for a path length (or opacity) equal to 1.15 times the path length for specular reflection (1.10 for channels [4][5][6][7][8][9][10][11][12][13][14]. This empirical adjustment accounts approximately for the effect of ocean surface nonspecularity, and is roughly consistent in magnitude with the calculations in [8]. For higher-emissivity land surfaces, the adjustment has a negligible effect.…”