Polarimetric Passive Remote Sensing of Ocean Surface

Abstract

Abstract : In the microwave remote sensing of ocean surface, the use of polarimetric passive techniques has shown potential for enhancing the retrieval of wind speed and directions. Recent theoretical and experimental research activities have concentrated on studies of polarimetric thermal emissions regarding the anisotropic ocean surface assuming a smoothly varying surface profile. However, under high wind conditions, the presence of breaking water waves, foam patches and bubbles will affect the polarimetric brightness temperatures of the plain ocean surface. The significance of foam on the ocean surface was recognized a long time ago, and several subsequent experiments performed have verified its importance. Previous studies of the foam contribution to the emissivity of ocean surface were based on empirical formulations derived from experimental data. Although several attempts at theoretically modeling the foam have been presented, it is difficult to incorporate them with rough ocean surface. The more realistic modeling for foam-covered ocean surface has been proposed by Huang et al., who consider the sea foam to be a layer with water particles over a rough sea surface. However, it is not suited to model the sea foam as the layer of spherical water particles, since the sea foam is dominated by water bubbles. In this chapter, we present the theoretical study on the polarimetric thermal emissions from foam-covered ocean surface based on a composite volume and rough surface scattering model using the radiative transfer theory. We model the locally foam-covered ocean surface as a random layer with water bubbles. The small perturbation method (SPM) is used for random rough ocean surface, where the bistatic scattering is calculated up to the second order. The radiative transfer equations for foam layer are solved using an iterative technique. The model predictions are compared with measurement data.