POLARIMETRIC PASSIVE REMOTE-SENSING OF OCEAN WIND VECTORS

This paper investigates the theory of polarimetric passive remote sens ing of wind-generated sea surfaces and the potential application of po larimetric radiometry to ocean wind remote sensing. Theoretical polari metric emission coefficients of small-scale sea surfaces are evaluated using the small perturbation method (SPM). The SPM is derived to seco nd order and applied to the Stokes vectors of thermal emission from ra ndom rough dielectric surfaces described by anisotropic directional sp ectra. To verify the accuracy of the SPM, a Monte Carlo simulation is performed to calculate the Stokes vectors of the emission from the sim ulated one-dimensional random rough surfaces with a power law spectrum for various observation angles and surface parameters. The theoretica l results of the SPM for all four Stokes parameters are in excellent a greement with the numerical results obtained from the Monte Carlo simu lation. Moreover, the second-order coherent fields are indispensable i n the theoretical evaluation of the third and fourth Stokes parameters . Otherwise, the reflectivities of random rough surfaces would be sign ificantly overestimated, and the sips of the third and fourth Stokes p arameters would be incorrect. The SPM is then applied to small-scale s ea surfaces described by an empirical sea surface spectrum. It is foun d that the azimuthal signatures of Stokes parameters agree qualitative ly well with aircraft Ku-band radiometer data. Theoretical model funct ions of the Stokes parameters are illustrated. Advantages of wind dire ction retrieval using polarimetric Q and U measurements are discussed, and it is expected that a spaceborne polarimetric radiometer has a po tential of providing wind vector measurements with uniform accuracy ac ross all parts of swath.