A numerical study of backscattering from time-evolving sea surfaces: Comparison of hydrodynamic models

Results from a Monte Carlo simulation of backscattering from one-dimensiona l (1-D) time-evolving sea surface models are reported. A numerical electrom agnetic method based on an accelerated forward-backward approach is used to calculate backscattered returns from impedance surface profiles at inciden ce angles of 0 degrees (normal), 40 degrees, and 80 degrees. Surfaces are i nitialized as realizations of a Pierson-Moskowitz spectrum and then stepped in time through a numerical hydrodynamic method. Results from three distin ct hydrodynamic methods are compared: a linear evolution, the "improved lin ear representation" of Creamer et al. [7], and the "Watson-West" approach o f West et al. in [8]. Instabilities in the West model due to formation of s teep wave features limit the study to L-band backscattering for wind speeds less than 2 m/s, so that the surfaces considered are only slightly rough o n an electromagnetic scale. The small slope approximation for electromagnet ic scattering is shown to provide reasonable predictions in this limit. Sta tistics of the resulting surface profiles and backscattered fields are comp ared for the three models and are found to be similar in most respects. Bac kscattered field Doppler spectra, however, show differences, with the West model apparently capturing more nonlinear interactions in the surface evolu tion.