INVESTIGATION OF DOPPLER PROPERTIES OF S-BAND IN-PLANE BISTATIC SEA ECHOES THROUGH NUMERICAL MONTE CARLO SIMULATIONS: EXACT SOLUTION, TWO-SCALE MODEL, AND SMALL SLOPE APPROXIMATION

Doppler characteristics are intrinsic to scattering from ocean surface and can be used for sea state retrievals. In this study, bistatic reflections of time-harmonic S-band signal from evolving sea-like surface are simulated in 2-D space using an exact technique based on the first-principles boundary integral equation formulation. Large Monte Carlo ensembles allow obtaining well-averaged Doppler spectra. The behavior of basic spectral parameters (mean shift and width) at both VV and HH polarizations is analyzed across a broad range of scattering angles (the incident angle is kept at 45 degrees). Changes in those parameters with the sea state (wind speed) are examined. The simulations are also repeated with the two approximate scattering models: the coherent Two-Scale Model and the second-order Small Slope Approximation, providing rigorous assessment of their ability to predict Doppler properties of sea surface scatter.