Spectral properties of radar return from the ocean surface according to a Bragg-based composite surface model

Doppler spectra of the radar return from the ocean surface include information on the line-of-sight velocity of the scatterers and can thus be evaluated for direct measurements of surface currents and the orbital motions of long waves. However, experimental results obtained from along-track interferometric SAR (ATI) and Doppler scatterometry indicate that measured Doppler spectra can significantly deviate from first-order model predictions. The author presents an improved composite surface model for the computation of Doppler spectra which is based on Bragg scattering theory and includes contributions associated with the complete two-dimensional ocean wave spectrum. In addition to geometric effects, the asymmetric distribution of short ripple waves along longer waves due to hydrodynamic modulation is taken into account. The author compares model results with scatterometer data, and discusses the consequences of model predictions for wave and current measurements by scatterometer, SAR, and ATI