Delay-Doppler analysis of bistatically reflected signals from the ocean surface: Theory and application

We present a new stochastic theory for delay-Doppler mapping of the ocean surface for bistatic scattering. This stochastic theory should complement nicely the previous theories for the Global Positioning System (GPS) reflected signals from ocean surfaces, especially that of Zavorotny and Voronovich. We quantify the Doppler spread of the reflected signal before interpreting the delay. Our theoretical results compare very well to Doppler spectra computed using data collected during an airborne campaign. The bandwidth of the spectra is linked to the geometry and to the ocean roughness. The bulk of the Doppler spread is caused by the rms slope and not by the surface orbital velocity. Our stochastic theory is generalized to include the delay mapping made possible by the existence of the pseudorandom noise code on the GPS L-band carrier. These results can be seen as a generalization of Woodward's theorem for FM signals to delay-Doppler analysis of more complicated signals. Our formulation Is amenable to inversion for the determination of geophysical parameters such as surface wind vector and mean sea level. Another novelty in our approach is the inclusion of the sea state.