Bistatic-Radar Techniques for Observing Long-Wavelength Directional Ocean-Wave Spectra

Bistatic-radar Bragg scattering of medium-to long-wavelength radio waves by ocean waves can be used as a means for observing directional ocean-wave spectra. Only moderate antenna directivity is required; areal and directional resolution are provided by high-resolution delay-Doppler processing of the radar echoes. Directional characteristics of long-wavelength (80-200 m) ocean waves have been observed using LORAN A transmission (1.85 MHz) and a receiver located 280 km from the transmitter. The received signals have been converted into a time-delay Doppler-frequency map and into a plot of normalized radar cross section σ0, as a function of directional ocean-wavenumber.