RESSAC: a new airborne FM/CW radar ocean wave spectrometer

The RESSAC radar system, used from aircraft platforms for measuring directional spectra of ocean waves in the gravity domain (wavelengths from 30 to 400 m), is presented. The instrument consists of a C-band (5.35-GHz) FM/CW radar system. The transmitting and receiving antennas look toward the surface at a low incidence angle (≈14° for the center of the antenna beam) and rotate around a vertical axis. When the data are processed, the known antenna gain pattern is removed from the recorded signal, making it possible to estimate the sea surface slope variance, which in turn is used to determine the tilt modulation transfer function, without the need of any external wind measurement. Fully normalized spectra obtained from RESSAC are compared to other data sets