S-Band FMCW Radar Measurements of Ocean Surface Dynamics

Abstract

A ground-based frequency-modulated continuous wave microwave radar has been developed and applied to the measurement of ocean surface velocities. Full Doppler spectra are available, and both range and lime variations of the surface drifts can be recorded with resolutions down to 2.5 m and 0.3 s, respectively, over range extents of up to 1000 m. The ability of the radar to provide information over a wide range of sea conditions is demonstrated. These range from the identification of 5-cm scattering waves and their damping by a surface slick, to the propagation characteristics of long (?200 m) ocean waves in deep and shallow water. The longwave propagation is in accord with linear wave theory. The relationship of the backscattered power at low grazing angles to the wave features is also demonstrated. The consequences of measuring radial velocity components at low grazing angles with a narrow beam antenna are considered. In this situation, wave height spectra and the principal wave direction are well determined in a unimodal sea. However, this radar configuration will overestimate the angular spreading in highly directional seas. In the nearshore zone, velocity measurements can be used to quantify the evolution of shoaling waves and wave breaking.