Estimating ocean coherence time using dual-baseline interferometric synthetic aperture radar

A new technique for measuring the coherence time of the ocean surface at radar wavelengths has been developed and tested. This technique requires an interferometric synthetic aperture radar system with at least two unique baselines along the direction of platform motion. The coherence time of the surface may be presented as a high resolution coherence time map. In addition to the coherence time, the interferometric SAR information also provides the radar backscatter and mean Doppler shift for each pixel of the coherence time map. This tezhnique was tested using the JPL AIRSAR along-track interferometer. Measurements of the ocean coherence at L and C bands were made at high spatial resolution under a variety of conditions. Fundamental to this measurement is the ability of the AIRSAR system to image the ocean interferometrically at two different baselines, A new operating technique which allows this is described in here. Some parametric analysis is performed pertaining to the design of such a system. An example interferometric data set acquired at the Strait of Messina is presented to illustrate the technique. These data reveal and measure tidal currents flowing through the strait. Coherence times in and around the strait are of the order of 0.1 seconds at L band, which is in agreement with previous estimates and measurements. Considerable structure is observed in the amplitude (standard SAR), phase (Doppler) and coherence time imagery.