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. This technique was tested using the JPL AIRSAR along-track interferometer. Measurements of the ocean coherence at the L-band were made at high spatial resolution under a variety of conditions. A new operating technique that results in the required two baselines is described. Some parametric analysis is performed pertaining to the design of such a system. A representative interferometric data set acquired at the Strait of Messina in 1991 is presented to illustrate the technique. The interferometric phase data reveal and measure tidal currents flowing through the strait, while the coherence time image shows considerable structure not visible in the backscatter or phase image. Coherence times in and around the strait were measured to be of the order of 0.1 s at the L-band, which is in agreement with previous estimates and measurements