Enhancement of doppler centroid for ocean surface current retrieval from ERS-1/2 raw SAR

Abstract

Ocean surface current information is one of the important factors which are employed for a variety of scientific pursuits especially on ocean environment. Although remote sensing techniques have been developed up to now, the investigation of ocean surface current using synthetic aperture radar (SAR) is not easy of access. This paper presents the results of ocean current observation using ERS-1 raw SAR data which were obtained off the coast of Jeju Island. We extract the ocean current based on the concept in which Doppler frequency shift and the ocean current are closely related. Moving targets cause Doppler frequency shift of the backscattered radar radiation of SAR, thus the line-of-sight velocity of the scatters can be evaluated. The Doppler frequency shift can be measured by estimating the difference between Doppler centroid obtained and reference Doppler centroid calculated. Theoretically, the Doppler centroid is zero, however, squinted antenna which is affected by several physical factors causes Doppler centroid to be nonzero. The Doppler centroid can be estimated from measurements of sensor trajectory, attitude and Earth model. By compensating ERS attitude errors, we could enhance Doppler centroid accuracy and verify that the extracted ocean surface current is more coincident with the in-situ data. We present here the results of estimated ocean surface current and observed in-situ data, which are in agreement within the limit of error bounds