Improved Accuracy of Velocity Estimation for Cruising Ships by Temporal Differences Between Two Extreme Sublook Images of ALOS-2 Spotlight SAR Images With Long Integration Times

A method for improving the estimation accuracy of the velocity of cruising ships is proposed using synthetic aperture radar (SAR) sublook images in the spotlight mode. The main purpose of spotlight SAR is to obtain high resolution utilizing longer integration times than those of other imaging modes, and the proposed method is based on these long integration times. The principal methodology is to produce successive
N
sublook images of a cruising ship, where
N
is more than approximately 10. The positions of the look-1 and look-
N
subimages differ by a substantial distance proportional to the cruising speed and the long interlook time difference. The distance, and hence the velocity of the cruising ship, can be computed from the cross-correlation function of these two sublook images with improved accuracy compared with other modes. We tested using PALSAR-2 spotlight subimages with
N
= 2, 10, and 20, and the results are compared with the automatic identification system data. Five images of ships cruising close to the azimuth direction were tested; the best result was obtained for the 10-look images with an average error of 13.8%, followed by 17.9% and 40.5% errors for the 20- and 2-look images, respectively. The reason is also given for the best result of the 10-look case over the 20-look case.