1982 年 2 巻 4 号 p. 45-56
The synthetic aperture radar (SAR) images produced from the Seasat SAR data have provided useful all-weather topographical information. In order to produce a SAR image, the raw data is compressed by the action of matched filters, first in the range direction, then in the azimuth direction. The estimation error in a coefficient of the azimuth matched filter, called Doppler rate, causes image slip between looks. The image slip gives rise to most degradation of SAR multi-look image in look summation operation.
In order to reduce the degradation and produce a high resolution SAR multi-look image, an image slip detection type auto-focusing will be effective on condition that the precisely measured image slip data is given.
One of the conventional image slip measurement method is based on the cross-correlation between two looks of one scene. But, it is dependent on the characteristics of the scene.
This paper describes an improved method called three looks correlation. In this method, the measurement error is reduced by measuring and selecting the image slip among three looks of various scenes. The results of the Doppler rate auto-focusing tests show that the proposed method can reduce the measurement error by half in comparison with the conventional one.