Abstract
For the production of high quality images from synthetic aperture radar (SAR) received signal data, a method of suppressing and removing the degradation of SAR image range resolution caused by range migration is proposed and verified.
In spaceborne SAR systems, the response signal from each point on the earth surface spreads over several hundred range bins due to a spatial distortion known as range migration. This leads to the degradation of range resolution of SAR images produced by appling one dimensional matched filters in range and azimuth directions in the frequency domain.
A conventional method to solve the above problem is to apply a time invariant inverse filter to range compression in the frequency domain by neglecting that the degradation depends upon Doppler frequency and range distance of responce signal from each point on the earth surface. This can suppress only the bias term of the degradation of the SAR image resolution in the range direction.
In this paper, in order to remove the higher order terms of the degradation, the time variant inverse filter is additionally applied to azimuth compression in the time domain. This filtering is realized as the resampling to correct range migration in the azimuth compression. The filter function can be expressed as a three dimensional look up table. In this way the time variant filtering requires little additional computation load.
It is verified by the experiment using simulated SEASAT SAR data that for a look with maximum range migration the proposed method improves 2.0% of range resolution of SAR image against 1.3% which is obtained by the conventional method.
