Velocity measurement by refocusing approach in azimuth multi-angle spaceborne SAR imaging mode

In synthetic aperture radar (SAR) images, moving objects appear defocusing. Traditional azimuth velocity estimation methods ignore the displacement error caused by defocusing, which lead to the pixel offset measurement error among sequential images. In order to correct this error, a velocity measurement approach by moving target refocusing is presented in this paper. A novel azimuth multi-angle spaceborne SAR imaging mode is introduced to get sequential images, and effects of azimuth velocity on targets are presented as well. Moreover, azimuth velocity measurement method is derived to get the initial estimation value of the azimuth velocity. By using the initial estimation value, a refocusing approach is given, by compensating the quadratic residual phase and the time-shift phase caused by object moving. Consequently, a more precise azimuth velocity estimation result can be get by implementing the azimuth velocity measurement method again. Finally, the approach is verified by simulation of a point target with azimuth velocity.