Adaptive time-frequency ISAR processing

Conventional radar processors use the Fourier transform to retrieve Doppler information. In order to use the Fourier transform adequately, some restrictions must be applied: the scatterers must remain in their range cells and their Doppler frequency contents should be stationary during the entire imaging time duration. If the Doppler frequency contents are time-varying, the Doppler spectrum obtained from the Fourier transform becomes smeared, and, thus, the image resolution is degraded. However, the restrictions on the Fourier processing can be lifted if the Doppler information can be retrieved with the time-frequency transform which does not require a stationary Doppler spectrum. Therefore, the image blurring caused by the time-varying Doppler spectrum can be resolved without applying sophisticated motion compensation techniques to the individual scatterers.