Compensating the effects of target acceleration in dual-channel SAR-GMTI

The authors examine the influence of uncompensated target acceleration on the focusing of moving targets in airborne synthetic aperture radar (SAR) imagery and present one method of detecting and compensating for its effects. Although vehicles travelling on roads and highways routinely experience acceleration, the majority of ground moving target indication algorithms assume a constant velocity scenario, which may result in a defocused target response. Both along-track and across-track accelerations are examined through simulations and experimental data from Environment Canada´s airborne CV 580 dual-channel SAR system. Acceleration can have severe effects on focusing and may result in azimuthal shift, azimuthal smearing and a significant loss in peak power in the SAR image. Having determined the effects of acceleration, time-frequency (TF) analysis implementing the pseudo-Wigner-Ville distribution is used to improve target focusing and to detect the presence of significant acceleration. Accelerating targets in experimental airborne data are presented and are identified as such by their non-linear TF histories. Estimations of the instantaneous frequency of the signals yield reconstructed target phase histories, which may be used to identify the presence of certain acceleration components and to obtain a focused image of each target. However, estimates of a target´s acceleration and velocity vector may not be uniquely determined using only two receive channels.