Recovery of badly motion-degraded SAR imagery by the use of frequency-randomized waveforms

The use of SAR imaging is an important tool in the laboratory RCS characterization of signature critical platforms. Despite measures to the contrary, air turbulence and mechanical vibration can produce complex perturbations of the target during the imaging process. Model code was written to provide simulations over a wide range of representative target motions and imaging schemes. The slow swept-frequency data collection schemes of many laboratory radars mean that the target can undergo significant motion during and between pulses, leading to substantial and time-varying defocusing of range profiles. Conventional motion-correction schemes cannot be used as they rely on the presence of clearly defined range profiles which can be tracked over the imaging process. It was found that replacement of a monotonically increasing frequency waveform with one in which the frequency sampling order was repeatedly randomized could produce a significant recovery of the imagery, especially in combination with data averaging. The pattern of the image degradation was found to have a complex dependence on the radar waveform scheme and target motion characteristics.