The use of random frequency-hopped waveforms for the recovery of motion-degraded SAR imagery

There is a conflict between the requirement of a very low RCS target support system, and the need for high stability and accurate target setting during the SAR imaging of signature-critical targets. To meet the ideal of measuring targets in free space, multiple string suspension systems from overhead gantries have been devised. Despite measures to the contrary, air turbulence and mechanical vibration can produce complex perturbations of the target during the SAR imaging process. Model code was written to provide representative motion models. Simulations were made over a wide range of motion patterns to assess the effects on the imagery. The pattern of the image degradation has a complex dependence on the frequency sampling rate and characteristic period of the oscillation. A comparison is made between monotonically stepped-frequency waveforms and random frequency-hopped waveforms, and the benefits to image recovery of the latter discussed.