VHF/UHF-band SAR imaging using circular tracks

Low frequency synthetic-aperture radar (SAR) in combination with change detection techniques can be used to search for stationary ground targets. In particular, the method has shown a great potential when vehicle-size objects are obscured by foliage. However. one possibility is to improve the detection capabilities to increase the aperture angle of the radar data acquisition to make sure that the strong cardinal responses of a typical vehicle are registered. This implies an angle of at least 180° to include the strongest (broadside) response when the target orientations are unknown. HF-VHF SAR data (20-90 MHz) have earlier successfully been exploited on this and now tests have also been conducted with the airborne VHF-UHF SAR system LORA (220-430 MHz) using the maximum angle 360°, i.e. a full circle. A first look on this data set indicates a possibility to obtain an extended response signature from the hidden targets compared to the corresponding images generated from the linear tracks made during the same flight mission. The image processing of circular tracks becomes more complex and precise processing of the imaging geometry is necessary, i.e. both accurate navigation data as well as a dense digital elevation model (DEM) of the illuminated ground segment.