Bistatic experiment with ultra-wideband VHF-band synthetic- aperture radar

We describe a bistatic ultra-wideband VHF-band SAR experiment and present measurement results. The bistatic SAR system, operating in the band 28-73 MHz, is based on CARABAS-II as airborne transmitter and LORA as ground-based receiver. Monostatic SAR data can also be acquired simultaneously. In September 2007, a measurement campaign was conducted in Switzerland with the ground-based receiver located on Mount Niesen in Berner Oberland. The objective was to investigate the hypothesis that the bistatic signal-to-clutter ratio for a vehicle in a background of forested terrain or urban environment increases as the bistatic elevation angle increases. Both mono- and bistatic SAR images have been formed using backprojection techniques. Images with bistatic elevation angle of 4° (quasi-monostatic case) show similar characteristics as the monostatic images. The images with bistatic elevation angle of 10° and 20°, however, indicate that the clutter level decreases over both forested and urban areas. Measurements show that the signal-to-clutter ratio for a truck vehicle in a forest background increases by up to 10 dB compared with the quasi-monostatic case. The corresponding increase in signal-to-clutter ratio for an urban background is 2-8 dB, with the higher value obtained for multi-level buildings. These observations indicate that target detection can be significantly improved by using bistatic VHF-band SAR geometries.