First Results from the South African Vhf Imaging Radar

Abst ract:-The South African Sythetic Aperture Radar System (SASAR) was conceived of as a fully polarimetric, multifrequency, airborne SAR. System design work was carried out at the Radar Remote Sensing Group of the Department of Electrical Engineering, University of Cape Town, starting in 1993. Construction of flight hardware was contracted out to Industry and on board integration was given to the Aerotek division of the South African CSIR. Initial plans were based on the use of a South African Air Force Boeing 707. However, this fleet of aircraft became less and less accessible due to increased diplomatic use, and after considerable delays, a decision was made to move to a more available aircraft, a turboprop version of the DC3 (Dakota). Lack of funding had already resulted in only the fully polarimetric VHF sensor being constructed. The VHF sensor was seen as an important research tool for both foliage penetration studies, geological survey and maritime patrol applications. The low backscatter from most natural vegetation ensures that the VHF sensor operates as a good detection system for large, specular reflectors, especially man-made structures. This is borne out by other systems operating in this band, as well as our early results. UCT has developed two versions of a motion compensated, range-Doppler SAR processor. The standard version of the software is capable of medium resolution VHF processing (sufficient for the bandwidth of the present VHF system). The extended version can handle high resolution VHF processing should the bandwidth of the sensor be extended. Budget cuts for experimental flying resulted in further delays and the system was finally flown in early January, 1999. A long flight (close to 2000km) over varied terrain was made, and this paper reports on some of the preliminary results. Operation in the VHF Band makes the system victim to heavy levels of interference. A major part of the signal processing is the removal of this interference. A brief overview of the methods used is given, with comparison between a simple notch filter and a more complex LMS method. The interference suppression step has been included in the range processing step of the SAR processor, which gives a large improvement to the time taken for this suppression. The paper expands on the topics discussed above and presents some of the early results obtained. Future plans for the system are discussed. Key-Words:Radar, imaging radar, SAR, VHF radar, foliage penetration, radar geology CSCC’99 Proc.pp.4521-4527