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CARABAS
CARABAS is an innovative airborne synthetic aperture radar. It is characterized by operating with large fractional bandwidth in the regime of meter wavelengths. The name is an acronym for Coherent All Radio Band Sensing, indicating its exploitation of a large frequency segment within the VHF/UHF radio bands. The radar has been in development since 1985 during which three demonstrators have been produced and evaluated. CARABAS I was completed in 1993, CARABAS II in 1987 and CARABAS III in 2010. Typical radar bands exploited are 20–90 MHz and 140–370 MHz, which by synthetic aperture radar techniques yields a ground surface resolution 2.5x2.5 m and 0.7x0.7 m respectively. The low frequencies provide good penetration into vegetation and to some extent into the ground. In particular, the radar exhibits superior performance of object detection under thick tree canopies. Another application example is biomass estimation, since at the frequencies exploited it is the tree volume which decides the strength of tree radar response.

Realization of the radar has required a significant amount of innovative work. The development commenced in 1985 at the Swedish Defense Research Establishment under leadership of Hans Hellsten, who also was its originator. Later stages of development resulted in the much more compact CARABAS III and was carried out by Saab AB in Gothenburg, again technically led by Hans Hellsten.

For a scientific account of the technique, see: Hellsten H.: ”Meter Wave Synthetic Aperture Radar for Concealed object Detection”, Artech House, 2017.

For a general exposé of foliage penetration radars, see: Davis M.E.: “Foliage Penetration Radar – Detection and Characterization of Objects under Trees”, SciTech Publishing, 2011.