Miniature Synthetic Aperture Radar (Mini-SAR – NASA)
Mini-SAR was designed, built and tested for NASA by a team including the Naval Air Warfare Center, Johns Hopkins University Applied Physics Laboratory, Sandia National Laboratories, Raytheon and Northrop Grumman, with support from ISRO. It was an active synthetic aperture radar built to search for lunar polar water ice.
The instrument transmitted right-polarised radiation at 2.5 GHz and monitored the scattered left and right polarised returns. The Fresnel reflectivity and circular polarisation ratio (CPR) are the key parameters deduced from these measurements: ice exhibits the Coherent Backscatter Opposition Effect, which enhances reflections and CPR, allowing the water content of polar regions to be estimated.
Mini-SAR imaged many of the permanently shadowed regions at both lunar poles. In March 2010, it was reported to have found more than 40 permanently darkened craters near the north pole hypothesised to contain an estimated 600 million tonnes of water ice — consistent with findings from M3 and NASA's LCROSS impactor.