Miniature Synthetic Aperture Radar (Mini-SAR)

Description

The Miniature Synthetic Aperture Radar (Mini-SAR) is a small imaging radar designed primarily to map the scattering properties of the lunar poles in order to ascertain if water ice is present and if so, to determine its location and distribution. Concentrated ice exhibits an increase in radar reflectivity and enhancement of circular polarization ratio along the backscatter direction which can be measured by mini-SAR, allowing construction of a map of the location of ice deposits. Mini-SAR will also be used to produce radar maps of the lunar surface near the poles.

The mini-SAR transmits at a frequency of 2.5 GHz with a Right Circular Polarization (RCP) and receives both Left Circular Polarization (LCP) and RCP. Mini-SAR can function as either a scatterometer or a synthetic aperture radar (ASAR) In scatterometer mode, mini-SAR will point downwards (nadir-pointing) along the orbit ground track. The RCP and LCP returns will allow determination of the surface RF emissivity, near-normal incidence Fresnel reflectivity, meter-scale surface roughness, and circular polarization ratio. This informationwill give estimates of radar and physical surface parameters such as dielectric constant and porosity at a resolution of 1.2 Km/pixel. In SAR mode the system is directed 45 degrees off-nadir, imaging a swath parallel to the orbital track by delay / Doppler methods. A complete mosaicin both RCP and LCP, with a resolution of 150 meters, is compiled in roughly two weeks with a SAR swath taken every third orbit. A single SAR path will last less than 10 minutes. The SAR mode is used sparingly because the high data rate precludes operation of the other instruments during SAR operation. The instrument minimum antenna gain is 24.97 dB and peek RF power is 20 W. A bistatic radar experiment is also planned in concert with the Lunar Reconnaissance Orbiter to allow imaging of the poles at a non-zero phase angle, which could provide definitive evidence of lunar water ice.