High-resolution synthetic aperture radar observations of the moon

Variations in radar backscatter from planetary surfaces are related to differences in the local slope and the electrical and structural properties of the top surface layer. The top few meters of the surface of the Moon consist of fine-grained unconsolidated rock material containing exposed and buried rocks. Previous Lunar radar measurements have shown a depolarized backscatter component related to the abundance of surface and sub-surface rocks and a linearly polarized component associated with sub-surface backscatter.;A circularly polarized wave was transmitted and both senses of circular polarization were received. Stokes vector analysis was used to estimate the circularly and linearly polarized backscatter components. The comparison of these measurements to a model of quasi-specular and diffuse backscatter from surface and sub-surface structures yielded estimates of the surface dielectric constant and showed that subsurface quasi-specular scattering is required for this model to explain the linearly polarized backscatter power. Images of the Lunar poles show enhanced backscatter with a circular polarization ratio of approximately 0.9 from the radar facing inner walls and ejecta of several impact craters. This result is mainly attributed to diffuse backscatter from exposed and buried rocks. The orientation of the linearly polarized backscatter component was found to correlate with surface topography confirming that this component is, in general, the result of transmission through the surface. Results of an interferometric experiment showed that interferometric phase fringes related to topography can be generated from data acquired several months apart.;High spatial resolution observations of the Lunar surface were conducted using the Arecibo Observatory 12.6 cm wavelength radar in 1990 and 1992 with the aim of analyzing local variations in the surface backscatter properties. In the finest spatial resolution mode a pulsed pseudo-random code with a 10 MHz bandwidth was transmitted and approximately 24 minutes of data was processed to achieve pixel resolutions smaller than 40 m in both dimensions. To obtain this fine resolution over a large area, a focused delay-Doppler algorithm was developed. This new data processing method applies range and frequency offsets to the raw data that permit processing with an algorithm similar to that used for strip mode synthetic aperture radar.