From the PDS introduction to the S-Band Radar Images:
This data set contains dual-polarization backscatter maps of the lunar nearside collected at a wavelength of 12.6 cm (S-band), using the 305 m Radio Telescope at Arecibo to transmit and the NRAO's 105 m Robert C. Byrd Green Bank Telescope to receive. The data were provided by Bruce Campbell of the Smithsonian Institution's Center for Earth and Planetary Studies and archived by the PDS Geosciences Node.
The index map for the new 12.6 cm radar images is a large file. So I've down-loaded it and made it smaller so that you can easily identify which detailed image to look to see pieces of the limb.
There are three different versions of these radar images:
- OCP - polarized
- SCP - unpolarized
- CPR - polarization ratio
From the PDS Read Me file for this data:
'Polarized' refers to energy scattered from the lunar surface in the opposite circular polarization sense to that transmitted (the behavior expected of a flat, mirror-like reflecting surface). 'Depolarized' refers to reflected energy with the same sense of circular polarization (the behavior expected from a surface with abundant wavelength-scale objects that randomize the reflected polarization). And, I'll add, the "polarization ratio" is simply the ratio of those two images.
For me, the best combination of topography and surface characterization comes from the scp images. Here is the beginning of a list to download each 3 to 6 MB file: