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Microwave radiometers (MWR) can be used passively, to get regolith's thickness, brightness temperature and dielectric constant. Apart from that, I have little idea of how the instrumentation's parameters affect the measurements.

So, the situation is as such. There are quite a few Earth-based remote sensing MWRs. Can I use them directly for a lunar orbiter? If not, what changes would these have to incorporate in order to be useful, if possible at all? Also, References would be helpful, since I am new to this.

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  • $\begingroup$ Can you add a link to an example where a passive microwave radiometer on earth is used to measure the thickness and dielectric constant of the regolith? Sounds difficult! $\endgroup$
    – uhoh
    Mar 17, 2016 at 10:55
  • $\begingroup$ Probably "estimate" or "infer" the thickness, rather than "get" or "measure". Dielectric constant should probably be an input parameter to the analysis (from lunar samples brought back to earth) rather than a measurement, at least by passive earthbound radiometry. $\endgroup$
    – uhoh
    Mar 17, 2016 at 13:17

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China's Chang'e 1 (CE-1) and Chang'e 2 (CE-2) lunar orbiters were both equipped with multi-channel microwave radiometers, measuring thermal emissions from the lunar surface and near-surface down to 30 meters of depth. Similarly, Chinese Yutu rover from the Chang'e 3 mission is equipped with a GPR that also operates in microwave frequencies. NASA, to my knowledge, hasn't yet used microwave radiometers in lunar orbit, but they do use them for other than Earth science missions, such as WMAP and Juno, has flown MiniSAR microwave Synthetic Aperture Radar on ISRO's Chandrayaan-1 lunar probe, will include a dual-frequency SAR on Chandrayaan-2, and MWRs might be included on future lunar polar landers such as Resource Prospector. Similar design instrument, but of course in a different electromagnetic spectra, is also LRO's Diviner in IR frequencies from 0.3 to 400 μm.

So the two Chang'e probes used the closest to if not exactly what you're inquiring about in lunar orbit. There's many papers published and freely accessible online on their mission, science return and to some extent discussing specifics of their design:

Also search Lunar and Planetary Institute's library, NASA Technical Reports Server, Google Scholar and so on for papers on related topics. Potentially also of interest might be the upcoming 47th Lunar and Planetary Science Conference, ISC's Lunar Polar Volatiles portal with schedule to own publicly accessible workshops and other related events of interest, and so on.

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