Comment on “Regolith Layer Thickness Mapping of the Moon by Radar and Optical Data,” by Y. G. Shkuratov and N. V. Bondarenko

In a recent Icarus article, Shkuratov and Bondarenko (2001) propose a model for the depth of the lunar regolith based on 70-cm radar observations and near-infrared spectroscopy. This model treats the regolith as a single homogeneous layer of lossy dust, and ignores scattering by buried rocks. There is also an implicit assumption that the regolith substrate is everywhere of uniform morphology. Radar scattering from this substrate is treated using averaged Fresnel coefficients, with little explanation of how such a model might produce the observed lunar polarization properties. Taken together, these issues weaken the validity of the published regolith depth map.