Total reflection methods and instrumentation for their use are described for measurements of dielectric permittivity and loss at frequencies to 10 GHz or more. Several cell designs are shown, together with analyses of their performance. Procedures are given for correcting effects of wave propagation in the cells and residual reflections in the cells by bilinear analysis with calibrations using dielectrics of known permittivity. Representative results are presented for highly polar liquids, dilute solutions of polar molecules in nonpolar solvents, electrolyte solutions, and ionic glasses with appreciable ohmic conduction.

A simple model consisting of volume backscattering from within the lunar regolith can explain the observed diffuse component of lunar radar echoes. At a wavelength of 68 cm, a good match of the model with the data yields a value of 2.5–3 for the relative permittivity of the regolith in good agreement with the quasi‐specular backscattering estimates. The fit at 23 cm is poorer but yields a value slightly less than 2. At 3.8 cm, the value is below 1.5, and both that value and the 23 cm value are in good agreement with the radiometrically determined values at their respective wavelengths. These lower values at short wavelengths are probably a result of the rapid density increase with depth just at the surface. A slope‐dependent reflectivity can reconcile the values of relative permittivity obtained radiometrically and from the proposed diffuse backscattering model to those obtained from radar cross‐section measurements. There is some evidence that the permittivity of the rocks forming the lunar highlands may be lower than that of the rocks underlying the maria.

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