Some Factors Affecting Electromagnetic Detection of Lunar Subsurface Water

Determination of the presence or absence of lunar subsurface water appears possible, from a satellite in orbit around the moon or from lunar surface measurements, by the use of inductive electromagnetic techniques. A number of plane-layered models of the moon have been analyzed to obtain values of reflection coefficient, surface impedance, apparent dielectric constant, and apparent conductivity, computed for a normally incident plane wave at frequencies in the range 104 to 108 Hz. The variation of these quantities with frequency is markedly dependent on the presence or absence of sub-surface water (in either liquid or "permafrost" form); that is, a fraction of one percent of water, for a wide range of materials that might exist on the moon, yields characteristic signals. The detection depth for the water-bearing layer (if it exists) ranges from tens of meters to at least one kilometer, depending on the characteristics of the layers; results for representative models are displayed. For certain lunar models an equipment resolution of at least as good as + 1 dB is required.