A primary objective of future Europa studies will be to characterize the distribution of shallow subsurface water as well as to identify any ice-ocean interface. Other objectives will be to understand the formation of surface and subsurface features associated with interchange processes between any ocean and the surface as well as regional and global heat flow variations. Orbital radar sounding, a now maturing technology, will be an essential tool for this work. We review the hypothesized processes that control the thermal, compositional, and structural properties, and therefore the dielectric character, of the subsurface of Europa's icy shell. We introduce fundamental concepts in radar sounding and then assess analog processes represented by, and sounded in, Earth's ice sheet. We use these Earth analog studies to define the radar imaging approach for Europa's subsurface that will be most useful for testing the hypotheses for the formation of major features.
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