Earth-Based Radar Studies of Planetary Surfaces And Atmospheres

Radar has been used as a remote sensing tool since 1946 when the first echoes from the moon were detected by ground-based radar systems. Since then the sensitivity of our most powerful radar systems has increased by a factor of about 1012, and radar studies of Mercury, Venus, Earth's moon, Mars, the Galilean moons of Jupiter, the rings of Saturn, and a dozen asteroids have been made. Specific studies range from simple measurements of distance or reflectivity to detailed maps or images of reflectivity, altimetry, and various other model parameters. This paper presents a short review of the more recent observations, and summarizes current research activities associated with each body. An attempt is made to anticipate the observational data set that should be available during the next decade. Such data will be useful for remote sensing applications, either directly or combined with data from other programs. The usefulness of the radar data is also dependent upon theoretical models that explain the observed scattering. Such models often are dependent upon parameters that are not measurable by radar. Likewise, models that predict other physical measurements may be influenced by parameters that are easily measured by radar. Thus many more exciting applications of radar data should become apparent as further observations are made by other techniques and as models are developed to explain the observed quantities.