Abstract
The great improvements in power and sensitivity of radar plus the development of more refined and elaborate data analyses have made it possible to obtain a variety of information about the planets. Measurements now include not only simple range by time delay; velocity by Doppler shift; and radar cross section by power returned; but also the roughness of the planetary surface and its variation from place to place through the shape of the reflected spectrum and the extent of double reflection of circularly polarized signals; the axis and rate of rotation of the planet by Doppler broadening, tracking of spectral features, and other techniques; and the mapping of the planet surface by range‐gated (i.e. location by coupling range and velocity) spectrums. The principal results obtained have been a greatly improved value of the astronomical unit; a period of rotation of Venus of about 250 ± 50 days retrograde; a surface variability and roughness of Venus comparable with that of the moon; a very smooth surface on Mars; a somewhat rougher surface on Mercury; the existence of one shiny spot 1000 or more miles wide on Jupiter; and negligible effects from planetary ionospheres and the interplanetary medium.
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