Radar Results as Constraints on the Models of Venus.

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Abstract
The three significantly different models of the surface and atmosphere of Venus are apparently unresolvable with existing optical, infrared, and radio data. Briefly, these models may be described as: a CO2, N2' H2 0 atmosphere model, a dust-cloud model, and an ionospheric model. The radar observations around the 1961 inferior conjunction of Venus offer considerable information concerning these models, particularly for the ionospheric model. The primary data from the radar observations pertinent to this problem are the determinations of the reflectivity at 12.5 and 68 em of 10-15%, the lack of relative dispersion effects in delay times, the absorptivity at these two frequencies. In particular, the data show that the ion density at Venus must be less than about 5 X 108 cm-3. The required J'Ne2dz for the ionospheric model is about 1026 cm-5 forcing one to postulate a "hole" in the Venusian model over about 67% of the planetary disk around the anti-solar point. Such a structure would introduce phase effects in the disk temperature that are inconsistent with the observations. The relatively low reflectivity that has been observed in the radar experiments suggests a low dielectric constant (1-5) for the Venusian surface material which is most consistent with the dust model of the surface and atmosphere. However, the radar results strongly supporting the idea of synchronous rotation of Venus weigh against the dust model and tend to support the model containing water vapor and the associated greenhouse explanation of the observed disk temperature.

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