How to Measure Surface and Atmospheric Conditions on Venus by Microwave Interferometry

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Predictions of the polarized and unpolarized interferometric visibilities of Venus are made for wave- lengths from 3 cm to 100 cm. The basis for the predictions is a multiparameter planetary model of brightness temperature. We reviewed Earth-based and spacecraft observations of Venus to establish particular values of all parameters in the general model, thus yielding a reference modeL We also used experimental interferometric results at 11.1 cm, reported in a companion paper, to help select the parameter values of the reference model. Interferometry over a range of wavelengths can establish the values of significant planetary parameters which at present are known only approximately. In order to assist planning such observations, we have made sensitivity calculations, varying the planetary parameters from their reference model values. Short interferometer baselines, at which the unpolarized visibility is near its first null, yield optimum parameter sensitivities; thus extensive high-resolution mapping is unnecessary. Measurements of the visibilities with an accuracy on the order of 0.001 of the total planetary flux (1 mvis) are necessary to improve estimates of the planetary parameters. For instance, at 21 cm, an increase in the surface dielectric constant from 3.9 to 4.1 changes the polarized visibility by 1.5 mvis. For 11.1-cm wavelength and the reference-model parameters, surface-temperature variations with latitude and longitude cause changes in the visibilities of about 1 mvis for each percent the maximum temperature varies from the mean.