A technique is described to infer an estimate of the tropospheric radio refractive index distribution from earth-based observations of a satellite-borne beacon. This technique, known as the direct inference technique (DIT) predicts the refractivity profile by comparing the observed interference pattern, created as the satellite moves through low elevation angles, to patterns generated from a family of assumed refractivity profiles. It is shown that DIT correctly predicts the ducting environment for 12 of 22 satellite-to-ground RF measurements made during July and August 1978. Although the inferred profile geometry can differ significantly from the refractivity profile measured by an upper air sounding, the technique is moderately successful in predicting whether the true profile contains a ground-based or elevated duct. However, the overall reliability of predicting the dominant features of the duct (e.g., refractive gradient through the trapping layer, top height of the duct) is not adequate for operational usage.