Analysis of Ground Tests of a Microwave, Earth-Occultation, Pressure-Reference-Level System

Abstract

Satellite infrared sounding instruments, such as SIRS and VTPR, generate temperature profiles as a function of pressure. A two-satellite, microwave, earth-occultation system can supplement an infrared sensor by providing an accurate altitude reference that will serve to fix, as a function of height, the derived temperature profile of the infrared sounder. This paper describes the results of ground tests made in Hawaii to estimate the likely effects of scintillation and fading on an occultation system. It was found that the microwave signal suffered periods of intense fading; extensive computer analyses of the data were performed in which aircraft-generated refractivity profiles were subjected to ray tracing. Results of these analyses indicate that the probable cause of the observed fading was multipath, a low-altitude phenomenon usually attributed to water vapor inhomogeneities. We maintain that multipath will therefore have minimal effect on the pressure-reference microwave occultation system, which would operate at a relatively high closest-approach altitude (?8 km).