Tyler/Abstract The objective of this research is to investigate the combination of propagation, meteorological, and measurement problems associated with an Earth occultation observing system. In comparison with exploratory measurements of other planets or measurements of less dynamic and complex atmospheres farther from the sun, occultation measurement of Earth's atmosphere is believed to present a considerable challenge. In the area of radio-wave propagation, we will investigate the effects on radio occultation measurements of: (i) local departures from spherical symmetry in the terrestrial atmosphere (e.g., due to weather fronts and baroclinicity); (ii) diffraction of radio waves, which will occur frequently in terrestrial occultations (e.g., due to small-scale gravity waves or abrupt refractive variations in the ocean boundary layer); (iii) multipath propagation, which occurs in connection with complex refractivity structures and is at a minimum an important factor in preventing reliable GPS/MET observations of the lowest several km of the atmosphere; and (iv) critical layers (i.e., ducts) in the basic refractivity structure, which fundamentally limit the region of the atmosphere accessible to remote sensing through radio occultation. With regard to item (ii), the standard retrieval algorithm (Abel inversion) for radio occultation data ignores diffraction effects and we will attempt to develop (and apply) a new algorithm that, by properly accounting for diffraction, can yield profiles at enhanced, sub-Fresnel-scale vertical resolution. These propagation effects will be studied with the dual objectives of better understanding radio occultation data already acquired with the GPS/MET instrument on Micro Lab 1 and of gaining insight toward the design of an advanced GPS receiver that can be used to collect radio occultation data on future satellite missions. With regard to the former, we will analyze a subset of GPS/MET data with emphasis on areas (e.g., studies of atmospheric waves) where the data have not yet been fully utilized.
