The GPS Radio Occultation Concept: Theoretical Performance and Initial Results

Citation

Kursinski, Emil Robert (1997) The GPS Radio Occultation Concept: Theoretical Performance and Initial Results. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/HPMZ-6524. https://resolver.caltech.edu/CaltechTHESIS:01282013-095417825

Abstract

Implementation of the Global Positioning System (GPS) network of satellites and small, high performance instrumentation to receive GPS signals have created an opportunity for low cost, active remote sounding of Earth's atmosphere by radio occultation. The first goal of the present research is to estimate the spatial coverage, resolution and accuracy expected for atmospheric profiles derived from GPS occultations. Typically, vertical resolution ranges from 0.5 km in the lower troposphere to 1.4 km in the middle atmosphere. Useful profiles of refractivity should be derivable from ~60 km altitude to the surface with the exception of regions less than 250 m in vertical extent associated with high vertical humidity gradients. Above the 250 K altitude level in the troposphere, where the effects of water are negligible, sub-Kelvin temperature accuracy is predicted up to ~40 km depending on the phase of the solar cycle. Predicted accuracy of geopotential heights of constant pressure levels is ~10 m or better between 10 and 20 km altitudes. Deep in the warm troposphere the contribution of water to refractivity becomes sufficiently large for the accurate retrieval of water vapor given independent temperatures from weather analyses. We discuss several applications of the unique qualities of the technique including numerical weather prediction and long term monitoring of Earth's climate.

The second goal is to demonstrate some features using data from the prototype GPS-MET occultation investigation. We demonstrate ~1 km vertical resolution and temperature consistency with global weather analyses generally at the 0.5 to 1 K level. We discuss some initial observations of equatorial waves in the lower stratosphere and possible implications for exchange between the troposphere and stratosphere. During the June-July 1995 period, occultations typically extend to within 1 to 3 km of the surface and are used to derive a brief climatology of water vapor in latitude versus height, the first truly global view of water vapor at ~1 km vertical resolution. A low latitude bias structure in the weather analyses is revealed centered near 2 km altitude where analysis humidities are larger than those derived from the occultations in the subtropics but smaller in the tropics apparently associated with a systematic error in the boundary layer height in the analyses.

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