Single frequency processing of GPS radio occultations

de la Torre Juarez, Manuel and Hajj, G. A. and Kursinski, E. R. and Kuang, D. and Mannucci, A. J. and Romans, L. J. (2002) Single frequency processing of GPS radio occultations. Submitted to International Journal of Remote Sensing.

Abstract

Tracking of the radio signals broadcast by the Global Positioning System(GPS) satellites as they are occulted from a GPS receiver by the Earth's atmosphere can provide high resolution vertical profiles of atmospheric refractivity, temperature, and water vapour. Most implementations of this radio occultation technique use the 2 GPS frequencies to correct for ionospheric effects. However, during most soundings, one of the frequencies is degraded by the introduction of the so-called Anti-Spoofing (AS) encryption mode. An alternative retrieval method is dicussed in this work for periods when only one of the two frequency signals has good quality. This method uses only the frequency with higher signal-to-noise ratio. We illustrate the quality of the atmospheric profiles obtained from such single frequency retrievals using GPS/MET data from the periods where the AS was turned off and the two frequencies were available. The results enable to ensure the quality of a climate record of thousands of radio occultations collected by GPS/MET during the period with AS encryption, and data processing of future missions with similar constraints, like IOX, can be performed.