Refractivity Biases in GNSS Occultation Data
An analysis of atmospheric refractivity profiles observed by the georesearch satellite CHAMP between May 2001 and October 2004 reveals a negative bias compared to ECMWF meteorological fields at altitudes below 5 km. In order to separate bias contributions caused by critical refraction from contributions induced by the receiver tracking process a comprehensive end-to-end simulation study was performed. The simulations are based on radiosonde profiles obtained aboard research vessel “POLARSTERN”. Within a subset of 3039 profiles recorded on the Atlantic Ocean between 60°N and 60°S, 1202 profiles (39.6%) are found with vertical refractivity gradients below the threshold value of −157 km−1. Critical refraction layers occur mainly between 1 km and 2.5 km altitude, above 3 km the occurrence of critical refraction can be disregarded. End-to-end simulations using these 3039 refractivity profiles confirm that four quadrant carrier phase extraction outperforms the two quadrant method currently implemented on CHAMP. Within regions of low signal-to-noise ratios “open-loop” tracking methods yield improvements with respect to the current “fly-wheeling” method.
KeywordsGlobal Position System Phase Noise Radio Occultation Radio Occultation Data Global Position System Radio Occultation
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- Ao CO, Hajj GA, Meehan TK, Leroy SS, Kursinski ER, de la Torre Juárez M, Iijima BA, Mannucci AJ (2003a) Backpropagation processing of GPS radio occultation data. In: Reigber C, Lühr H, Schwintzer P (eds) First CHAMP mission results for gravity, magnetic and atmospheric studies. Springer, Berlin, pp 415–422Google Scholar
- Marquardt C, Schöllhammer K, Beyerle G, Schmidt T, Wickert J, Reigber C (2003) Validation and data quality of CHAMP radio occultation data. In: Reigber C, Lühr H, Schwintzer P (eds) First CHAMP mission results for gravity, magnetic and atmospheric studies, Springer-Verlag, Berlin, pp 384–396Google Scholar
- Melbourne WG, Davis ES, Duncan CB, Hajj GA, Hardy KR, Kursinski ER, Meehan TK, Young LE, Yunck TP (1994) The application of spaceborne GPS to atmospheric limb sounding and global change monitoring. JPL Publication 94-18, Jet Propulsion Laboratory, Pasadena, CA, USAGoogle Scholar
- Reigber C, Lühr H, Schwintzer P, Wickert J (eds) (2004) Earth Observation with CHAMP: Results from Three Years in Orbit. Springer-Verlag, Berlin Heidelberg New YorkGoogle Scholar
- Vaisala (1989) Upper air systems: RS 80 radiosondes. Tech rep, Vaisala GmbH, HamburgGoogle Scholar
- Ward P (1996) Satellite Signal Acquisition and Tracking. In: Kaplan ED (ed) Understanding GPS: Principles and applications. Artech House, Boston, LondonGoogle Scholar