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Postprocessing of L1 GPS radio occultation signals recorded in open‐loop mode
Author(s) -
Sokolovskiy S.,
Rocken C.,
Schreiner W.,
Hunt D.,
Johnson J.
Publication year - 2009
Publication title -
radio science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.371
H-Index - 84
eISSN - 1944-799X
pISSN - 0048-6604
DOI - 10.1029/2008rs003907
Subject(s) - global positioning system , radio occultation , gps signals , remote sensing , computer science , inversion (geology) , phase locked loop , troposphere , demodulation , radio frequency , signal (programming language) , gnss applications , geodesy , assisted gps , geology , telecommunications , meteorology , physics , paleontology , channel (broadcasting) , structural basin , jitter , programming language
GPS Radio Occultation (RO) profiling from low‐Earth orbiting satellites is operationally used for numerical weather forecasting and is starting to be used for climate studies. Obtaining high‐quality observations near the surface requires recording of RO signals in model‐aided open loop (OL) mode by the GPS receiver. Postprocessing of the OL RO signals is different from that of the signals recorded in traditional phase‐locked loop (PLL) mode. It requires modeling of the signal frequency for connection of the phase between samples and removal of the GPS navigation data modulation (NDM). It is important that the postprocessing does not introduce errors (biases) in the connected phase. This paper describes the postprocessing of the OL RO signals which does not depend on the receiver model. The postprocessing includes: modeling of the RO signal frequency from refractivity climatology and the subsequent adjustment of this model by use of feedback which makes the postprocessing model‐independent; internal (as in PLL) removal of NDM and the use of externally recorded NDM bit sequence. Statistical comparison of the refractivity inversion results demonstrates that external demodulation of RO signals reduces the inversion bias in the tropical lower troposphere by about 0.5%.