Quality assessment of COSMIC/FORMOSAT-3 GPS radio occultation data derived from single- and double-difference atmospheric excess phase processing

Abstract

This study evaluates the quality of GPS radio occultation (RO) atmospheric excess phase data derived with single-and double-difference processing algorithms. A spectral analysis of 1 s GPS clock estimates indicates that a sampling interval of 1 s is necessary to adequately remove the GPS clock error with single-difference processing. One week (May 2-8, 2009) of COSMIC/FOR-MOSAT-3 data are analyzed in a post-processed mode with four different processing strategies: (1) double-differencing with 1 s GPS ground data, (2) single-differencing with 30 s GPS clock estimates (standard COSMIC Data Analysis and Archival Center product), (3) single-differencing with 5 s GPS clocks, and (4) single-differencing with 1 s GPS clocks. Analyses of a common set of 5,596 RO profiles show that the neutral atmospheric bending angles and refractivities derived from single-difference processing with 1 s GPS clocks are the highest quality. The random noise of neutral atmospheric bending angles between 60 and 80 km heights is about 1.50e-6 rad for the singledifference cases and 1.74e-6 rad for double-differencing. An analysis of pairs of collocated soundings also shows that bending angles derived from single-differencing with 1 s GPS clocks are more consistent than with the other processing strategies. Additionally, the standard deviation of the differences between RO and high-resolution European Center for Medium range Weather Forecasting (EC-MWF) refractivity profiles at 30 km height is 0.60% for single-differencing with 1 and 5 s GPS clocks, 0.68% for single-differencing with 30 s clocks, and 0.66% for doubledifferencing. A GPS clock-sampling interval of 1 s or less is required for single-and zero-difference processing to achieve the highest quality excess atmospheric phase data for RO applications.

Evaluation of atmospheric profiles derived from single- and zero-difference excess phase processing of BeiDou radio occultation data from the FY-3C GNOS mission

“…( The GNSS satellite orbits (positions and velocities) and the GNSS clock offset estimates δt b,c are provided by the International GNSS Service (IGS) and applied as needed (a transformation from the International Terrestrial Reference Frame of IGS to our true-of-date reference frame is performed). Using the orbit information, the periodic relativistic effect of the GNSS satellite clock δt b,c rel can be modeled by (Schreiner et al, 2010) …”

“…In our processing we do not (yet) account for the small relativistic effects on the LEO (GNOS) clocks but investigate potentially including these effects in the future. The gravitational delay δρ b,c a,rel is modeled by (Schreiner et al, 2010) …”

“…Comparing with the original double-difference method (Ware et al, 1996;Rocken et al, 1997), the single-difference method uses the solved GNSS satellite clock offset estimates instead of further differencing between the GNSS satellites and a GNSS ground station; hence, the single-difference method can minimize the effects of ground data error sources Schreiner et al, 2010). Because single differencing (SD) needs no ground station data, the processing is simpler and easier to realize.…”

Evaluation of atmospheric profiles derived from single- and zero-difference excess phase processing of BeiDou System radio occultation data of the FY-3C GNOS mission

“…Comparing with the original double-difference method (Ware et al, 1996;Rocken et al, 1997), it uses the solved GNSS satellite clock offset estimates instead of further differencing between the GNSS satellites and a GNSS ground station, hence single-difference method can minimize the effects of ground data error sources during the 15 GPS clock offset estimation process Schreiner et al, 2010). Because singledifferencing needs no ground station data its data processing is simpler and easier to realize.…”

Integrating uncertainty propagation in GNSS radio occultation retrieval: from excess phase to atmospheric bending angle profiles

“…We set the transmitter position and velocity uncertainties to u , as found by ongoing rOPS-related POD studies (Innerkofler et al, 2016), consistent with previous literature (e.g., Montenbruck et al, 2009;Schreiner et al, 2009). …”