Multi-Mission Multi-Center Level 1 Data Inter-Validation towards Wegener Center Reference Occultation System Reprocessing
Presenter:
Josef Innerkofler (1,2)
(1) Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics and Meteorology/Institute of Physics, University of Graz, Graz, Austria; (2) FWF-DK Climate Change, University of Graz, Graz, Austria
(1) Wegener Center for Climate and Global Change (WEGC) and Institute for Geophysics, Astrophysics and Meteorology/Institute of Physics, University of Graz, Graz, Austria; (2) FWF-DK Climate Change, University of Graz, Graz, Austria; (3) EUMETSAT, Darmstadt, Germany; (4) Astronomical Institute, University of Bern (AIUB), Bern, Switzerland; (5) COSMIC Program, UCAR, Boulder, CO, USA
Talk
GNSS Radio Occultation (RO) is a highly valuable remote sensing technique of the Earth’s atmosphere due to its global coverage, long-term stability, and essentially all-weather capability. In order to fully exploit its potential and to ensure highest quality of the derived key climate variables, such as temperature, pressure, and tropospheric water vapor, WEGC’s new Reference Occultation Processing System (rOPS) applies quality control and uncertainty estimation at each stage of the processing, starting with the Level 1 data processing, from the occultation geometry determination to excess phase derivation.
The occultation geometry subsystem uses GNSS orbit and clock data from the GNSS orbit data archives of CODE and IGS, and employs Bernese (v5.2) and Napeos (v.3.3.1) software packages for the Precise Orbit Determination (POD) of RO satellites in Low Earth Orbit (LEO). We perform a mutual consistency check of the orbit solutions including estimates of systematic uncertainty bounds and propagated random uncertainties. Furthermore, the obtained orbit and clock products are compared against external orbit and clock solutions (from EUMETSAT, UCAR, and AIUB) and, as possible, to radial position estimates from satellite-laser ranging (ILRS archive). Resulting monthly statistics show an overall consistency within RO LEO orbit uncertainty target specifications of 5 cm in position and 0.05 mm/s in velocity for the Metop-A/-B, GRACE, and CHAMP missions. However, degraded observation data, detected by the rigorous consistency evaluation of the quality of the calculated orbit and clocks, can at times lead to decreased accuracy estimates.
In the excess phase processing, we use two differencing approaches to eliminate the transmitter and receiver clock biases: 1.) zero-differencing for satellite missions with a sufficiently stable LEO clock (Metop, GRACE, and FengYun-3); 2.) single-differencing using additional observations from a non-occulting reference GNSS satellite for LEO clock correction (COSMIC, CHAMP, and SpireRO). Monthly inter-validation results between the rOPS excess phase profiles and external profiles provided by EUMETSAT and UCAR show high consistency. In addition, the excess phase profiles are compared against forward modeled excess phases based on ECMWF short-range forecast fields for quality control and estimating the uncertainty of the measurements. First results of the Level 1 processing of RO measurements from the FengYun-3 (from NSSC Beijing) and SpireRO satellites within the WEGC framework are also presented.
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