Quality Control Methods for Climate Applications of Geodetic Tropospheric Parameters

Abstract

AbstractWe have been analyzing the zenith total delay (ZTD) time series provided by six REPRO3 International GNSS Service (IGS) Analysis Centers (ACs), namely, COD, ESA, GFZ, GRG, JPL, and TUG, to compare their long-term trends. Long-term here means 20 years or longer. About thirty stations have been selected globally for this purpose. The estimated ZTD time series have gone through a process of homogenization using ERA-5 derived ZTDs as reference. The homogenized data is then averaged to daily values to minimize potential influences coming from different estimation strategies adopted by individual Analysis Centers as well as to mitigate the inherent autocorrelation. Similar averaging is applied to the ERA-5 ZTDs. Two combinations, using weighted mean and (a robust) least median of squares, are being generated from the six homogenized ACs. The combinations serve as quality control to each ACs. Analysis of the trends generated from each one of the seven ZTD time series is performed looking at their similarities in both time and frequency domains. This paper showcases the methodology and early results as presented during the second International Symposium of Commission 4: Positioning and Applications. Early results are based on station ALBH in Canada, showing an inter-AC scatter is 0.47 mm/decade for the trends, 0.11 mm for the annual amplitudes, and 0.29° for the annual phase.