Noise characteristics in Zenith Total Delay from homogeneously reprocessed GPS time series
Anna Klos1, Addisu Hunegnaw2, Felix Norman Teferle2, Kibrom Ebuy Abraha2, Furqan Ahmed2,a, and Janusz Bogusz11Military University of Technology, Faculty of Civil Engineering and Geodesy, Warsaw, Poland 2University of Luxembourg, Geophysics Laboratory, Luxembourg acurrent address: Center for Space Research, University of Texas at Austin, USA
Received: 24 Nov 2016 – Accepted for review: 06 Dec 2016 – Discussion started: 06 Dec 2016
Abstract. Zenith Total Delay (ZTD) time series, derived from the re-processing of Global Positioning System (GPS) data, provide valuable information for the evaluation of global atmospheric reanalysis products such as ERA-Interim. Identifying the correct noise characteristics in the ZTD time series is an important step to assess the "true" magnitude of ZTD trend uncertainties. The ZTD residual time series for 1995–2015 are generated from our homogeneously re-processed and homogenized GPS time series from over 700 globally distributed stations classified into five major climate zones. The annual peak of ZTD data ranges between 10 and 150 mm with the smallest values for the polar and Alpine zone. The amplitudes of daily curve fall between 0 and 12 mm with the greatest variations for the dry zone. The autoregressive process of fourth order plus white noise model were found to be optimal for ZTD series. The tropical zone has the largest amplitude of autoregressive noise (9.59 mm) and the greatest amplitudes of white noise (13.00 mm). All climate zones have similar median coefficients of AR(1) (0.80 ± 0.05) with a minimum for polar and Alpine, which has the highest coefficients of AR(2) (0.27 ± 0.01) and AR(3) (0.11 ± 0.01) and clearly different from the other zones considered. We show that 53 of 120 examined trends became insignificant, when the optimum noise model was employed, compared to 11 insignificant trends for pure white noise. The uncertainty of the ZTD trends may be underestimated by a factor of 3 to 12 compared to the white noise only assumption.
Klos, A., Hunegnaw, A., Teferle, F. N., Abraha, K. E., Ahmed, F., and Bogusz, J.: Noise characteristics in Zenith Total Delay from homogeneously reprocessed GPS time series, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-385, in review, 2016.