Geocenter coordinates estimated from GNSS data as viewed by perturbation theory.pdfVIP

Available online at Advances in Space Research 51 (2013) 1047–1064 Review /locate/asr Geocenter coordinates estimated from GNSS data as viewed by perturbation theory Michael Meindl ?, Gerhard Beutler, Daniela Thaller, Rolf Dach, Adrian Ja¨ggi Astronomical Institute, University of Bern, Sidlerstrasse 5, 3012 Bern, Switzerland Received 26 May 2012; received in revised form 29 October 2012; accepted 31 October 2012 Available online 9 November 2012 Abstract Time series of geocenter coordinates were determined with data of two global navigation satellite systems (GNSSs), namely the U.S. GPS (Global Positioning System) and the Russian GLONASS (Global’naya Nawigatsionnaya Sputnikowaya Sistema). The data was recorded in the years 2008–2011 by a global network of 92 permanently observing GPS/GLONASS receivers. Two types of daily solutions were generated independently for each GNSS, one including the estimation of geocenter coordinates and one without these parameters. A fair agreement for GPS and GLONASS was found in the geocenter x- and y-coordinate series. Our tests, however, clearly reveal artifacts in the z-component determined with the GLONASS data. Large periodic excursions in the GLONASS geocenter z-coordinates of about 40 cm peak-to-peak are related to the maximum elevation angles of the Sun above/below the orbital planes of the satellite system and thus have a period of about 4 months (third of a year). A detailed analysis revealed that the artifacts are almost uniquely governed by the di?erences of the estimates of direct solar radiation pressure (SRP) in the two solution series (with and without geocenter estimation). A simple formula is derived, describing the relation between the geocenter z-coordinate and the corresponding parameter of the SRP. The e?ect can be explained by ?rst-order perturbation theory of celestial mechanics. The theory also predicts a heavy impact on the GNSS-derived geocenter if once-per-revolution SRP parameters are estimated in the direc