HR: 0800h
AN: G21A-1262    [Abstracts]
TI: Laterally heterogenous troposphere: a possible explanation for seasonality in GPS coordinates time series
AU: * Houlie, N
EM: houlie@ipgp.jussieu.fr
AF: Institut de Physique du Globe Equipe de Sismologie, 4, Place Jussieu, Paris 05, 75252 France
AU: Briole, P
EM: briole@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris Equipe de Geodesie, 4, Place Jussieu, Paris 05, 75252 France
AB: The accuracy of the GPS solutions is still controversial after 15 years of intensive by the science community. In order to increase the accuracy of the daily GPS solutions, several investigations were focused on the analysis and interpretation of the vertical term of the GPS time-series, the oscillations being often attributed to oceanic loading effect (Dach et al., 2001; Van dam et al., 2001). However, this tidal effect cannot explain the amplitudes of the oscillations observed on the horizontal component of the time-series of permanent GPS stations for example from the EUREF network in Europe or the GEONET network in Japan (Hatanaka et al., 2003). We investigated the potential impact of the lateral variation of the meteorological parameters on the solutions of the GPS permanents benchmarks localizations to know whether such effect could be explained by a lateral heterogeneity of tropospheric delay. For that, we analyze the time series of seventy-one stations of the European Reference Frame (EUREF) GPS array. Our approach is based on the simple assumption that, for GPS sites located in a place with lateral heterogeneity of environment (site near the sea or near a mountain range), a systematic difference in wet tropospheric delay might exists in average over the year between rays travelling over sea and rays travelling over land. As higher temperatures produce larger delays, the heterogeneous effect is expected to be larger in summer than in winter thus to produce a bias of the horizontal coordinates variable over the year. For example, at a site characterised by an annual temperature excursion of ten degrees, one percent average lateral heterogeneity of relative humidity is enough to produce seasonal fluctuations of the horizontal coordinates of eight millimeters.
DE: 3311 Clouds and aerosols
DE: 3360 Remote sensing
DE: 3394 Instruments and techniques
SC: Geodesy [G]
MN: Fall Meeting 2005