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Seasonal effect on vertical positioning by Satellite Laser Ranging and Global Positioning System and on absolute gravity at the OCA geodetic station, Grasse, France

Abstract:

We present a comparison of the vertical displacement monitored by independent techniques at the geodetic observatory of Grasse (France). Both Satellite Laser Ranging and Global Positioning System (GPS) vertical position time-series over the period 1998-2003 show a prominent annual signal with a magnitude of 5-6 mm and reaching a maximum every year in July. Results from 14 absolute gravity measurements are also discussed. We investigate the possible origin of the observed signal by comparing it with pbkp_redictions from various local and regional contributions. GPS results from a local network indicate that the periodic annual elastic deformation of the ∼1270 m high karstic plateau due to local water storage loading does not exceed 1-2 mm. In contrast, a combination of global model pbkp_rediction for atmospheric and hydrological loading explains more than 70 per cent of the annual and semi-annual observed signals. © 2006 The Authors Journal compilation © 2006 RAS.