HR: 1330h
AN: G52C-0050    [PDF]
TI: Laser, GPS and absolute gravimetry vertical positioning time series comparison at the OCA observatory, France
AU: Nicolas, J
EM: joelle.nicolas@tiscali.fr
AF: ESGT, 1, Bd Pythagore, Le Mans, F-72000 France
AU: Nocquet, J
EM: Jean-Mathieu.Nocquet@earth.ox.ac.uk
AF: Department of Earth Sciences University of Oxford, Parks Road, Oxford, OX1 3PR United Kingdom
AU: * Van Camp, M
EM: mvc@oma.be
AF: Royal Observatory of Belgium Seismology, Avenue Circulaire 3, Brussels, B-1180 Belgium
AU: Coulot, D
AF: ENSG/IGN/LAREG, 6-8 Av. Blaise Pascal Cit‚ Descartes Champs sur Marne CEDEX 2, Marne-la-Vall‚e, F-77455 France
AB: Time-dependent displacements of stations usually have magnitude close to the accuracy of each individual technique, and it still remains difficult to separate the true geophysical motion from possible artifacts inherent to each space geodetic technique. The Observatoire de la C“te d'Azur (OCA), located at Grasse, France benefits from the collocation of several geodetic instruments and techniques (3 laser ranging stations, and a permanent GPS) what allows us to do a direct comparison of the time series. Moreover, absolute gravimetry measurement campaigns have also been regularly performed since 1997, first by the "Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg, France, and more recently by the Royal Observatory of Belgium. This study presents a comparison between the positioning time series of the vertical component derived from the SLR and GPS analysis with the gravimetric results from 1997 to 2003. The laser station coordinates are based on a LAGEOS -1 and -2 combined solution using reference 10-day arc orbits, the ITRF2000 reference frame, and the IERS96 conventions. Different GPS weekly global solutions provided from several IGS are combined and compared to the SLR results. The absolute gravimetry measurements are converted into vertical displacements with a classical gradient. The laser time series indicate a strong annual signal at the level of about 3-4 cm peak to peak amplitude on the vertical component. Absolute gravimetry data agrees with the SLR results. GPS positioning solutions also indicate a significant annual term, but with a magnitude of only 50% of the one shown by the SLR solution and by the gravimetry measurements. Similar annual terms are also observed on other SLR sites we processed, but usually with! lower and various amplitudes. These annual signals are also compared to vertical positioning variations corresponding to an atmospheric loading model. We present the level of agreement between the different techniques and we discuss possible explanations for the discrepancy noted between the signals. At last, we expose explanations for the large annual term at Grasse: These annual variations could be partly due to an hydrological loading effect on the karstic massif on which the observatory is located.
DE: 1200 GEODESY AND GRAVITY
DE: 1243 Space geodetic surveys
DE: 1247 Terrestrial reference systems
DE: 1294 Instruments and techniques
SC: Geodesy [G]
MN: 2003 Fall Meeting