AnnRep2003 to NKG-WGG

Space Geodesy Activities 2003

Report to the Nordic Geodetic Commission, Working Group for Geodynamics

The major profile of activities in Space Geodesy at Chalmers concerns atmosphere
remote sensing using microwave radiometry, GNSS and other satellites, and VLBI.
This report concentrates on solid earth applications.

Earth Rotation

An important research topic for geodetic VLBI is the investigation of variations in the earth’s
rotation and the interaction with geodynamical processes in the earth’s spheres, i.e. the
atmosphere, the oceans and the earth’s interior. Figure 1 shows the variations in length-of-
day, i.e. the excess of a constant length of day of 86,400 s. Clearly visible are the strong
El-Niño events in 1983 and 1997/1998 (positive excess) and the La-Niña event in 1989
(negative excess). These events are large-scale mass redistributions in the tropical ocean-
atmosphere system and influence the rotation of the solid earth. VLBI is the only technique
that can observe earth rotation with long term stability and is thus an important source of
information for a better understanding of global geodynamical processes.

The BIFROST GPS Project

Continuous GPS observations are used to infer deformation of the earth crust. In previously
presented results we have been able to conclude interstation velocity at a resolution of less
than 0.1 mm/yr in the horizontal and 0.2 to 0.3 mm/yr in the vertical coordinates (Scherneck
et al. 2003).
The networks of stations that form the instrumental basis for BIFROST extend throughout
the Baltic Shield area. The primary process leading to crustal deformation in this area is
glacial isostatic rebound, i.e. the slow creeping of the earth mantle that gradually will attain
equilibrium, the disequilibrium having been created in the succession of the melting of the
Pleistocene ice sheet in Fennoscandia. This process started roughly 20,000 years before
present. The motions that we observe in BIFROST can be reconciled with model compu-
tations employing visco-elastic earth structure and an ice history. Figure 2 shows a viscosity
profile of the mantle resolved by BIFROST (Milne et al. 2004).
The GPS-inferred motion presents a unique type of information. Traditionally, postglacial
rebound has been studied on behalf of its vertical component, using geological height
markers and sea level observations. The change of sea level, however, is composed of
oceanic and solid earth contributions, each of them covering a range of scales in time and
space; some important signatures are difficult to discern in time series, and some indicators
are known to have large systematic offsets. GPS measurements, on the other hand, have
demonstrated its advantages as it can (1) uniformly cover a wide geographic area with a
reasonable station spacing, (2) measure vertical position independent of sea level, and (3)
observe horizontal deformation.

GPS Reprocessing
The GPS networks in our area are SWEPOS in Sweden, FinnRef in Finland, SATREF in
Norway, and additional stations are operated in a continuous mode in Denmark, Russia, and
the Baltic states. The infrastructure, equipment, and performance have, especially since the
end of 1996, become very stable. During 2003 special efforts have been devoted to the GPS
derived motions by adding new analysis strategies and thus strengthen the reliability of the
result. A new GPS analysis software package (GAMIT/GLOBK) has been implemented
and five years of data (mid 1998 to mid 2003) have been analysed. In this analysis the
BIFROST network has been extended to include stations also from Norway, Denmark and
the Baltic countries. This extension is significant as it encompasses now almost all of the
area of postglacial uplift. Derived station velocities agree in general with former result to
better than 1 mm/yr in a very preliminary analysis. Some inconsistencies in the former
results have also been removed by the new analysis.

Ocean Tide Loading
The Space Geodesy group runs an Internet service that provides parameters for ocean tide
loading. The phenomenon concerns the deformation of the earth surface under the changing
pressure of the water load in the tidal oscillations in the oceanic basins of the Earth. The service
is available at http://holt.oso.chalmers.se/loading. Until March 2004 the service has been
called 1863 times to deliver parameters for a total of 32476 geographic locations.

Publications

2003
.

Bengtsson, L., G. Robinson, R. Anthes, K. Aonashi, R. Bingley, P. Cannon, A. Dodson, G. Elgered, G. Gendt, R. Gurney, M. Jitai, N. Latham, C. Marquardt, C. Mitchell, M. Mlaki, J. Nash, D. Offiler, A. Rhodin, P. Silvestrin, R. Ware, R. Watson, W. Wergen
Meeting Summary: Workshop on the use of GPS measurements for water vapor determination,
Bull. American Meteorological Soc., 84(9),
1249-1258, 2003.

Elgered, G., B. Stoew, L. Gradinarsky, and H. Bouma,
Analysis of atmospheric parameters derived from ground-based GPS
observations,
Proc. International Workshop on GPS Meteorology, Tsukuba,
Japan, Jan. 14-17, eds. T. Iwabuchi and Y. Shoji, Japan Meteorological Agency, 2003.

Elgered, G., and B. Stoew,
IVS Tecnical Development Center Onsala Space Observatory,
in International VLBI Service for Geodesy and Astrometry 2002
Annual Report, NASA/TP-2003-211619, eds. N. R. Vandenberg and K. D. Baver, pp. 311-313, 2003.

Elgered G., H.-P. Plag, H. van der Marel, S. Barlag, and J. Nash,
Ground-Based GPS for Climate and Numerical Weather Prediction Applications,
The Eggs, Newsletter and Information Service of the EGU, Issue 4, pp. 22-24, http://www.the-eggs.org/, June 2003.

Elgered, G., L. Gradinarsky, N. Gustafsson, J. Johansson, M. Ridal, and B. Stoew,
Meteorological Applications of the Swedish Ground-Based GPS Network,
in ESA Conference Proceedings on Atmospheric Remote Sensing using Satellite Navigation Systems, , Matera, October 13-15, 2003, accepted for publ.

Eschelbach, C.,
The IVS-Reference Point at Onsala – High End Solution for a Real 3D-Determination,
in Proceedings of the 16 th Working Meeting on European VLBI for Geodesy and Astrometry, May 2003, Leipzig, eds. W. Schwegmann, V. Thorandt, Bundesamt für Kartographie und Geodäsie, Frankfurt/Leipzig, pp. 109-118, 2003

Gradinarsky, L., and P. Jarlemark,
Ground-Based GPS Tomography of Atmospheric Water Vapor: Analyses of Simulated and Real Data from Japan and Sweden,
Proc. International Workshop on GPS Meteorology, Tsukuba, Japan, Jan. 14-17, eds. T. Iwabuchi and Y. Shoji, Japan Meteorological Agency, 2003.

Haas, R., Johansson, K.-Å., Elgered, G., Bergstrand, S., Gradinarsky, L. P., Stoew, B., Bouma, H., and Lidberg, M.
The IVS Network Station Onsala Space Observatory.
In: N. R. Vandenberg and K. D. Baver (eds.): International VLBI Service for Geodesy and Astrometry 2002 Annual Report, NASA/TP-2003, in press, 2003.

Haas, R., Nothnagel, A., Campbell, J., and Gueguen, E.
Recent crustal movements observed with the European VLBI
network: geodetic analysis and results.
Journal of Geodynamics, 35, 391-414, 2003.

Haas, R., and Scherneck, H.-G.
The IVS Analysis Center at the Onsala Space Observatory.
In: N. R. Vandenberg and K. D. Baver (eds.): International VLBI Service for Geodesy and Astrometry 2002 Annual Report,
NASA/TP-2003, in press, 2003.

Huang, X.-Y., H. Vedel, N. Gustafsson, D. Offiler, J. A. Garcia-Moya, R. Ferritti, S. de Haan, H. Jarvinen, O. Lesne, G. Elgered, H.-P. Plag, R. Pacione, A. Rius, E. Brockmann, J. Dousa, H. van der Marel,
The TOUGH project (Targeting Optimal Use of GPS
Humidity Measurements in Meteorology)
Proc. International Workshop on GPS Meteorology, Tsukuba, Japan, Jan. 14-17, eds. T. Iwabuchi and Y. Shoji, Japan Meteorological Agency, 2003.

Jarlemark, P.O.J., and G. Elgered
Retrieval of Atmospheric Water Vapour Using a Single Frequency
Microwave Radiometer,
Int. J. Remote Sens., 24, 3821-3837 , 2003.

Khan, S. A. and H.-G. Scherneck
The M2 ocean tide loading wave in Alaska: Vertical and horizontal
displacements, modeled and observed.
Journal of Geodesy, 77, No. 3-4, 117-127, 2003.

van der Marel, H., E. Brockmann, S.D. Haan, J. Dousa, J. Johansson, G. Gendt, O. Kristiansen, O. Lesne, D. Offiler, R. Pacione, A. Rius, and F. Vespe,
COST716 Near Real-Time Demonstration Project,
Proc. International Workshop on GPS Meteorology, Tsukuba, Japan, Jan. 14-17, eds. T. Iwabuchi and Y. Shoji, Japan Meteorological Agency, 2003.

van der Marel, H., E. Brockmann, S.D. Haan, J. Dousa, G. Elgered, G. Gendt, J. Johansson, O. Kristiansen, O. Lesne, D. Offiler, R. Pacione, A. Rius, and F. Vespe,
COST-716 GPS Near Real-Time Integrated Water Vapor Network,
in ESA Conference Proceedings on Atmospheric Remote Sensing using Satellite Navigation Systems, Matera, October 13-15, 2003.

Scherneck, H.-G., J.M. Johansson, H. Koivula, T. van Dam, and J.L. Davis
Vertical crustal motion observed in the BIFROST project,
Proceedings SRCM Helsinki, 2001, J. Geodynamics, 35, 425-441, doi:10.1016/S0264-3707(03)00005-X, 2003.

2004

Milne, G.A., J.X. Mitrovica, H.-G. Scherneck, J.L. Davis, J.M. Johansson, H. Koivula, M. Vermeer
Continuous GPS measurements of postglacial adjustment in Fennoscandia: 2. Modeling results
J. Geophys. Res., 109, No. B2, doi: 10.1029/2003JB002619, 2004.