..............................................

 
 

Annual Report 2002
Chalmers / Radio- and Space Science
Space Geodesy at Onsala Space Observatory
 

1 Space Geodesy and Geodynamics

In this section we will summarize our work with geodetic Very Long Baseline Interferometry (VLBI), geodynamic
studies of the observed crustal motions in northern Europe and crustal loading. We have also used the
satellite navigation technique to study atmospheric water vapour and we are involved in the assessment of the
global navigational satellite system Galileo proposed by the European Community.

1.1 Geodetic VLBI and global reference frames

During 2002 one major activity was the participation in the CONT02 campaign and analysis of the acquired
data. Another focus was the investigation of atmospheric parameters using geodetic VLBI and complementary
techniques [1], [4]. We also continued to study the crustal deformation using the European VLBI network [11],
[12] and to secure the local geodetic ties at Onsala [15] and Ny-Ålesund [17].
1.1.1 The CONT02 VLBI campaign
Together with seven other radio telescopes spread over the whole globe, we participated in the CONT02 VLBI
campaign. This campaign of 14 days with consecutive geodetic VLBI observations aimed at a state of the art
determination of earth rotation parameters and tropospheric parameters. Parallel to the geodetic VLBI observations
we ran two microwave radiometers and a micro rain radar at the observatory in order to obtain independent
information on the atmospheric conditions during CONT02. In preparation of the geodetic data analysis, we
calculated atmospheric loading effects for all VLBI stations involved in the campaign. We also derived a model
for thermal deformation of the Onsala 20 m telescope during CONT02.
1.1.2 The IVS Pilot Project - Tropospheric Parameters
We participated in the IVS Pilot Project on Tropospheric Parameters (IVS-PPTP) as an IVS Analysis Center.
Seven Centers determined atmospheric parameters for the 12 VLBI stations involved in the IVS-R1 and IVS-R4
series. The data analyses used independent softwares and independent analysis strategies. A combination solution
for atmospheric parameters has been produced by one of the IVS Analysis Centers based on the individual
solutions.
   Figure 1 shows the distributions of zenith wet delays for the stations participating in the IVS-R1 and IVS-R4
series. The results are based on all IVS-R1 and IVS-R4 sessions from January 2002 to the end of February
2003. The large amount of water vapour in the tropical and subtropical climates (Fortaleza, Hartrao, Shanghai)
is clearly seen compared to the results from the temperate and artic climates (e.g. Wettzell, Westford,, Gilmore
Creek, Algonquin Park, Ny-Ålesund).
   An assessment of the stability of the VLBI technique to monitor the wet delay (the atmospheric water vapour
content) over long time scales continues.


Figure 1: Histograms of the zenith wet delays for the VLBI stations participating in the IVS-R1 and IVS-R4
series.

1.2 Geodynamics

1.2.1 The BIFROST GPS project
Station motion solutions based on 3000 days of GPS data in the BIFROST project (Baseline Inferences from
Fennoscandian Rebound Observations, Sealevel and Tectonics, see Johansson et al. [14]) reveal postglacial
isostatic adjustment as the dominating cause of contemporary deformation in the Fennoscandian earth crust.
Scherneck et al. [23, 24] present the recent motion solutions (see Figure 2) along with studies of robustness
of the motion parameters and with studies of climatically modulated loading effects as a potential error source.
A high geographic coherency of the observed horizontal motion was demonstrated in the Licentiate thesis of
Bergstrand [17]. In fact, we can resolve mantle viscosity parameters from the horizontal motion alone (see
Figure 3). Recent developments [24] exploit the coherency to infer crustal strain rates, which can be compared
to the seismically released strain in the area. Work has been started together with Uppsala University.
 
 

Figure 2: The map on the left shows the observed crustal motion in the BIFROST GPS network, vertical component
by gray tones and horizontal components by arrows. In the map on the right the deformation component has
been extracted. Strain rate crosses signify the two principal components. We find extension in the central uplift
area at 5-10 ×10-9 yr-1 .
 
 

Figure 3: Comparison of baseline extension between a model for the Fennoscandian glacial isostatic adjustment
(GIA) and BIFROST GPS observations in the left diagram reveals that the landuplift appears to be the dominating
cause also for length changes, other causes including systematic errors in the observations being statistically rare
or confined to within 1 mm/yr. In the right two diagrams the misfit between different GIA models and the
observations is used to determine the best fitting set of mantle viscosity parameters. Viscosities are varied in
lower mantle as shown along the abscissa and upper mantle along the ordinate, respectively. We show the mean
square error in the centre and a Fisher F-test in the right.

1.2.2 Loading problems
Deformation of the solid earth on the millimetre scale are generated under the loading pressures of the ocean
tide and the atmosphere. In cooperation with Machiel S. Bos, now at Technical University Delft, The Netherlands,
the problem was studied by Scherneck and Haas [21, 22]. During 2002 our Free Ocean Loading provider
(http://holt.oso.chalmers.se/loading) was called 690 times by users outside the oso.chalmers.se domain.

1.3 Satellite Navigation

When using the carrier phase signal for GPS navigation the positioning is made relative to a reference station. As
the distance to the reference station increase the accuracy often suffers due to the varying atmosphere. Therefore,
we have developed methods to produce estimates of the free electron content in the ionosphere and the water
vapour content in the troposphere in near-real time [13].

1.4 GPS Meteorology

During 2002 Gradinarsky defended his Ph.D. thesis [6] which assessed the use of ground-based GPS networks
is long term monitoring of the Zenith Total delay (ZTD)—and the Integrated Water Vapour (IWV). The Swedish
GPS network, which has produced data from 1993, was used to assess the stability of estimated linear trends in the
IWV [8]. The estimated trends are as expected very small. In fact the largest trend is seen at the Onsala site on
the Swedish west coast where we also have access to microwave radiometer data and nearby radiosonde launches
from the same time period. All these methods result in an estimated trend of about 0.2 mm/yr. Another interesting
research area in the thesis by Gradinarsky was the use of dense GPS networks together with tomographic methods
in order to estimate the three-dimensional structure of atmospheric water vapour. Simulations show that the
method can retrieve profiles of water vapour within certain limitations but that it requires an uncertainty in the
estimated propagation delays which cannot be accomplished today. It was, however, shown that the method will
improve significantly if more satellites were available — for example the planned European Galileo system.
A Licentiate thesis was also presented in 2002 by Bouma [3]. GPS data from 26 GPS sites in the north
of Europe were used to estimate the diurnal cycle in IWV. Typical amplitudes of the diurnal cycle were here
from 0.1 to 0.6 mm for the three summer months June, July, and August and the time period 1995–2000. These
results also show a good agreement with the climate model (version 2) of the Rossby Centre of the Swedish
Meteorological and Hydrological Institute (see Figure 4). For the other parts of the year the diurnal cycle is too
small to be detected given the much larger variations in IWV introduced by the moving weather systems.

1.5 Preparations for Galileo

It has been decided to investigate and to develop a design of a Global Navigational Satellite System (GNSS)
called Galileo by the European Community. The European Space Agency has as a consequence launched several
research studies investigating the expected quality of such an operational system. Based on our long experience
analyzing GPS data and the corresponding results a research contract was obtained in 2002 together with SP
Swedish National Testing and Research Institute and Statens Kartverk in Norway. The work includes studies of
the performance of estimating and modelling satellite orbits and clocks, as well as the ionospheric Total Electron
Content (TEC) and the water vapour in the neutral atmosphere. The project continues during 2003.
 
 

(a)

(b)

Figure 4: Estimated amplitude and phase of the diurnal component in the atmospheric water vapour content for
five consecutive summers (a) from GPS data (b) from a climate model (from [21]). Each vector represent the
result from one GPS site. The diurnal amplitude is described by the length of the vectors. The phase is illustrated
by the vector direction in a clock-wise sense and up means 0 hours (midnight) and down means 12 hours (noon).
We see that for most of the sites the maximum IWV occurs in the late afternoon.

Publications 2002

[1] Behrend, D., Haas, R., Pino, D., Gradinarsky, L.P., Keihm, S.J., Schwarz, W.,
Cucurull, L., Rius, A.,
MM5 Derived ZWDs Compared to Observational Results from VLBI, GPS and
WVR, Physics and Chemistry of the Earth 27, pp. 301-308, 2002.

[2] Bergstrand, S.,
GPS - Superficial Observations for Deeper Knowledge of the
Earth, Technical Report No. 256L, Licentiate Thesis at the School of Electrical and
Computer Engineering, Chalmers University of Technology, Göteborg, 2002.

[3] Bouma, H.,
Ground-Based GPS in Climate Research, Technical Report No.
456L, Licentiate Thesis at the School of Electrical and Computer Engineering,
Chalmers University of Technology, Göteborg, 2002.

[4] Elgered, G., D. Behrend, R. Haas, and H. Bouma,
 Atmospheric effects on the VLBI results,
 In Campbell, J., R. Haas and A. Nothnagel (eds): Measurement of Vertical Crustal
 Motion in Europe by VLBI, pp. 14-29, European Commission Research Networks,
 Training and Mobility of Researchers, Geodetic Institute, University of Bonn, 2002.

[5] Elgered, G. and B. Stoew,
 The IVS Technology Development Center at the Onsala Space Observatory.
 In Vandenberg, N.R., Baver, K.D., International VLBI Service for Geodesy and
 Astrometry 2001 Annual Report, NASA/TP-2002-210001, 2002.

[6] Gradinarsky, L.,
Sensing Atmospheric Water Vapor Using Radio Waves,
Technical Report No. 436, Doctoral Thesis at the School of Electrical and Computer
Engineering, Chalmers University of Technology, Göteborg, 2002.

[7] Gradinarsky, L.P. and P.O. Jarlemark,
 GPS tomography using the permanent network in Göteborg: Simulations.
 Proceedings of the IEEE Positioning and Navigation Symposium, pp.128-133,
 Palm Springs, USA, 2002.

[8] Gradinarsky, L.P., J.M. Johansson, H.R. Bouma, H.-G. Scherneck, and G. Elgered,
 Climate monitoring using GPS,
 Physics and Chemistry of the Earth, 27, 335-340, 2002

[9] Haas, R. K.-Å. Johansson, G. Elgered, S. Bergstrand, L.P. Gradinarsky, B. Stoew,
 H. Bouma, and M. Lidberg,
 The IVS Network Station Onsala Space Observatory.
 In Vandenberg, N.R., Baver, K.D., International VLBI Service for Geodesy and
 Astrometry 2001 Annual Report , NASA/TP-2002-210001, 2002.

[10] Haas, R., H.-G. Scherneck, M.S. Bos, J.M. Johansson, and L.P. Gradinarsky
 The IVS Special Analysis Center at the Onsala Space Observatory.
 In Vandenberg, N.R., Baver, K.D., International VLBI Service for Geodesy and
 Astrometry 2001 Annual Report, NASA/TP-2002-210001, 2002.

[11] Haas, R., Scherneck, H.-G., Gueguen, E., Nothnagel, A., and Campbell, J.,
 Large-scale strain-rates in Europe derived from observations
 in the European geodetic VLBI network,
 EGU Stephan Mueller Special Publication Series, 2, 139-152, 2002.

[12] Haas, R., and P. Tomasi,
 Results of the Geodetic VLBI Observation Program.
 In Campbell, J., R. Haas and A. Nothnagel (eds): Measurement of Vertical Crustal
 Motion in Europe by VLBI, pp. 98-102, European Commission Research Networks,
 Training and Mobility of Researchers, Geodetic Institute, University of Bonn, 2002.

[13] Jarlemark, P.O.J., J.M. Johansson, B. Stoew, G. Elgered,
 Real time GPS data processing for regional atmospheric delay derivation
 Geophys. Res. Letters, 29, DOI  10.1029/2001GL014568, 2002.

[14] Johansson, J.M., J.L. Davis, H.-G. Scherneck, G.A. Milne, M. Vermeer, J.X.
 Mitrovica, R.A. Bennett, G. Elgered, P. Elósegui, H. Koivula, M. Poutanen, B.O.
 Rönnäng, and I.I. Shapiro
 Continuous GPS measurements of postglacial adjustment in Fennoscandia, 1.
 Geodetic results,
 J. Geophys Res., 107, DOI 10.1029/2001JB000400, 2002.

[15] Lidberg, M., Haas, R., Bergstrand, S., Johansson, J., Elgered, G.,
  Local Ties Between the Space Geodetic Techniques at the Onsala Space Observatory,
  2002 General Meetings Proceedings, International VLBI Service for Geodesy and
  Astrometry, Tsukuba, Japan, NASA/CP-2002-210002, eds. N.R. Vandenberg, K.D.
  Baver, NASA, Hanover, MD, pp. 91-95, 2002

[16] Lidberg, M., J.M. Johansson, and H.-G. Scherneck,
 Re-computation of the BIFROST GPS networkand study of possible periodic effects.
 In Poutanen, M., and H. Suurmäki (eds): Proceedings of the 14'th General Meeting
 of the Nordic Geodetic Commission, pp. 66-70, Geodeettinen Laitos, Kirkkonummi,
 2002.

[17] Lidberg, M., Ch. Steinforth, R. Haas, and A. Nothnagel,
 Local tie measurements at Ny Ålensund - a status report.
 In Poutanen, M., and H. Suurmäki (eds): Proceedings of the 14'th General Meeting
 of the Nordic Geodetic Commission, pp. 94-98, Geodeettinen Laitos, Kirkkonummi,
 2002.

[18] Nothnagel, A., D. Behrend, S. Bergstrand, B. Binnenbruck, R. Haas, and Ch. Steinforth,
 Local survey ties at VLBI observatories.
 In Campbell, J., R. Haas and A. Nothnagel (eds): Measurement of Vertical Crustal
 Motion in Europe by VLBI, pp. 62-97, European Commission Research Networks,
 Training and Mobility of Researchers, Geodetic Institute, University of Bonn, 2002.

[19] Scherneck, H.-G.,
 BIFROST Project: Observing the postglacial rebound in Fennoscandia
 using continuous GPS.
 Comptes rendus 89'ieme Journées Luxembourgeoises de géodynamique, ECGS,
 Luxembourg, in press, 2002.

[20] Scherneck, H.-G.,
 IVS Analysis Working Group for Geophysical Models in VLBI software. In
 Vandenberg, N.R. and K.D. Baver (eds): 2002 General Meeting Proceedings,
 International VLBI Service for Geodesy and Astrometry, Tsukuba, Japan, pp.
 398-400, NASA/CP-2002-210002, NASA, Hanover, MD, 2002.

[21] Scherneck, H.-G., and M.S. Bos,
 Ocean tide and atmospheric loading.
 In Vandenberg, N.R. and K.D. Baver (eds): 2002 General Meeting Proceedings,
 International VLBI Service for Geodesy and Astrometry, Tsukuba, Japan, pp.
 205-214, NASA/CP-2002-210002, NASA, Hanover, MD, 2002.

[22] Scherneck, H.-G., R. Haas, and M.S. Bos,
 Station Motion Model.
 In Campbell, J., R. Haas, and A. Nothnagel (eds.) Measurement of Vertical Crustal
 Motion in Europe by VLBI, pp. 30-50, European Commission Research Networks,
 Training and Mobility of Researchers, Geodetic Institute, University of Bonn, 2002.

[23] Scherneck, H.-G., J.M. Johansson, G. Elgered, J.L. Davis, B. Jonsson,  G. Hedling,
 H. Koivula, M. Ollikainen, M. Poutanen,  M. Vermeer, J.X. Mitrovica, and G.A. Milne,
 BIFROST: Observing the Three-Dimensional Deformation of Fennoscandia.
 In: Glacial Isostatic Adjustment and the Earth System, edited by J.X. Mitrovica and
 B.L.A. Vermeersen, pp. 69-93, Geodynamics Series, Volume 29, American
 Geophysical Union, Washington, D.C., 2002.

[24] Scherneck, H.-G., J.M. Johansson, R. Haas, S. Bergstrand, M. Lidberg, and H. Koivula,
 BIFROST project: From geodetic positions to strain rates.
 In Poutanen, M., and H. Suurmäki (eds): Proceedings of the 14'th General Meeting
 of the Nordic Geodetic Commission, pp. 62-65, Geodeettinen Laitos, Kirkkonummi,
 2002.

 --
Prepared by Hans-Georg Scherneck on the basis of the section that the
Research group for Space Geodesy and Geodynamics supplied for the Annual Report 2002 of the
Chalmers Centre for Astrophysics and Space Science
Onsala, 2003-04-27.