IVS 2001 Annual Report |
![]() |
![]() |
![]() |
Rüdiger Haas, Hans-Georg Scherneck, Machiel S. Bos, Jan M. Johansson, and Lubomir P. Gradinarsky
Onsala Space Observatory (OSO)
The activities of the IVS Special Analysis Center at the Onsala Space Observatory (OSO) concentrate on a couple of particular topics that are relevant to space geodesy and geosciences. These topics can be investigated by using and developing VLBI databases and corresponding analysis programs. Routine analysis of global VLBI data in a service sense is currently not performed or planned at OSO.
Investigations concerning the elastic properties of the
earth's body have been performed by analysis of global
geodetic VLBI data and gravimetric observations
[1].
The work concentrated on observations performed
at the Geodetic Observatory Ny-Ålesund and
the tidal harmonic (13.66 day period)
because the long-period tides reach their maxima
in polar regions and they are
more sensitive to mantle inelasticities than diurnal
earth tides.
The analysis of 14 months of continuous observations
with the superconducting gravimeter at Ny-Ålesund
allows the determination of gravimetric factors for
several tidal harmonics.
However, the gravimetric factor obtained for the
tide still does not allow us to clearly distinguish
between elastic and inelastic
body tide models since the uncertainty of the determined
gravimetric factor is still too large.
The analysis of a data set of more than 200 global
VLBI data bases involving Ny-Ålesund so far only
concentrated on the question of whether the
tide can be
detected directly from time series of VLBI station
positions.
Our study shows that the
tide could be identified successfully in
the spectra of the topocentric up-component of
Ny-Ålesund when this tide was not modelled in the
apriori solid earth tide model.
Based on this promising first step further
investigations to determine directly the
corresponding Love number are ongoing.
Ocean tide loading is investigated at OSO both by
theoretical modelling and by empirical determination
of ocean tide loading effects [2].
Ocean tide loading coefficients based on recent ocean tide models
have been calculated and made available for a global set of VLBI
stations (http://www.oso.chalmers.se/hgs/README.html).
An automated ocean tide loading provider has been developed
by Hans-Georg Scherneck and Machiel Bos during 2001.
It is available under
http://www.oso.chalmers.se/loading and
offers the calculation of ocean tide loading coefficients
based on 11 different ocean tide models for user-defined
input stations.
From analysis of the VLBI data observed in the European VLBI
network we can conclude that the application of the more
recent loading models based on finite element ocean tide models
and assimilation of satellite altimetry data results in
smaller values for the least-squares analysis
than when using an ocean tide loading model
based on an older ocean tide model that had been
developed in the 80s [3].
Global convolution of atmopheric pressure fields is used
to calculate time series of atmospheric loading predictions.
They are available for most of the VLBI databases since 1990
http://www.oso.chalmers.se/hgs/apload/apload.html.
Crustal movements in Europe have been derived based on 11 years of purely European geodetic VLBI observations [3]. Figure 1 shows the weighted root mean square values (wrms) of the baseline measurements in the European VLBI network as a function of baseline length. Baselines that involve Simeiz and/or Yebes are excluded because of poor performance.
![]() |
The results for topocentric station motions with respect to Wettzell have been used for geological interpretation [4] and to determine the European large-scale strain-rate field [5].
The usage of collocated space geodetic and remote sensing techniques
for atmospheric studies has been continued
[6], [7].
Results for atmospheric parameters derived from
several collocated techniques (VLBI, GPS, WVR)
at the three sites Onsala, Wettzell and Madrid
have been compared to results from a numerical
weather model for several days in 1999.
Each of the three sites of the European geodetic VLBI
network is located in a different climatological regime.
Correlation coefficients in the range of 75-95
are found for the zenith wet delays
of the different and independent techniques
[8].
While the biases of the GPS and WVR results with respect to the numerical
weather model appear to be station dependent, such a station
dependence does not appear to exist for the VLBI biases.
VLBI seems to provide a useful calibration data set
for climate studies and numerical weather models.
After having participated already in the First IVS Analysis Pilot Project in 2000, the IVS Special Analysis Center at OSO also participated in the Second IVS Analysis Pilot Project in 2001. Earth orientation parameters (EOP) obtained from the 104 NEOS-A sessions observed in 1999 and 2000 and the corresponding atmospheric parameters have been submitted to the IVS analysis coordinator. Figure 2 shows the EOP (left side) and the corresponding standard deviations (right side).
![]() |
The IVS Special Analysis Center at the Onsala Space Observatory will continue to work on specific topics that are relevant for space geodesy and geosciences. This includes in particular solid earth tides, loading effects due to ocean and atmosphere, earth rotation, crustal motion and atmospheric properties.
A special focus for the future will be the investigation of combination strategies for VLBI and GPS in particular to derive a more detailed picture of the strain-rate field in Europe and to investigate changes in absolute sea level. The geophysical interpretation of the derived results will be of major concern.
The study of loading phenomena due to oceanic, atmospheric and other enviromental influences will be continued especially in connection with earth rotation studies and reference frame investigations. On a longer time scale, a contribution to IVS by EOP solutions and reference frame solutions is also planned.
The atmopsheric studies will mainly focus on the application of space geodesy for climatological studies. Long time records of atmospheric parameters derived from VLBI and GPS appear to be important sources of information.
![]() |
![]() |
![]() |
IVS 2001 Annual Report |