Geodetic activities in Finland 2006 International Association of Geodesy (IAG)

Report for the IUGG National Committee,

Compiled by Markku Poutanen Finnish Geodetic Institute (FGI)

1 Finnish Geodetic Institute 1.1 Reference frames and the permanent GPS network, FinnRef The Finnish Geodetic Institute hosts the permanent GPS network FinnRef, which consists of 13 permanent GPS stations. The network is the backbone of the Finnish realisation of the European reference system ETRS89. The National realisation of the reference frame is called EUREF-FIN. Connections to the neighboring countries and international networks, and maintaining of the reference frame are the responsibilities of the FGI. Four stations in the FinnRef network (Metsähovi, Vaasa, Joensuu, Sodankylä) belong to the EUREF permanent GNSS network (EPN), and one station (Metsähovi) belongs to the network of the International GNSS Service (IGS) of the IAG. Through these stations FinnRef creates a connection to the global reference frames and the stations are used for maintaining global reference frames and global geodetic studies. The data recorded in the EPN stations are transferred automatically hourly to the EPN regional data centres in Austria and Germany. The data are also transferred to the Onsala Space Observatory in Sweden for the BIFROST project. The FinnRef stations are also used for local studies on crustal movements as well as a reference for local and national GPS measurements. The absolute gravity observations were made at six GPS stations, viz. in Metsähovi, Vaasa, Joensuu, Sodankylä, Kuusamo and Kevo with FG5 gravimeter. Related to the IAGs project GGOS (Global Geodetic Observing System), the Nordic plan, NGOS (Nordic Geodetic Observing System) was continued as a task force of the Nordic Geodetic Commission. Markku Poutanen was the chairman of the task force, and a member of the GGOS steering committee. GGOS will be the most important geodetic effort in the coming years, and in NGOS the development of GGOS will be followed. Via GGOS geodetic data will be made available to the great public and researchers in a well controlled and uniform way. The Finnish Geodetic Institute (FGI) has participated in national committees and working groups in order to advance the usage and help in practical questions of the new reference frame, EUREF-FIN, in Finland. Also, several lectures and presentations were given.

1.2. Height systems The field work of the Third Precise Levelling of Finland, started in 1978, was completed in 2004. A total of more than 9000 km of double-run lines were measured, comprising more than 6000 benchmarks. Data were analysed, and a common Nordic adjustment was made on the network around the Baltic Sea to tie the national networks firmly into the European network. Based on the results of the adjustment, the new national height system N2000 was made following the guidelines of the European EVRS2000, and those agreed in the Nordic Geodetic Commission. N2000 will coincide with the new Swedish height system better than 2 mm at the border of Finland and Sweden in the valley of Tornio River.

1 The subcommission EUREF started in 2004 the project, which is called EUVN_DA (European Unified Vertical Network Densification Action). The purpose of the project is to densify the GPS/Levelling network in Europe so that the distance between the neighbouring stations will be less than 100 km. The minimum GPS observation time at a point should be at least 24 hours, and the point should be connected by precise levelling to the closest nodal point of the UELN network. A total of 30 GPS/levelling points were measured in Finland in 2005. The results were presented to the EUREF commission in the annual meeting in Riga and published in the series of the FGI. One connection to the Russian border was levelled in 2006 thus completing the project of measuring connections over the Finnish-Russian border. Joint publication of the project was published in the series of the FGI.

1.3. Gravimetric works 1.3.1 Absolute gravimetry In December-January 2005/2006, FGI performed absolute gravity measurements at the Finnish Antarctic base Aboa with the FG5-221. Previously, FGI had measured at Aboa in 1994, 2001 and 2004. Repeated measurements are used for geodynamical studies. Single occupations provide reference values for gravity surveys. Repeated measurements were made also at the South-African Sanae IV, and the Russian Station Novolazarevskaya. The Nordic Absolute Gravity Project was launched in 2003. It aims at producing a time series of absolute gravity measurements at about 20 Nordic sites. The time series will be compared with estimates of regional mantle inflow (due to the Fennoscandian postglacial rebound) obtained from the ongoing mission of the GRACE gravity satellite. As a by- product, a highly accurate gravity reference network with estimates of gravity change rates will be produced. The absolute measurements are performed by IfE (Institut für Erdmessung, University of Hannover), Norwegian University of Life Sciences, BKG (Bundesamt für Kartografie und Geodäsie, Frankfurt), and FGI, in cooperation with the Danish Space Center, the Norwegian Mapping Authority, and Lantmäteriet (Sweden). In 2006 FGI observed at 7 sites. The project is coordinated by the Working Group for Geodynamics of the Nordic Geodetic Commission (NKG), as a part of the Nordic Geodetic Observing System (NGOS) of the NKG. A comparison between IfE (Institute für Erdmessung, University of Hannover, Germany) and FGI gravimeters took place in Metsähovi. At Metsähovi the gravity is measured regularly, and fhe absolute gravity has been observed in Metsähovi more than 80 times since 1988.

1.3.2 Relative gravimetry Studies on the Keurusselkä impact structure in Central-West Finland were continued by detailed analyse of the 2005 gravity survey. Measured four gravity profiles (NS, EW, NE- SW,NW-SE) and densification of the gravity net of the Finnish Geodetic Institute reveal a Bouguer anomaly minimum in the impact area and there exists a small local anomaly maximum in the shatter cone area. The size of impact structure is still unknown and new gravity measurements are needed for investigation of the structure details. The studies on the Keurusselkä impact structure continue also by comparing gravity anomaly result with other geophysical investigations (FIRE-seismic, magnetic, petrophysical, topography etc.) in cooperation with the Solid Earth Geophysics section of the Department of Physical Sciences in the University of Helsinki.

2 1.3.3 Superconducting gravimetry The superconducting gravimeter GWR T020 at Metsähovi has been operational since August 1994. It participates in the GGP (Global geodynamics project), where 20 SG’s are deployed worldwide. In addition to the gravity data, the recordings consist of air pressure, groundwater level and precipitation. Studies of gravity data comprise the gravity spectrum from microseism to Chandlerian period. The research work has been focused on loading effects from air pressure field and the Baltic Sea. Use of the superconducting gravimeter for hydrological studies is investigated in cooperation with the Helsinki University of Technology (Department of Rock Engineering), Finnish Environment Institute, and the Geological Survey of Finland. Modelling of the Influence of Atmospheric Masses and Baltic Sea Level on Gravity in cooperation with the Finnish Meteorological Institute and the Finnish Institute of Marine Research continued. The detailed HIRLAM (High Resolution Limited Area Model) air pressure grid gives gravity correction models that during special events like the passage of strong anticyclones differ up to 10 nm s –2 from simple regression models. This improves the detection and modelling of signals correlated with air pressure, e.g. Baltic Sea level variations. Hydrological loading effects were calculated using both the high accurate model for Finland (Watershed Simulation and forecasting System, WSFS, by the Finnish Environment Institute) and the Climate Prediction Center global soil moisture data set (CPC). Results were compared and evaluated with SG and local permanent GPS observations. FGI participated in global and European studies where the variation in surface gravity observed point wise with the SGs is correlated with variation in regional gravity observed with the satellites CHAMP and GRACE, and with the variation in regional gravity predicted from global models of terrestrial water storage. One Doctoral Thesis on the topic was completed in 2006.

1.3.4 Satellite gravimetry GRACE time series were analysed and compared with time series from the superconducting gravimeter in Metsähovi. Furthermore, surface mass variations were estimated from the GRACE time series and they were compared with variations in global watershed models and the Finnish Watershed Simulation and Forecasting System of the Finnish Environment Institute. Good correlations were found.

1.3.5 Geoid models Work was done to calculate two new geoid models for Finland based on the new Nordic geoid model, NKG2004, and a new network of GPS and levelling data. The first model is for use with the old height system and the second with the new height system. Both models will be published in 2007 when the new height system for Finland is introduced.

1.4. The Metsähovi Research station The Metsähovi research station was founded in 1978 and it has through the years become an essential part of the activities of the FGI. Currently, it is globally one of the most versatile space geodetic station. The instrumentation covers the satellite laser ranging (SLR), geodetic VLBI, GPS and GLONASS receivers, DORIS beacon, superconducting gravimeter, seismometer and the fundamental absolute gravity point. The Metsähovi Satellite Laser Ranging (SLR) was discontinued during the year 2006.. Preparations to renew the laser system were started, and a new laser was ordered. As a co-operation project with the Metsähovi Radio Research Station of the Helsinki University of Technology, geodetic VLBI observations were continued. Eight campaigns

3 were made in 2006, as a part of the IVS (International VLBI Service) network and the European geodynamics project. The Metsähovi GPS station continued as a part of the Finnish permanent GPS network, FinnRef. Data were submitted to the European permanent GPS network computation as well as IGS network. Also, data from Javad/Legacy GPS/GLONASS receiver were submitted to the GLONASS data center for the IAG IGLOS (International Association of Geodesy GLONASS project). Based on an agreement with NASA, a GPS receiver of JPL was installed in 2006, submitting real-time 1 s data in the NASA network. The French Doris beacon, operated by CNES, continued its operation.

1.5. Deformation studies, postglacial rebound Investigation of local crustal motions contained in a contract with Posiva Oy was continued on three sites. The local networks at Olkiluoto, Kivetty and Romuvaara were measured with GPS. Olkiluoto which is now selected as the nuclear waste deposit site, is measured twice a year, two other sites, earlier as a candidate sites for the waste deposit, serve now as a reference network, and they are measured once a year. Ten-year time series allow better than 0.5 mm/yr tracking for 3D-crustal movements. This far, no statistically significant movements have been discovered. A larger network, as a part of Geo-Satakunta project was measured with GPS three times during the year 2006. Olkiluoto network is a subnet of this larger network. Other participants in Geo-Satakunta are the Geological Survey of Finland, and Cities of Pori and Rauma. The project is partly funded by EU, and its goal is to study geology and geophysics of the area, including crustal movements. 13 stations of FinnRef permanent GPS network collect continuous dual-frequency GPS data. Most of the stations have been active since 1996 offering a possibility for 10-year long time series. The distances between the stations are 100-200 km. A more dense set of measurements was done in 1996-1997 when FGI created a EUREF-FIN coordinate reference in Finland by measuring 100 old 1st order triangulation points with GPS. This measurement was repeated in 2006 (EUREF-RE campaign) offering us a possibility to study the intra-plate deformations in a more detailed way. Studies on temporal variations on the time series of the Finnish permanent GPS stations FinnRef were continued. Additional information using data of Metsähovi superconducting gravimeter, and ocean and atmospheric loading were used. This was a joint project with the Finnish Meteorological Institute, and partly funded by the Finnish Agency for Technology and Innovation, TEKES. The goal is to study both crustal deformations and atmospheric effects on GPS signal. One of the applications could be the use of GPS signal as a part of operational weather forecast in the future. Significant improvement in accuracy was achieved by using the weather forecast model and computing the delay in the GPS signal due to the troposhpehe.

1.6. Antarctic project Since 1989 FGI has participated on research in Antarctica. The field expeditions have measured the geodetic reference net for the mapping of the surroundings of the Finnish Antarctic base Aboa, and measured a regional gravity network. One field of study is the rebound using repeated absolute gravity determinations at Aboa. Repeated gravity measurements are used for geodynamical studies. Single occupations provide much-needed reference values for gravity surveys. A permanent GPS station of the FGI at the Finnish Antarctic base Aboa was put in operation in year 2003. Since that, continuous time series have been collected. At the end of

4 the year 2006, four years of data already existed. Data were collected during the field expedition 2005/2006 and 2006/2007. During the field expedition Finnarp2005/2006, a remeasurement of the absolute gravity was made at Aboa. Using data from repeated absolute gravity measurements, GPS and local kinematic GPS determination of snow/ice changes, allows us later to estimate the direction of the vertical crustal motion and the behaviour of the surrounding glacier. During the expedition absolute gravimetry was measured at three points, Aboa, Sanae IV (South Africa) and Novolazarevskaya (Russia). FGI participated in the evaluation of Finnish Antarctic Research, organised by the Academy of Finland.

1.7. National Standards Laboratory The FGI is a National Standards Laboratory (NSL) of length and acceleration of free fall, as prescribed in the law (581/2000). Since 2002 the Finnish Geodetic Institute has been in the Mutual Recognition Arrangement (MRA) of national measurement standards and of calibration and measurement certificates issued by national metrology institutes. The FGI has implemented a quality management system according to the ISO17025 standard. Computation of the interference measurements at the Nummela Standard Baseline in autumn 2005 was completed. The results show good accuracy, repeatability and stability. The baseline has been 60 years a world-class measurement standard in geodetic length metrology. In autumn 2006 the FGI participated in the Asia-Pacific Metrology Programme comparison for pilot study on calibration of electronic distance measurement equipment. Obviously this was the first official international metrological comparison of that kind in the world. In this comparison the FGI transferred the scale of the Nummela Standard Baseline to a baseline in South Korea using a precise measurement instrument of the Helsinki University of Technology as a transfer standard. Comparisons with measurements utilizing other methods for traceability are in progress. The vertical laser rod comparator has been used to calibrate the rods of the FGI used in precise levelling. In addition, invar rods and digital levels used in Baltic and Nordic countries have been calibrated. The FGI has the FG5 absolute gravimeter no. 221 as the primary standard for the acceleration of free fall. The traceability is based on a laser interferometer and a rubidium standard. The primary point in Metsähovi has been observed on a regular basis.

1.8. Virolahti RIMS station The EGNOS (European Geostationary Navigation Overlay Service) RIMS (Ranging and Integrity Monitoring Station) station in Virolahti has been deployed during 2004. It has been established in a co-operation with the European Space Agency (ESA). The station continued in full operation. Observations are sent to the EGNOS MCC (Mission Control Centre) in Germany in real-time via the EGNOS wide area network.

2. Helsinki University of Technology (Reported by Martin Vermeer)

The First Symposium of the International Gravity Field Service (IGFS2006) took place in Istanbul, Turkey, Aug 28 - Sept 1, 2006. Prof. Martin Vermeer acted as convener of Session 10: Geodynamics and gravity change. Peer-reviewed Proceedings are in preparation. Prof.

5 Vermeer chairs the IAG Sub-commission 2.2: Spatial and Temporal Gravity Field and Geoid Modelling. Oct 27, Prof. Vermeer acted as opponent of Ramin Kiamehr, on the doctoral dissertation "Precise Gravimetric Geoid Model of Iran Based on GRACE and SRTM Data and the Least- Squares Modification of Stokes' Formula with Some Geodynamic Interpretations". Royal Institute of Technology, Stockholm, Sweden. The Nordic Journal of Surveying and Real Estate Research (NJSR), editor-in-chief Martin Vermeer, published one issue (Volume 2 No. 1) with four articles, two on geodetic subjects. During 2006, three diploma theses and one licentiate thesis appeared on geodetic subjects.

3. National Land Survey of Finland (Reported by Marko Ollikainen)

The densification of the National networks was continued. The densification of the EUREF- FIN network, originally measured by the Finnish Geodetic Institute (FGI), was continued by measuring lower order points. Some measurements were still done in the kkj grid coordinate system, which is the previous coordinate reference system in Finland. The densification of the levelling network and re-levellings of some old levelling lines were continued. The new height system for Finland (N2000) was determined by FGI. Preparations to adjust National Land Survey’s levelling lines into the new height system have been done. The recommendations for public administration concerning the new height system and its utilization have been prepared in co-operation with FGI.

4. Publications

Seven peer-reviewed publications and 17 other scientific publications appeared in 2006.

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