Geodetic Oberserving System
Permanent GPS Stations
Research in the field of geodetic infrastructure is carried out with the aim of maintaining and developing geodetic reference systems and reference frames so that the national implementation as a basis for the spatial infrastructure, including surveying and mapping, meets its users' requirements for accuracy and integrity at all times.
An important task is to introduce and define new international standards such as the ITRFs at the national defining points and stations. It is thus our task to facilitate the transformation towards new standards in line with the national official reference frame in ETRS89 called EUREF89.
Our main challenge is to establish a consistent link between the global navigation satellite systems (GNSSs) and the national reference frames so that these GNSSs can be fully utilized in positioning and navigation. An important issue in this context is to define a velocity field that can compensate for continental drift and crustal deformations.
Another important challenge is to develop an accurate, long-term, stable reference frame, which is needed in global monitoring to detect changes in e.g. sea level and ice caps. The development of such accurate stable reference frames will also facilitate the use of GNSSs in monitoring deformations in big structures, bridges, harbours, oil rigs etc.
Research in the field of positioning is being carried out with the aim of developing new positioning techniques that can be used by society for surveying and navigation purposes. Particular efforts are being made in research on the use of global navigation satellite systems (GNSSs - mainly GPS) for both static and kinematic positioning and for the determination of reference coordinates. The classical method of levelling is still used for accurate height determination.
Analysis of time series from permanent GPS stations helps to attain accurate coordinate determinations and to extract information about crustal movements. Furthermore, it also makes it possible to monitor the integrity of the satellite systems and detect problems. Issues relating to the stability of the global reference frames are currently being studied to enhance the accuracy of the coordinates, which will facilitate new GNSS applications. A major effort is also being put into the detection of ice load changes in Greenland based on permanent GPS combined with campaign measurements.
The use of kinematic positioning in real time using GNSS has huge potential in navigation and could be used in for a variety of applications in surveying, traffic, farming, and location-based services. Our research aims to enhance kinematic GNSS, which will facilitate these developments and to prepare for GALILEO so that we obtain the full benefits of this investment.
Our research in Earth observation aims to establish knowledge about new mapping techniques and other Earth observation tasks in order that society can take full advantage of these new technologies. We mainly focus on applications stemming from new Earth observation satellites and the development of data processing and analysis methods related to the mapping of heights and height changes of land, ocean and ice surfaces. For urban mapping, we are developing automatic change detection methods that will enhance the use of remote sensing data in topographic mapping.
One of our core activities is the mapping of marine geodetic quantities based on satellite altimetry. The NSI global marine gravity field, global mean sea surface and ocean tide models are widely-known, widely-used products stemming from this activity. Including satellite gravity from GRACE and GOCE, we are developing methods to enhance the determination of the mean dynamic topography and improve the modeling of ocean currents and transports.
An important challenge is to develop methods for utilizing Earth observation satellites in global change monitoring and observations of the impact of the varying climate. We are helping to develop techniques for the global monitoring of sea level changes and to develop reference surfaces for ocean modeling and forecasting for the European Global Monitoring for Environment and Security (GMES). A pioneering field is to use satellite gravity changes from GRACE to detect changes in ground water storages.
Geodetic observations are needed to carry out geodetic tasks such as establishing reference frames. Many tasks require standardized globally distributed data that have been quality checked. Furthermore, collocated data of various kinds (e.g. position and sea level or position and gravity) may be required in research. Hence, international collaboration and coordination are needed to develop the observing system, so that the data requirements can be fulfilled. As part of our national responsibility, we supply data from our national territory - Greenland in particular.
One of our core activities is our participation in the international activities to develop a global network of permanent GPS stations; we are developing a network of permanent GPS stations in Greenland to help to meet these international requirements and standards. We also participate in the international development of a network of sea level recording stations, and we are developing a network of such stations in Greenland. These developments are associated with instrumentation and communication and also complement the instrumentation of other geodetic techniques that may be requested.
We contribute to the development of the Global Geodetic Observing System (GGOS) and its regional implementation and densification, the Nordic Geodetic Observing System (NGOS).
As part of our national responsibility to supply data from our national territory - Greenland in particular – to the international community we operate a number of permanent GPS stations in Greenland. The data are sent to the International GNSS Service and similar European centers, where data are made available to other users and used for monitoring and improving the performance of the GNSS. Two stations are so-called global stations and used for the determination of new international reference frames.
In Thule we host a DORIS beacon. DORIS is a global satellite tracking system mainly used for orbit determination for Earth observation satellites.
We also operate sea level recorders at specific sites in Greenland – collocated with GPS – to acquire information on sea level to support research and calibration of spaceborne instruments. These stations are operated according to international standards adopted by GLOSS and the European Sea-level Service (ESEAS). Data are made available through ESEAS and the Permanent Service for Mean Sea Level (PSMSL).
Head of division Per Knudsen.