Gravitations-kort over jorden. (Billede: NASA)

Geodesy and Geodynamics

The divisions main research areas are: Geodetic infrastructure. Development of techniques for surveying and mapping. Refinement of space-based Earth Observation techniques. Mapping the cryosphere. Modelling the Earth's gravity field. 

The division is participating in a wide array of research projects and scientific activities ranging from improving GNSS positioning systems to climate related ice and sea monitoring and modelling.

The division work also work with mapping and monitoring of the cryosphere, determining and modelling the thw Earth's gravity field in support of global and regional geodynamics, geoid determination and national gravity networks.

We conduct Earth observation research and projects - airborne, satellite and on the ground - in geodesy and geodynamics. We work with ESA, EU and other national and international organizations.  We manage DTU Space's role in the Danish Continental Shelf Project through provision of geophysical data and geodetic know-how.

 

Geodetic Infrastructure:

 

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.

 

GNSS Positioning:

 

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.

 

Earth Observation

 

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 Oberserving System:

 

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).


Permanent GPS Stations:

 

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).

 

Gravity Field Mapping:

 

Since 1996 we have carried out extensive airborne gravity campaigns for regional gravity field determination, especially in the Arctic (Greenland, Svalbard and Canada regions), as well as dedicated projects to map the marine geoid for ocean dynamic topography estimation (North Atlantic, Baltic Sea, Azores, Greece and Australia) and minor demonstration projects for oil exploration (Italy and Svalbard). Over the years the system has been installed in a large number of different aircraft (Twin-Otter, Antonov-38, Cessna Caravan, Fokker-27, Casa-212 and others), highlighting the versatility of airborne gravity.

Major projects include nationwide geoid and regional gravity surveys of Malaysia (2002-3), Mongolia (2004-5), and Ethiopia (2006-7). Our airborne gravity system is based on a Lacoste and Romberg ´S`-type marine gravimeter, modified for airborne use by ZLS Corporation, and augmented by a medium-grade Honeywell inertial navigation system and numerous geodetic GPS receivers. During good flight conditions the system gives an accuracy of 1.5-2 mgal at 5-6 km resolution. 

 

The Continental Shelf:

 

On 29 April 2003 the Danish Parliament decided to ratify the United Nations Convention on the Law of the Sea (UNCLOS). This decision was later also endorsed by the Parliaments of the Faroe Islands and Greenland. Denmark ratified UNCLOS on 16 November 2004. Denmark had 10 years from this date to put forward any claims to extend the outer limits of its continental shelf beyond 200 nautical miles. Five potential claim areas have been identified off the Faroe Islands and Greenland, potentially including the North Pole.

In order to provide a database of the necessary information, the Danish Continental Shelf Project was launched by the Ministry for Science, Technology and Innovation in co-operation with the Faroese and Greenland home rule governments. The project is a co-operation between various institutions in Denmark, the Faroe Islands and Greenland. The main tasks of the Continental Shelf Project are to identify potential claim areas and to acquire, interpret and document the necessary data for a submission to the United Nations. We support the project by ensuring accurate GPS-measurements and intepreting data from satellites measuring gravity and ice cover.

Contact

Per Knudsen
Professor, Head of Geodesy
DTU Space
+4545 25 97 18

Contact

René Forsberg
Professor, Head of Geodynamics
DTU Space
+4545 25 97 19