There is currently a great need to compile a uniform gravity grid of the Arctic region, for use in both geophysics/geology and geodesy/orbit determination. Recent advances in data collection technology, notably the advent of airborne gravimetry, the development of satellite altimetry over ice-covered regions, and availability of gravity data from scientific cruises with nuclear submarines, have meant that a large part of the Arctic is covered by substantial, accessible gravity field information.
The ArcGP will provide a detailed insight into the tectonics of the region, and allowing for the first time an accurate geoid model to be established. Recent presentations make it clear that monumental efforts have been made by Russia in mapping major parts of the gravity field of the Arctic Ocean, and make the formation of the ArcGP timely. The establishment of a freely available uniform gravity grid of the Arctic follows ongoing activities to develop an Arctic bathymetric map and database under the auspices of the International Hydrographic Office (IHO).
The Arctic Gravity Project (AGP) is a new international effort dedicated to the compilation of a public-domain gravity grid of the Arctic gravity field north of 64° N. The focus of the gravity grid will be the Arctic Ocean, Greenland, and the continental margins of the Asian and North American continents. The initiative for the project was taken after two international meetings in 1998 ("Airborne Gravity Measurements and the Polar Gravity Field", Greenland, June 1999, and the "International Conference on Arctic Margins (ICAM-III)" held in Celle, Germany, October 1999). The project proposal was inspired by presentations of Russian scientists, and by the success of the ongoing IHO project on Arctic Bathymetry. Ron McNabb, Canada, and B. Coakley, USA, were originally proposing a formal working group on gravity, for which the undersigned was subsequently proposed as chairman.
The primary interest is the compilation of state-of-the-art detailed free-air and Bouguer anomaly grids that will be made available to the general public in the year 2001. Additional tasks for the Arctic Gravity Project working group is to compare and calibrate different gravity sources, e.g. comparison of airborne, satellite, surface and submarine data, and the computation of an arctic-wide geoid model.
At the ICAM-III meeting National Imagery and Mapping Agency (NIMA) offered the future ArcGP to assist in the compilation of the final gravity grid products, using the extensive personnel and computer resources available at NIMA for this kind of work, and to release all data for the compilation of the grid product (the original data will not be made available, only the grids), including recent data acquired by the Naval Research Laboratory airborne gravity programmes plus other surface gravity data from its Point Gravity Anomaly file which contains over 35 million data values.
The target date for final 5 x 10 free-air and bouguer gravity grids to be released to BGI and the general public is December 2000 with preliminary grids released in 1999 to AGP Working Group Members. It is also planned to publish a CD-ROM.
Activities up to July 1999
Following the call for participation in the ArcGP groups activities, positive responses were obtained from all circum-arctic countries and some other major major data-active countries, cf. the list of members below. It was also agreed that the goal of the project is to produce a 5 grid (10 in longitude) covering the area north of 64N, with the exception of Iceland, where 62 N will be used as southern limit.
The National Imagery and Mapping Agency (NIMA) has designated an ftp box for data collection, and has set up a ArcGP web site (http://www.nima.mil/GandG/arctic.htm).
The International Association of Geodesy has approved the ArcGP as a "Special Study Group" belonging to Section III - Gravity Field Determination. An application has also been made to the International Arctic Science Committee (IASC) the have ArcGP recognized as an official IASC project.
Numerous countries and investigators have allready contributed significant data sets, which has allowed a first-cut compilation of available data, to be presented in the IUGG symposium on "Polar Geophysics".
The following data sources have been contributed as of July 1999, and used for the initial compilations of data, to be presented at IUGG. Some of these providers have provided national data base extracts including commercial data. We thank all the data providers who have allready committed data for the project at this early stage.
National Land Survey (LMV) - Sweden Swedish point gravity data (2.5 resolution)
Geodettinen Laitos Finland Finnish point gravity data (do)
Statens Kartverk (SK) Norway Svalbard/Norway available land and marine gravity data
Orkustofnum - Iceland Icelandic land and marine gravity data
National Survey and Cadastre -Denmark Greenland land, marine and airborne gravity data
Tsniigaik - Russia European Russia 10 gravity grid
NIMA USA North American point and NRL airborne data
B. Coakley Lamont/USA SCICEX Arctic Ocean submarine gravity
Geomatics Canada (EMR) - Canada Canadian data, incl. new Ellesmere Island data
Alfred Wegener Institute - Germany Fram Strait/Greenland airborne and marine gravity data
Bureau Gravimetrique - France Marine gravity from satellite altimetry over sea-ice
We hope in the future especially to expand this list with more Russian data, more oil company data (e.g., north of Alaska) and to incorporate data from ongoing 1999 field activies by airborne and submarine surveys.