Minutes of 3rd working group meeting, Ottawa, May 18, 2001



International Association of Geodesy

International Gravity and Geoid Commission

Arctic Gravity Project

Minutes of 3rd working group meeting, Ottawa, May 18, 2001


The meeting was held at Natural Resources, Canada, upon invitation of the Geodetic Survey Division, National Resources Canada. The meeting was split in two parts:

A technical session with presentations of new developments in national or major projects, and an Arctic Gravity Project (ArcGP) business meeting where the status and conclusion of ArcGP was discussed.

 

Background of ArcGP

ArcGP is a working group under the International Association of Geodesy, International Gravity and Geoid Commission. The WG has the goal to compile a uniform gravity grid of the Arctic region (north of 64° N), with the aim to

ArcGP was initiated in 1998, and earlier WG meetings have been held in Birmingham (1999) and St. Petersburg (2000). All major countries and research institutions collecting data in the Arctic region have at present to a varying degree contributed data for the project.

 

Summary of the technical session û "Arctic Gravity and Geophysics"

The session was part of the Canadian Geophysical Union annual meeting. The following papers were presented:

R. Forsberg (KMS, Denmark; chairman of ArcGP): Arctic Gravity Project, status and background. Gave an overview of the project history and current status. Also honored the late Sergei S. Maschenkov (VNIIO), who passed away this winter, for his influential role in the establishment and cooperation of ArcGP.

A. Zayonchek, S. Maschenkov, V. Glebovsky, S. A. Paukky, A. A. Chernyh (VNIIO, Russia): Gravity data applications in Russian geophysical projects for the Arctic studies. Outlined, a.o., the ongoing Russian geophysical mapping program in scale 1:1 mio, and special works in geotransects 100 km wide, with data originating from National Resource Ministry, VNIIO and PMGE.

B. Coakley (Tulane Univ., USA): Gravity and bathymetry of the SCICEX submarine program. Outlined highlights of the 1999 Scicex cruise, such as the detection of active lava flows on the Gakkel Ridge, and new data from Lomonossov Ridge, indicating an ice cap existed there during last glacial maximum. Described processing status of 1999 gravity data.

V. Childers, J. Brozena (Naval Research Lab., USA): NRL long-range airborne Arctic geophysics program û an update. NRL have covered major parts of the central Arctic Ocean with long-range aerogravity, at accuracy of 2 mGal and resolution 15 km. No new arctic data have been collected since St. Petersburg meeting.

T. Boebel (Alfred Wegener Institute, Germany): Advanced tectonic model of Svalbard, northern Fram Strait, and eastern northern Greenland. Outlined the AWI aerogeophysical survey program in the region 1997-2000, and its tectonic implications, e.g. for understanding the Lena Trough.

N. Khlupin, V. Leonov, S. Mandrikov (Polar Marine Geosurvey Expeditions, Russia): Russian airborne gravimetry investigations of the Kara-Barents shelf 1993-2000. Updated presentation of Russian aerogeophysical investigations, including hardware descriptions. More than 800 hr have been flown at 5-10 km line spacing, with accuracy of 5 mGal at 4 min filtering. Data are used in compilation of 1:1 mio geophysical maps.

R. Forsberg, A. Olesen, K. Keller (KMS, Denmark): Greenland shelf region airborne gravity program 1998-2001. Described recent results of KMS "low and slow" Twin-Otter aerogravity flights. All Greenland coastal regions are now covered, in addition to Fram Strait. Accuracy of measurements 2 mGal.

D. Solheim, A. Gidskehaug (Norway): Svalbard and Fram Strait airborne gravity activities 1998-2001. Described airborne gravity surveys around the Svalbard archipelago and surrounding seas, carried out in close cooperation with KMS. Presented some problems with downward continuation over land areas with glaciers. Some 1999 data still to be processed.

G. Deminov, A. Mayorov (Tsniigaik, Russia): The problem of world height system establishment by gravity and GPS data û example of Arctic geoid. Stressed the need for computing quasigeoid to link vertical systems and establish a unified global vertical datum. ArcGP geoid aspects very important. Outlined ongoing Russian program with GPS on benchmarks.

M. Veronneau, J. Halpenny (NRCan, Canada): Canadian arctic land and airborne gravity data projects. Land and airborne activities (PMAP 1998 project) were outlined. No new data acquired since previous ArcGP mtg. Some areas still without data (especially Foxe Basin), target for future airborne surveys.

NGA, R. Forsberg: Processing of ArcGP gravity data and some intercomparisons. Gave data status of data submitted so far to ArcGP computing center at NGA, with some comparisons of the problems of data merging of data with different resolution, and presented overview gravity map. Current data coverage percentage in terms of different sources:


Protocol of the ArcGP business meeting

Afternoon was reserved for discussions on the project, reaffirming the basic principles of data release, grid preparation, remaining problems with data, potential new data, and publication policy. The meeting had simultaneous translation from/to Russian.

Basic principles of data exchange and project progress

The participants reaffirmed the following principles:

  1. Only 5Æ gridded data to be provided. Raw data will not be made available. Grid should represent point values at the 5Æ nodes.
  2. Derived products (geoid, Bouguer anomaly) to be released along with basic grid.
  3. Russian institutions includes in the Project only data open according to the Russian legislation.
  4. Final product of the Project (digital grid) will be distributed among participant without any restrictions, and later released into general public.
  5. The first phase of the project to be ended fall of this year, with grid preparation by NGA/KMS and distribution following final compilation of "beta-version" grid.
  6. GUNIO/HDNO Russia invited to participate in the Project at any stage (including consideration of possible production of the final map in their mapping department), ref. offer at St. Petersburg workshop.

 

Time schedule

Conclusion of first phase (beta version grid release): end of year 2001. To get a more specific time table for grid preparation etc. (we failed to make a clear agreement here), I suggest:

Deadline for data contribution: ultimo November 2000.

Grid preparation and publishing: February 2002.

There is some time-pressure to publish grid soon, as NASAÆs laser satellite ICESAT will provide altimetry over entire Arctic Ocean by 2002, and thus may make major parts of ArcGP grid outdated.

 

Grid preparation

The following principles were confirmed: The method of least-squares collocation/Kriging is an efficient way to combine data with different resolutions and accuracy, especially when combined with draping of noisy data with bias problems on good data. Some bias problems were pointed out, e.g. apparent base tie problems in some Scicex cruises. Russian data to be converted from state reference system to international gravity datum for optimal geoid determination results, using conversion formula provided by Tsniigaik.

Important to provide some kind of standard deviation/data quality indication along with grid and geoid. Important to avoid data-coverage "artifacts" in final grid (such as e.g. discontinuities along meridians or parallels).

 

Identified desired/missing data to improve beta-version grid and geoid

The chairman of ArcGP (R. Forsberg) identified the following known data sources:

  1. Unprocessed Greenland/Svalbard/Fram Strait airborne data from recent surveys (KMS/AWI/SK-Norway), marine data in Svalbard region (Norway).
  2. Scicex 1999 data in final form (+ tie updates on earlier data).
  3. Final data for Ellesmere Island and bias check on Canadian LOREX North Pole gravity data.
  4. Recent marine gravity data in North Atlantic (NGA/KMS).
  5. Russian gravity data from Frans Josef Land 1993-2000 surveys (from admissible small-scale maps, PMGE).
  1. VNIIO gravity grid compilations from small-scale mapping over eastern Arctic Ocean (VNIIO).
  2. Siberia 10Æ land mean free-air anomaly data north of 64° N (Tsniigaik).

The participants were asked to look for more potential data. It was requested that data as far as possible be contributed during the fall 2001. The participants acknowledged the data contributions released by all countries, especially the major contributions by NGA, NRL and the Scicex program, as well as the potential important contributions from Russia (pending approval of release policy by central authorities). Considering the monumental effort of Russian gravity surveys in the Arctic over decades, the participants recommended that such data be made available to ArcGP at map scales comparable to the general ArcGP data resolution, to result in a high-quality, truly international ArcGP grid and geoid product.

 

Publication and dissemination

It was suggested to make primary distribution of ArcGP results by web and CD-ROM. A printed map is to be compiled, preferably at same scale as the IBCAO international bathymetry map of the Arctic Ocean. Agency to print this map still to be decided. An EOS article planned, with all major data providers as co-authors, to highlight completion of project, followed by a detailed technical report describing grid preparation etc. Geoid computation issues are to be especially addressed in Journal of Geodesy paper. Reports at e.g. EGS, AGU and IUGG conferences by members of the working group should be done to enhance visibility of results.

It was decided that momentum on project is now for completion, and no further working group meeting seems necessary at present.

The participants thanked Marc Veronneau of GSD/NRCan for arranging the meeting, and for holding the ArcGP evening dinner.

Copenhagen, May 29, 2001

Rene Forsberg

Chairman of Arctic Gravity Project

State Geodesist, National Survey and Cadastre (KMS), Denmark (rf@kms.dk)

 

 

 

Participants in ArcGP workshop and business meeting, Ottawa, Canada, May 2001

Tobias Boebel. Optimare Gmbh, Coloradostr. 5, 27580 Bremerhaven, Germany. (0149)471-9615551 / Alfred Wegener Institute, Columbusstrasse, 27568 Bremerhaven. (0149) 471-48311213. tobias.boebel@optimare.de.

Vicki Childers. Naval Research Lab Code 7421, 4555 Overlook Ave SW, Washington DC 20375, USA. (202) 404-1110, fax (202)-767-0167. vicki.childers@nrl.navy.mil.

Bernhard Coakley. Dept. of Geology, Tulane University, New Orleans LA, USA 20118. (504)862-3168, fax (504)865-5199. bcoakle@tulane.edu.

Gleb Demianov. TcNIIGAiK, Onejskaya 26, 125413 Moscow. gleb@geod.ru.

Rene Forsberg, National Survey and Cadastre, Rentemestervej 8, DK-2400 Copenhagen NV, Denmark. +45-3587-5319, fax +45-3587-5052. rf@kms.dk

John Halpenny. Geodetic Survey Division, 4984 û 615 Booth St., Ottawa, Ont., Canada K1A OE9. (613) 996-9321. john.halpenny@nrcan.gc.ca

Joseph Henton. Geodetic Survey Division, 615 Booth St., Ottawa, Ont., Canada K1A OE9. jhenton@nrcan.gc.ca.

Vadim Leonov. Polar Marine Geosurvey Expedition, Pobeda St. 24, 189510 St. Petersburg-Lomonossov, Russia.

Brad Nelson. Institute for Aerospace Research, U-61 Uplands, Ottawa, Ont. Canada K1A 0R6. (613) 998-2210, fax (613) 952-1704. Brad.nelson@nrc.ca.

Doug Hardwick. Box 625, Manotick, Canada K4M 1A6. (613)692-4511, fax (613)692-6184. hardwick@cyberus.ca

Jianliang Huang. Geodetic Survey Division, 615 Booth St., Ottawa, Canada K1A OE9. (613) 947-1043. jianhuan@nrcan.gc.ca.

Per Lyster Pedersen. ASIAQ (Greenland Government Survey Organization), Box 1003, 3900 Nuuk, Greenland. (+299) 348800, fax (+299) 348801. plp@asiaq.gl.

Walter Roest. Geological Survey of Canada, 615 Booth St., Ottawa, Ont., Canada K1A OE9. roest@gsc.nrcan.gc.ca.

Michael Sideris. Dept. of Geomatics Eng., University of Calgary, 2500 University Dr. NW, Calgary, AB, Canada T2N 1N4. (403)220-4985, fax (403)284-1980. sideris@acs.ucalgary.ca

Dag Solheim. Norwegian Mapping Authority, Box 15, N-3504 Honefoss, Norway. +47-32118100, fax +47-32118101. dag.solheim@statkart.no.

Mikhail Sorokin, State Enterprise PMGE, St. Petersburg, Russia. (812) 442-0494, fax (812) 423-1900. mikhail.sorokin@dux.ru

Marc Veronneau. Geodetic Survey Division, 615 Booth St., Ottawa, Ont., Canada K1A 0E9. (613) 992-1988, fax (613) 992-6628. marcv@nrcan.gc.ca.

Andrew Zayonchek. VNIIO, 1 Anglisky Av., 190121 St. Petersburg, Russia. +7(812) 114-2088. andrew@vniio.nw.ru.

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