Report of Workshop: Airborne Gravity and the Polar Gravity Field

Greenland, June 1998

The international workshop on Airborne Gravity and the Polar Gravity Field was held in Kangerlussuaq (Sondre Stromfjord), the major airport base of Greenland, in the days June 2-4, 1998. The workshop was organized and sponsored by the National Survey and Cadastre of Denmark (KMS), with additional economic support from the Commission for Scientific Research in Greenland and the International Association of Geodesy.

The workshop was called in response especially to the developments in recent years of airborne gravity surveying, allowing for the first time a practical means of surveying the remaining polar gaps in the global gravity data coverage, thus improving global gravity field models and geoids of the future, as well as giving new insights into the tectonics of the Arctic and Antarctica. The workshop was also organized in order that specialists in gravity surveys and interpretation could discuss methods and techniques under informal terms. The workshop was coinciding with initiation of KMS airborne gravity measurements in the area, and the workshop included a tour of the KMS Twin-Otter aircraft installation. University of Calgary, Canada and BKE, Germany also provided inertial gravity measurement units, which on an experimental basis were mounted along with a conventional gravimeter, and used for a joint test flight immediately following the workshop.

The workshop attracted 28 scientists involved in gravity or airborne remote sensing from a number of countries: USA (5), Canada (4), Germany (4), Russia (3), Norway (3), as well as scientists from Portugal, Spain, Sweden and Denmark, with a corresponding number of presented papers and posters. The program was organized in the sessions: Aerogravity review and projects, Global gravity field, Aerogravity systems, Error models, and hardware and GPS, surface gravity and related geophysical data. To limit the workload, and to enhance the informal nature of the workshop, it was never planned to publish proceedings.

The papers presented ranged widely, from theoretical studies of methods to reviews of major ongoing projects such as the NRL (J. Brozena), AWI (U. Meyer) and Russian (V. Leonov) airborne Arctic and Antarctic gravity data collection activities. Accuracy seems to range from 2 to 5 mgal, with resolution often at 10-15 km, depending on aircraft speed and filtering parameters. Slower airspeeds gives possibility for higher resolution (e.g., illustrated by papers of the AGMASCO project). A number of papers also dealt with new inertial-based hardware, utilizing either existing lasergyro inertial navigation systems (Glennie, Bruton, Colomina) or own developments (Cunha, Boedecker), which - when developed for routine use - would circumvent some of the problems of the currently used gyro-gimballed gravimeter systems. Accuracies of a few mgal seems to be possible currently.

A major new information for western participants was a presented compilation of russian gravity, magnetic and bathymetry data in the Arctic (Maschenkov and Zayonchek), illustrating the monumental Polar scientific efforts undertaken in decades by the former Soviet Union (and now Russia), through icebreaker, airborne and ice camp expeditions. On the global level presentations were made on the recent EGM96 global reference field, as well as Russian global models (Demianov), emphasizing the importance of the polar areas for improving future such models. On the methodological presentations, papers dealt was such topics as improved filtering and off-level corrections of airborne platform gravimeter systems (Childers, Olesen), downward continuation (Rubek), and papers on data fusion, global representation and inversion (e.g., Strakhov, Strykowski). Additional papers described projects relating to surface gravity data, comparisons to satellite altimetry, SAR interferometry, and ongoing magnetic projects in the Arctic.

During the workshop, discussion periods addressed future developments in aerogravity, the current status of commercial activities, and possibilities of a future polar gravity field project - especially compiling available Arctic gravity data. For Antarctica an initiative has recently been started to compile existing gravity data as a spin-off of a magnetic compilation project (ADMAP project). Discussions also included near-linguistic issues: What is the meaning of such frequently used terms as accuracy from cross-over analysis (divide r.m.s. cross-overs by the square-root of 2 or not?) and (full-wavelength or half-wavelength?). It was apparent that a common language was needed between the different groups currently active in airborne gravity measurement and accuracy evaluation.

With the location at a former US air base site, social activities included a bowling tournament, an outdoor Musk-Ox barbecue (accompanied by millions of hungry mosquitoes), and a wildlife excursion (and, for the associates, a chance low-level glacier flight). It is hoped that the good spirit of the workshop will continue in future workshops and practical scientific gravity cooperation among the participants.

Reported by the workshop organizer: Rene Forsberg, KMS, Denmark

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