The Greenland Aerogeophysics Project: Year 1

John M. Brozena and Mary F. Peters

Abstract:	The Greenland Aerogeophysical Project (GAP) is a joint effort of the Naval Research Laboratory and the Naval Oceanographic Office in collaboration with the National Oceanographic and Atmospheric Administration and the Danish National Survey and Cadastre to map using airborne methods the gravity, magnetics and topography of the entire island of Greenland. The first year of the Greenland Aerogeophysical Project (GAP) has been completed and, at the time of this meeting, the second field season is beginning. During the first field season thirty one flights of a long-range P-3 Orion aircraft were flown over the southern half of Greenland, successfully collecting more than 100,000 line km of airborne gravity, radar profiles and magnetics data. Kinematic interferometric GPS between multiple short or zero- baseline airborne receivers and several sets of stationary GPS receivers provides precise three-dimensional positioning for the airborne sensor system. Besides the GPS receivers these sensors include: LaCoste-Romberg and Bell gravimeters; 10 and 95 GHz radar altimeters; a laser altimeter; raw and processed INS outputs; and a proton-precession magnetometer. Analysis of the data t?om the first field season is still underway, but preliminary results indicate that the gravity, topography and magnetics will be of good quality. The most problematic data set for reduction is the kinematic GPS. The multiple receiver technique employed for the detection and correction of cycleslips generally worked quite well. However, the duration of the flights (approximately 8 hours), the long baselines (well over loo0 km in some cases) and the requirement to fly through periods of poor satellite coverage and geometry make the determination of the exact integer phase-biases very difficult or impossible at times. The aircraft positioning accuracy tends to be best (a few decimeters) near the beginning and end of each flight and degrades to a few to more than ten meters near the middle of the flights. However, the overall accuracy of the gravity and topographic profiles is then significantly improved by performing a cross-over miss-tie analysis and adjustment of the aircraft heights at the hundreds of track intersections produced by the survey tie-lines. The aircmft heights are also absolutely constrained at the ends of each track by the radar heights over water. In these places the GPS ellipsoidal height of the aircraft is adjusted to fit the radar height over the water plus a model geoid height. The airborne geophysical method permits the collection of data along evenly spaced tracks without regard to the logistic difftculties encountered on ground surveys. This leads to much more uniform spatial coverage and much better input for gridded geodetic and geographical data sets.
Published in:	Proceedings of the 48th Annual Meeting of The Institute of Navigation (1992) June 29 - 1, 1992 ANA Westin Hotel Dayton, OH
Pages:	385 - 394
Cite this article:	Brozena, John M., Peters, Mary F., "The Greenland Aerogeophysics Project: Year 1," Proceedings of the 48th Annual Meeting of The Institute of Navigation (1992), Dayton, OH, June 1992, pp. 385-394.
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