Kinematic Positioning with DGPS: Expanding Frontiers in Aerogeophysics

Robin Bell

Lamont-Doherty Earth Observatory

INTRODUCTION

In 1995, the National Research Council published a report on “Airborne Geophysics and Precise Positioning” (National Research Council, 1995) Much of the material presented here is summarized from that report, although this discussion focuses on the differential GPS applications exclusively.

Airborne geophysics has long been used for regional studies of remote and inaccessible areas. Recent developments in precise positioning of aircraft with the Global Positioning System (GPS) have greatly expanded the range of previously intractable science problems which now can be addressed with airborne techniques (i.e. Brozena et al, 1992). Differential GPS techniques for modern aerogeophysical studies include both real-time navigation of the aircraft and post-mission recovery of the precise positions for data reduction. Major science problems which have been addressed recently with aerogeophysics include deciphering the dynamics of the world's major ice sheets, imaging surface displacements due to earthquakes and decoding the structure of the continental lithosphere. Airborne studies often recover higher resolution data than can be retrieved with satellite technology. Subsequently the aircraft based approach fills a unique niche where land and ship based operations are expensive, difficult or even impossible (Figure 1 and Figure 2).

Broad spectrum instrumented aircraft have demonstrated the capacity both to pursue process-oriented science questions and to survey unexplored regions. An example of an application of such airborne technology is identification of active volcanism beneath the West Antarctic ice sheet (Blankenship et al, 1992). The presence of this volcano has important ramifications for the stability and dynamic processes which govern the ice sheet (Figure 3). This feature was undetected before the application of high resolution airborne surveys, despite the imaging of this area by satellites and the traversing of this region by surface vehicles. Expanding high resolution airborne technology to recover even shorter wavelength signals will have important applications in the resource and environmental industries. Accurate navigation and precision position are critical to the recovery of these shorter wavelengths.

Aerogeophysics today are being used for several major research strategies, for long wavelength reconnaissance studies of unknown areas high resolution studies of detailed processes and for precise monitoring studies. Differential GPS continues to play a major role in the development of all these research strategies. The precise positioning and accurate navigation permit the acquisition of high resolution systematic data sets especially in inaccessible areas such as regions characterized by rugged terrain, dense vegetation or surface hazards which can range from political instabilities to glacial crevasses.

FIGURE 1 Land gravity measurements (dots) and marine gravity surveys (lines) of coastal Gabon. The land measurements were made principally on roads close to major cities. (Data from Watts et al., 1985).



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