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Advantages of close line spacing in airborne gravimetric surveys

Sander Geophysics, Ottawa, Canada

John Peirce and R. A. (Bob) Charters

GEDCO, Calgary, Canada

Corresponding author: stephans@sgl.com

Editor's note: The Meter Reader is a regular column in TLE, coordinated by John Peirce, that seeks to highlight new ideas in geophysical fields besides seismic—particularly gravity, magnetics, and electromagnetics. If you have a short contribution on these topics that is written in the relatively informal but informative style of TLE, please submit it to Dean Clark, editor of TLE in Tulsa, or to John Peirce, at GEDCO in Calgary. This month's article is a discussion of some new ideas on the most effective way to design airborne gravity surveys, which is a logical sequel to several earlier articles on different airborne gravity systems and the resolution each can achieve. The ideas expressed in this paper are not yet widely accepted, so alternate opinions on this topic are most welcome!

The first 20% of the full text of this article appears below.

Line spacing for airborne gravity surveys is one of the factors that can influence the accuracy and resolution of the resultant gravity grids. Sander Geophysics has flown several recent surveys with close line spacing to increase the accuracy and resolution of gravity data. Close line spacing improves the data in several ways. Filtering between adjacent lines reduces data acquisition noise on the grid data. Closer line spacing allows using the flight data to compute a better digital elevation model; this can, in turn, be used to improve the gravity terrain corrections. Closely spaced adjacent lines can also be used for quality control and to aid in data processing.

Airborne gravity surveys have, in the past, been flown for regional mapping of the gravitational field, with survey line spacing of 3 km or more, because of the resolution limitations of most airborne gravity systems. Sander Geophysics has found that surveys flown with significantly closer line spacing (from 50 m to 1 km, depending on the survey objectives) can significantly improve the accuracy and resolution of the gravity data. We recently undertook a detailed study to investigate the quantitative improvement that can be realized by using such close line spacing. The results from this study make a compelling argument for closer line spacing in airborne gravity surveys.

In order to demonstrate the advantages of closer line spacing surveys we have evaluated some data flown with Sander Geophysics' AIRGrav system in 2001. The survey described here was a large AIRGrav survey flown in Western Canada over the Turner Valley area, a well known oil and gas producing region south of Calgary, Alberta (Figure 1). The survey area covers the foothills of the Rocky Mountains, and the general trend of the geology in the area is north-northwest/south-southeast. A total of 12 500 . . . [Full Text of this Article]