- Copyright © 2000 Society of Exploration Geophysicists
Editor's note: Several new systems have been recently developed for acquiring airborne gravity data and airborne gravity gradiometry data. Therefore beginning with this month's Meter Reader column, a special series of columns will spotlight all commercial systems that are now available to the exploration industry. First in this series is a paper delivered by Sander Geophysics Ltd. at the SEG Annual Meeting and Exposition in Calgary, 2000. Successive TLE Meter Reader columns will feature systems developed and/or operated by BHP Minerals, Fugro Airborne Surveys, Carson Services Inc., and Edcon Inc.
Sander Geophysics (SGL) has developed an airborne gravimeter system that uses three orthogonal accelerometers mounted on a three-axis, gyroscopically stabilized platform. The system, called AIRGrav (Airborne Inertially Referenced Gravimeter), was designed specifically for airborne use. This has resulted in an instrument with significant advantages over the modified sea gravimeters commonly used for airborne surveying; the main benefit of the new instrument is that it is more stable in attitude and less subject to noise from horizontal accelerations.
As a result, surveys can be flown under much less favorable flight conditions than needed by other systems, making its operations more economical. Test results show no appreciable degradation of signal quality due to moderate turbulence. Good gravimeter data have been obtained under aircraft accelerations up to 4 m/s2 (peak to peak) for turbulence with a frequency of 2 Hz.
It is almost impossible, when performing airborne surveys, to avoid some degree of air turbulence. The resulting horizontal and vertical accelerations of the aircraft can be on the order of hundreds of thousands of mGal. Even a very slight deviation of the gravity sensor from the vertical will influence the gravity measurements. Vertical accelerations of the aircraft combine directly with the measurement of gravity. Our gravimeter system addresses these issues in a …