High tilt susceptibility of the Scintrex CG-5 relative gravimeters

Abstract

We report on the susceptibility of the Scintrex CG-5 relative gravimeters to tilting, that is the tendency of the instrument of providing incorrect readings after being tilted (even by small angles) for a moderate period of time. Tilting of the instrument can occur when in transit between sites usually on the backseat of a car even using the specially designed transport case. Based on a series of experiments with different instruments, we demonstrate that the readings may be offset by tens of $\upmu$Gal. In addition, it may take hours before the first reliable readings can be taken, with the actual time depending on how long the instrument had been tilted. This sensitivity to tilt in combination with the long time required for the instrument to provide reliable readings has not yet been reported in the literature and is not addressed adequately in the Scintrex CG-5 user manual. In particular, the inadequate instrument state cannot easily be detected by checking the readings during the observation or by reviewing the final data before leaving a site, precautions suggested by Scintrex Ltd. In regional surveys with car transportation over periods of tens of minutes to hours, the gravity measurements can be degraded by some 10 $\upmu$Gal. To obtain high-quality results in line with the CG-5 specifications, the gravimeters must remain in upright position to within a few degrees during transits. This requirement may often be unrealistic during field observations, particularly when observing in hilly terrain or when walking with the instrument in a backpack.