Vibration-induced drift in LaCoste and Romberg Geodetic Gravimeters

Abstract

Many hitherto unexplained erratic gravimeter measurements can be attributed to the effect of vibration on the gravimeters during transportation between gravity stations. Experiments with four LaCoste and Romberg land gravimeters on a vibrating platform showed that all are affected to some degree by forced vibrations at frequencies and peak accelerations that can occur on common carriers. Two effects were found: all four gravimeters when subjected to vibration in the 35‐ to 70‐cps range for 1 min or more at peak accelerations of about ±1 g drifted erratically in the ±0.1‐mgal range; at about 48 cps positive drift as rapid as 1 mgal/min sometimes occurred. The threshold of acceleration needed to produce this unidirectional drift varied from ±0.5 to ±2.0 g for the meters that were tested. As there is extensive documentation to show that vibration of these intensities may occur at frequencies in this range in aircraft or land vehicles, it is concluded that vibration is the major cause of the inconsistent performance that is occasionally observed on these instruments. In experiments with foam rubber and mechanical isolators to minimize the effect of the ambient vibration field, it was found that by using mechanical isolators to support the gravimeter within the carrying case it was possible to eliminate the unidirectional drift at accelerations of ±2 g.

Space-Wise approach for airborne gravity data modelling

“…Note that in order to perform the RTC the digital elevation model is smoothed using a moving average window, with a spatial resolution that depends on L max , given by Lambeck (1990): (Hamilton and Brul 1967). The above procedure represents our remove step that leaves the reduced observations δg red obs and the reduced reference signal δg red ref with zero mean, smaller amplitude and spatial correlation with respect to the original ones.…”

Adjustment of Gravity Observations towards a Microgal Precision

“…It is a slow and progressive variation with the time [6,10]. The drift rate depends on the conditions which the gravimeter is submitted [11,12]. The better procedure is to assume a drift rate for each gravity interval, removing the drift prior to the adjustment to avoid an over parameterization in processing.…”

Gravity base ties and gravimeter calibration line in western Saudi Arabia

“…Lacoste-Romberg gravimeters G328, G330, G506, and G511 were used,and were transported in their padded cases strapped to the aircraft floor on pads. Aircraft-type antivibration mounts would have been desirable to minimize vibration-induced gravimeter drift (Hamilton and Brule, 1967), but one only was available, for gravimeter G330. Flight conditions generally were good, except for leg E ( fig.…”