On the occasion of the fourth International Comparison of Absolute Gravimeters carried out at Sèvres in 1994 an extensive series of microgravimetric measurements was organized. In total, fifteen LaCoste, four Scintrex CG-3M and one Sodin gravimeter measured, within a small network, vertical gravity gradients and a calibration baseline. The results show that the accuracy for single instruments is in the range of 3 μGal to 5 μGal in gravity difference, for the Scintrex and the LaCoste meters. Data from the series were also used to intercompare different ways of calibrating the gravimeter electrostatic feedback systems. The calibration platform of the Institut für Angewandte Geodäsie, (IFAG), Frankfurt, and the calibration lift of the Observatoire Royal de Belgique (ORB) were installed at Sèvres and the results compared with those for the calibration line. This paper gives the first results and a review of the techniques used.
Artificial accelerations are used for the absolute calibration of relative gravimeters. Such accelerations are generated by the Frankfurt calibration system. The system consists of three stepper-motor-driven spindle blocks which can be mounted on any arbitrary body: here in the experiment a platform where spring gravimeters can be placed. The vertical motions of stepper-motor-driven spindle blocks are controlled by glass gauges. In a digital feedback loop, imperfections of the screw can be compensated. The driving functions for the stepper motors are sinusoidal waves with periods between 200 s and 2400 s. With the stroke of the system (± 10 mm) artificial accelerations up to ± 1000 × 10-8 m s-2 can be generated. During the experiment twelve gravimeters were investigated. The calibration factors as well as the frequency transfer functions of the instruments were determined with accuracies of better than 10-3. The results coincide well with the calibration factors derived from the gravity calibration line in Sèvres for the same instruments.
A new miniaturized absolute gravimeter has recently been developed to aid in the acquisition of absolute gravity for geophysical investigations and survey applications. The new instrument is much smaller than previous absolute gravimeters and can acquire data at a much higher rate. This technology will enable the development of a new generation of land, marine, and airborne absolute gravimeters.
The absolute gravimeter is based upon a direct measurement of the acceleration of a test body in free‐fall using a very precise laser interferometer. A small reflective test‐body is launched into the air for about 7 cm and tracked using a precise laser over its symmetric rise&fall path of over 200 ms. These individual measurements can be repeated very quickly, at a rate of 2 throws/second.
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