IMPROVEMENT OF OBSERVATION ACCURACY OF THE LACOSTE‐ROMBERG (MODEL D) GRAVITY METER BY SUPPLEMENTARY INSTALLATION OF ELECTRONIC FEEDBACK¹

Abstract

Recent years have seen an increasing need for high‐precision gravity meters. A widely used and the most accurate one is the LaCoste‐Romberg, model D (LCR‐D) meter, equipped with electronic readout. According to the manual the reading accuracy is 5 μGal. A way of reducing most of the instrumental factors limiting the accuracy is the use of an electronic feedback system. We have fitted the LCR‐D 34 with a Schnüll‐Röder‐Wenzel, model D (SRW‐D) feedback. After installation the readout voltage was calibrated, the instrumental behaviour tested, and the accuracy of the system determined. By repeat readings in the laboratory without moving the meter, the standard deviation for a single reading is better than 4 μGal in normal mode and better than 1 μGal in feedback mode. The accuracy of gravity differences ‐ this is usually observed in field practice ‐ is the mean value of the repeat errors of several sets of differences observed in a short time to avoid any corrections. This accuracy is better than 9 μGal in normal mode and better than 5 μGal in feedback mode. With this, the accuracy of a single reading becomes more than 6 μGal and more than 3 μGal, respectively. As the described improvement of accuracy was found to be not as good as expected, additional improvements should centre on the use of electronic levels instead of the standard liquid ones.

Evaluation of Shipboard and Satellite‐Derived Bathymetry and Gravity Data Over Seamounts in the Northwest Pacific Ocean

“…It is now possible, for example, using modern versions of the Lacoste‐Romberg air‐sea and the Bell Aerospace BGM gravimeter together with GPS modern navigation to obtain an accuracy of 1–2 mGal and resolution of 2–10 km over the deep ocean, depending on sea state (Bell & Watts, 1986; Hildebrand et al, 1990). Moreover, the reporting of sub‐mGal accuracies and higher resolution from some sea gravimeters (Casten & Haussmann, 1990) and gravity gradiometry (Bell et al, 1997), in which the full tensor field is measured, provide an exciting prospect for future work.…”