Investigation Of Non-linear Change Of Vertical Gradient Of Gravity

The high-precision absolute gravimeter’s accuracy is up to1—2μGal，its main applicationis to research the gravity changes with time and to provide the datum and constraint to thegravimetric connections. To provide the datum and constraint, the absolute measurement of theinstrument measurement’s effective height should be reduced to the ground surface. Thereforethe precise measurement of the vertical gradient of gravity determines the accuracy of the groundabsolute gravity datum to a great extent. Furthermore, in using the FG-5and A-10absolutegravimeter to establish the absolute gravity datum respectively, the effective heights of the twogravimeters are different (the effective height of the FG-5gravimeter is about130cm and theA-10gravimeter is about80cm),so the non-linear change of gravity’s vertical gradient may havean effect on the reduction results. This article will make a further research on the measurement ofthe gravity’s vertical gradient and its non-linear changes to demonstrate the existence of thenon-linear change of the gravity’s vertical gradient and its effect on the high-precision absolutegravimeter’s measurement.The main researches and contributions are fourfold:1、Establish various terrain models on the basis of the actual terrain conditions and calculatethe non-linear change of gravity’s vertical gradient to provide the basis of the observationscheme’s program development and improvement.2、Make multiple close round trip conjunction measurements between80cm,130cm heightand the pier surface at28representative absolute gravity points using two CG-5relativegravimeters and two Burris gravimeters. Determine the gravity’s vertical gradient and estimateits accuracy.3、To validate the non-linear change of the gravity’s vertical gradient effectively,we conductfurther experiments between Qinling Fengyukou and The second monitor center of Chinaearthquake administration. Consider different absolute gravimeters’ effective height, in themeanwhile, add the100cm height on completing the vertical gradient measurement to achievegravity’s vertical gradient measurement results of multi-heights and its fitting equation.4、Analyze the non-linear change of the gravity’s vertical gradient according to the gravity’svertical gradient measurement at each point. The experiment result indicates that the non-linear change of the gravity’s vertical gradient exists in specific terrain conditions. Its maximal changecould be up to0.125μGal/cm. This result agrees with the theory result.