Improvement of the gravity network with absolute gravity measurements

Abstract

The First-Order Gravity Network of Japan which consists of about 300 gravity stations plays an essential role in gravimetry in Japan. The network gives reference datum for all the gravity measurements. Since 1985, Geographical Survey Institute has been carrying out absolute gravity measurements at 12 stations with a Sakuma-type absolute gravimeter to improve the accuracy of the network. Results of absolute gravity measurements revealed that the precision and repeatability of absolute gravity values obtained were higher than 10μGals. Test adjustment of a part of the network showed that the precision of gravity values controlled by absolute gravity measurements is higher than 10 μGals. Gravity measurements in this network will be repeatedly performed at 5 to 7 year intervals together with geodetic leveling. With those measurements, gravity changes associated with vertical crustal movements of up to a few centimeters can be detected throughout Japan. The combination of precise gravity measurements with precise levelings is a powerful tool to clarify the underground physical process which causes vertical crustal deformation. © 1992, The Geodetic Society of Japan. All rights reserved.