Large-Scale Absolute Gravity Control in Brazil

Abstract

Since 1986, IfE Hannover operates the absolute gravimeter JILAG-3. After laboratory and field experiments, hard- and software improvements, as well as comparative measurements at absolute and relative stations, the instrument has been employed for absolute gravity control in fundamental and geodynamic networks in central and northern Europe. At approximately 100 gravity determinations at about 60 different stations an average station precision of a few μgal (1 μgal = 10 nms ^-2) could be achieved by 500 to 2000 drops. Taking residual instrumental and local effects into account, the average accuracy is estimated to be 10 μgal.

A large-scale control survey has been scheduled and partly performed in 1988/89 in South America, in cooperation with national University Institutes and state agencies. This control system shall cover about 2/3 of South America by establishing more than 20 absolute gravity stations with additional local eccenters. The gravity stations shall partly serve as stations of the International Absolute Gravity Basestation Network (IAGBN) proposed by the International Association of Geodesy (IAG), and will also provide gravimeter calibration lines in the countries involved. By connection to the national gravity networks, I.G.S.N.71 in South America will be improved and densified. After an observation campaign in Venezuela in 1988, a project in Brazil has been performed from February to March 1989 in cooperation between IfE and UFPR, covering the country with seven stations. Objectives of the project and first results of the measurements are presented and discussed in the paper.