The national wide gravity survey to establish gravity values for the base reference stations in Korea was initiated by the U.S. Army. The Division of Geodesy, U.S. Army Map Service Far East (DG, USAMSFE) conducted two base station surveys in 1961 and 1964, and measured gravity values at 15 stations throughout Korea. Professor Woollard also observed 3 gravity base stations in 1964 as a part of the International Gravity Measurements. All of these surveys were tied directly to DG Base of USAMSFE in Tokyo and Tachikawa Air Force Base stations. GMIK (presently Korea Institute of Energy and Resources) also made 10 base station measurements in 1971, which are tied to USAMSFE base stations established in the previous survey. In a broader sense, all of these measurements are related to Potsdam system whose value is now recognized to be too large by about 14 mgals. In accordance with the International Gravity Standardization Net 1971 (IGSN 71), adopted and recommended by the International Union of Geodesy and Geophysics, GMIK, in cooperation with Institute of Geological Sciences of England, measured gravity values at 15 base reference stations which are tied to IGSN 71 primary base stations in London and Kyoto. The results of this survey are generally lower by about 13.8 mgals than previous values. On the other hand, the National Geography Institute established a fundamental national gravity base reference station in the back yard of the Institute's building and determined the gravity value, which is tied to the IGSN 71 value of the base reference station located in Tokyo. The measurements were made twice in 1975 and 1980 with the cooperation of Japan Geophysical Survey Institute. NGI also established four auxilliary gravity base reference stations in 1980. The author recently measured the gravity difference between two base reference stations located in Korea Institute of Energy and Resources and National Geography Institute and found the measured value is different by more than 1 mgal to that computed from the gravity values adopted by two Institutes. Therefore it is recommended to conduct a more detailed crosscheck to establish consistent base reference values throughout the country.

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