Potsdam Correction from the Satellite Determined Geopotential

Abstract

THE absolute value of the acceleration due to gravity at a point on the Earth's surface has generally been measured using reversible pendulums. Recently, however, the method of free fall determinations of gravity¹ with its several variations has become increasingly popular because of the availability of electronics sophisticated enough to measure precisely the very short intervals of time involved. Generally, however, the absolute measurements of gravity are expensive, cumbersome and time-consuming; consequently, they are made only at a few selected points called “bases”. The high accuracy of relative measurements achievable with the modern gravimeters has made it possible to find the absolute gravity at any other point by measuring the gravity difference relative to one of these bases. For the sake of uniformity, it seems desirable to select one reference base. The Pendelsaal of the Geodetic Institute, Potsdam, East Germany, has been accepted as the reference base since the beginning of the twentieth century and the international network of relative gravity measurements is tied to it to form the “Potsdam gravity system” Until recently, the value of absolute gravity adopted at the Potsdam site was g=981,274.00 mgal, as determined by F. Kühnen and Ph. Furtewängler from reversible pendulum measurements during the period 1898–1904. But modern re-examinations of this value have shown that it is in error by about −10 to −15 mgal. This means that the whole system based on this value has a constant scale error; the fiftieth general assembly of the International Union of Geophysics and Geodesy, held in Moscow in August 1971, has therefore recommended that a correction of −14 mgal (based on some of the most recent determinations) should be applied to the Potsdam gravity value.