Measurement of Tilt of a Frozen Sea

Abstract

IN May 1967, as part of a programme of geodetic studies in the vicinity of the North Pole, an attempt was made to measure the tilt of the fluid surface of the Arctic Ocean. Three holes were drilled through the ice and the tilt relative to the equipotential surface was determined by levelling from hole to hole with a levelling instrument¹. Two sets of observations were taken at a distance of about 56 km from the North Pole on May 11 and 13, 1967. Both measurements showed a downward tilt of 8 ± 2 seconds of arc in the direction of 100° and 150° west of Greenwich, respectively. This experiment showed that, if the measurements are correct, large ocean tilts in the polar region may occur. However, because of atmospheric refraction, this technique is not suited for the desired degree of precision and the search for a better method led to the development of a hydrostatic levelling system that was tested in the vicinity of the North Pole in April and May 1969 and in the Gulf of St Lawrence in March 1970².