Accuracy of Levelling of High Precision in Japan

Abstract

In this paper, the writer investigates the accuracy of the levellings of high precision which have been carried out by the Geographical Survey Institute in Japan. The main resulted conclusions are as follows: (1) The standard deviations of the measured values resulted by the levelling surveys are ±2030 mm/km. The misclosures in one third level-circuits of all excess the limitation of misclosure, 2.0 mmVL (km), where L is the length of a circuit. Almost of all the misclosures of level-circuits whose lengths are shorter than 100 kilometers keep within the limitation of misclosure, while one-half that of which the lengths are longer than 600 kilometers goes over the limitation. (2) The gravity corrections to the closures of level-circuits are shown in Fig. 3 and Table V. The difference between the closure in level-circuit corrected the normal orthometric correction by the normal gravity value and that corrected the gravity correction by the measured gravity value is 34.2 millimeters in maximum. (3) The standard deviations of elevations of the bench marks, as shown in Figs. 4(a) and 4(b), are 12 cm in Kanto district, 34 cm in Chugoku and Tohoku districts, and 46 cm in Kyushu and Hokkaido districts. Roughly speaking, the error of the adjusted elevation of a bench mark increases in proportion to the distance of the levelling route from the datum in Tokyo to its bench mark.