抄録
Simultaneous observations of crustal tilt with collocated two characteristically different types of water-tube tiltmeters have been carried out at the Esashi Earth Tides Station since April 1980, one of which was designed at the International Latitude Observatory of Mizusawa (namely WTT(M)) and the other at Nagoya University (WTT(N)). Major differences between them are in supporting systems of the floats, sensors and the diameters of the water-tubes. Main purpose of this investigation is to verify the reliability of tilt observation with water-tube tiltmeter, establishing a method of precise calibration. In this paper, a method to derive sensitivity coefficient purely experimentally is proposed. This enables us to calibrate the instruments within an error of about 1.5%, which can be reduced to less than 1 % by making more careful measurements of cross-sectional areas of the floats and the vessels at the level of free surface of water. The results of tidal analyses for observations during about 21 months are also given. Both amplitudes and phases of six major tidal constituents (Q1, O1, K1, N2, M2 and S2) obtained by WTT(M) and WTT(N) are found to be very close to each other. This suggests that these watertube tiltmeters yield no systematic differences and serve for reliable tidal observations.
