Abstract
What has so far made it difficult for us to precisely measure terrestrial gravity on a ship in real time, is the fact that it had not been easy for us appropriately to separate a gravitational shift due to an Etovös effect from an acceleration due to a heaving motion of a ship.
The Etovös effect is defined as a gravitational shift arising from a horizontal movement of a ship. Accordingly, if we want to measure gravity correctly on board, then we must properly compensate the errors resulting from the gravitational shift on the basis of the ground velocity of the ship.
By a method entitled above, Japan Hydrographic Department has recently succeeded in measuring a gravitational anomaly in real time efficiently and precisely, there by obtaining the correct gravity.
While the conventional methods, at first, detect and eliminate the errors one by one which are involved in the primary data on the gravity measured, the ground velocity of a ship, Etovos effect, and the depth of the sea, and then determine the gravitational anomaly, the proposed method determines the gravitational anomaly directly from those data, and after that, smooths the results thus determined to obtain the correct gravity.
Adoption of this method has significantly usable the results obtained from measurement of the gravity in the vicinity of a turning point of a ship, where the measurement has never been carry out. It has raised to nearly 100 percent, of the utilization of the primary data on the gravity thus measured.
