Tokyo Surface Ship Gravity Meterα-1

Abstract

In the "Tokyo Surface Ship Gravity Meter" which was designed in 1960 and completed in 1961, a dynamic gravity meter is mounted directly on the gimbals stabilized by a vertical gyroscope, and is kept vertical. Variations in the vertical acceleration are converted to frequency variations through a dynamic gravity meter and are digitally recorded on punched tapes. Variatoins in the acceleration of gravity due to the motion of a vessel do not contain the shorter period components compared with the disturbing vertical accelerations caused by ocean waves. This enables us to detect the gravity variations from those unacceptable disturbing accelerations by means of a low pass filter. In the "Tokyo Surface Ship Gravity Meter" this operation is carried out by means of digital filtering with the aid of a digital computer. Introduction The essential techniques in a surface ship gravity meter are, firstly, the method of separating the gravity variations and the vertical accelerations caused by the motion of vessels and secondly, the method of keeping the vertical of a gravity meter to measure the vertical component of the accelerations. In the "Tokyo Surface Ship Gravity Meter" which was designed in 1960 and completed in 1961 (Photo. 1, 2. Fig. 1.), a dynamic gravity meter is mounted directly on the gimbals stabilized by a vertical gyroscope, and keeps its vertical. Variations in the vertical acceleration are converted to frequency variations through a dynamic gravity meter and are digitally recorded on punched tapes. Variations in the acceleration of gravity caused by the motion of a vessel do not contain the shorter period components compared with the disturbing vertical accelerations caused by ocean waves. This enables us to detect the gravity variations from those unacceptable disturbing accelerations by means of a low pass filter. In the "Tokyo Surface Ship Gravity Meter" this operation is carried out by means of digital filtering with the aid of a digital computer. In our previous short period bifilar gravity pendulum [1], force, acting on the mass M, is transmitted to the pendulum through a spring and a powerful liquid damper to reduce the effects of the disturbing accelerations. Such an analogue low pass filter, as is used in the Askania Gss [2] or LaCoste Romberg surface ship gravity meter [3], is required to have an excellent lineality. Hence, in the "Tokyo Surface Ship Gravity Meter ", it is tried to solve this problem by the use of a digital 117 Tokyo Surface Ship Gravity Meter ƒ¿-1