A new miniaturized magnetometer system for long-term distributed observation on the seafloor

Abstract

We have developed a new magnetometer system specialized to multipoint and long-term observations on the seafloor to promote marine or ocean-bottom experiments mainly for the electromagnetic sounding of the Earth’s interior. In situ magnetic field observation on the seafloor is an essential geophysical technique to investigate structures of the oceanic crust and the upper mantle, many of which are still frontier as to observational evidences. The in situ and long-term observations require long-term-operable and small-size magnetometer systems, which are placed on the seafloor over a year in pressure-resistant cases without external power supply and communication. We have designed and developed a new electric circuit board of small size and lower power consumption for the magnetometer system. Our new magnetometer system, what we call “DOKODEMO MAG,” is suitable to be installed in a pressure-resistant cylinder of 36 mm diameter and can operate independently over 2 years with a smaller amount of batteries than the conventional system because its power consumption was saved to ~ 33 mW. This magnetometer system is capable of observing orthogonal three-axis magnetic fields continuously with sampling frequency of 5 Hz at maximum and an accuracy of ~ 0.1 nT. The system also records tilt and temperature of the system and voltage of the batteries. Prototype models of this magnetometer system were tested for in situ operation for 5 months on the seafloor around the Kikai caldera in the south of the Kyusyu Island, SW Japan. The results of the test showed sufficient performance of our new magnetometer system and its potential of future usage for every type of marine or ocean-bottom operations.[Figure not available: see fulltext.].