Research On Low Power-consumption In-situ Calibration Dual-mode Magnetometer

Geomagnetic measurement is an important method in marine geophysical survey. The requirements of the accuracy and resolution of the geomagnetic measurement are higher and higher, from the satellite magnetic survey, the airborne magnetic survey, the shipborne magnetic survey, the marine towed magnetic survey, to the near seafloor magnetic survey. With the rapid development of quantum measurement, MEMS fabrication and deep-sea technologies, a novel seafloor magnetometer of high integration, low power consumption and taking into accounts both accuracy and engineering practice become possible.There are two types of marine magnetometer. One is the scalar magnetometer based on atomic effect in geomagnetic field, which can provide higher precision of the total value of magnetic field. The other is vector magnetometer based on the measurement of induction magnetic field on the orthogonal three axes of the sensor, which can give magnetic vector and with higher engineering adaptation. Due to the limitation of size, power consumption and circuit complexity,it is difficult to embed the two types of magnetic measurement into one magnetometer. In this paper, a novel design based on complementary integration of rubidium optical pumping technology and magnetic fluxgate technology is put forward. The in-situ calibration method of underwater vehicle magnetism, the geographical three components readout of magnetic vector and engineering adaptation have been intensively researched.Based on the design of overall system, the design of miniature vapor cell and the design of the integrated circuit, the miniaturization and low power consumption of the seafloor dual mode magnetometer is realized. Accordding to the requirement of engineering application, the complementary advantages of the two modes of scalar and vector magnetic measurement are considered in the functional design. The measurement of the total field and three components of geomagnetic field at the same time has been realized, which reduces the initial sweep time and data loss probability of scalar magnetometer, and improves the absolute accuracy of the vector magnetometer.When equipped on underwater vehicles, the magnetometer is susceptible to interference with the body of ferromagnetic material, which is the bottleneck of near seafloor magnetic survey. By comparison and analysis of current various magnetic calibration algorithm, a fast in-situ calibration algorithm based on least square method and particle swarm optimization is proposed and implemented. The algorithm is evaluated by the measured data, and the effectiveness of the algorithm is verified by lake test and sea trial.Compared with the high precise scalar magnetometer and vector magnetometer in Hangzhou geomagnetic station, the qualification of the dual mode magnetometer developed in this paper are evaluated. Considering the application method, the dual-mode magnetometer was equipped with "Qianlong 2" AUV, tested in the Qiandao Lake and the South China Sea respectively. The lake trial and sea trial verify the effectiveness of applying this magnetometer in near seafloor magnetic survey. Jointed by seafloor observatory near ZhanRuoShan Island of Zhoushan, the dual mode magnetometer was tested, and the effectiveness of applying in seafloor geomagnetic observation over long time is verified.The three components of geomagnetic field are of great value for the magnetic inversion of the seabed geological survey, but it is necessary to transform the data output from the instrument coordinate system to the geographical coordinate system. This paper designed and implemented the inertial measurement unit without magnetic aided, which can provide three dimensional attitudes of the seafloor magnetometer in real time, to readout the geomagnetic vector directly in geographical coordinates system.