Fundamentals and Theoretical Models of the Geomagnetic Navigation and Positioning

The geomagnetic field is a fundamental geophysical field (M.-L. Zhang, in Introduction to geophysics. Petroleum Industry Press, pp. 23–25, 2019), which consists of the Earth's internal and external magnetic field. Among them, the internal magnetic field mainly consists of the main magnetic field formed by the Earth's core and the crustal anomalous field formed by the lithosphere, which accounts for more than 99% of the geomagnetic field. The external magnetic field is mainly composed of the magnetic field superposition, which is generated by the solar activity acting on the atmospheric ionosphere and magnetosphere (Y. Kamide, A. C. L. Chian, in Handbook of the solar-terrestrial environment. J.-L. Jian. Science Press, pp. 91–96, 2010). The geomagnetic field has the following characteristics: (1) It continuous distribution in the near-Earth space; (2) It differences in the geomagnetic field in various regions due to the distribution of the Earth's magnetic materials;(3) It is strong near the ground and gradually decays with the increase of height; (4) The change period of the main magnetic field originating from the Earth's core is measured in centuries, and the change of the anomalous field originating from the Earth's crust is recorded in geological ages, so the main magnetic field and the anomalous field are stable; (5) The changing magnetic field mainly originates from outside the Earth, and the trend of change is consistent within hundreds of kilometers of geography. The geomagnetic field has been widely used for orientation navigation of ships and airplanes, and the geomagnetic field orientation information is measured using compasses and magnetic compasses to obtain a stable north pointing of the Earth (K. Liu, in Research on long-distance geomagnetic navigation based on magnetotactic search. NorthWestern Polytechnical University, pp. 45–50, 2019). Geomagnetic positioning navigation technology, unlike orientation measurement technology, uses the characteristic that the intensity of the geomagnetic field has different distributions with geospatial location to achieve the positioning of the motion platform. Through magnetic field sensors installed on the motion platform, the geomagnetic field data on the motion track is measured in real-time. Features are extracted and matched with the geomagnetic field model or geomagnetic reference map obtained and stored in advance to determine the real-time position of the motion platform (K. Chen et al., in Journal of Zhejiang University-Science A (Applied Physics & Engineering), 22(5):357–368, 2021; Feng-Min et al. in Journal of Projectiles, Rockets, Missiles and Guidance 41:10–14, 2021; G.-G. Wang et al. in A geomagnetic localization method based on road magnetic field characteristics. Beijing: CN107621263B, 2019–12-27; X. Li et al., in Chinese Journal of Sensors and Actuators, 30(12):1869–1875, 2017; Zhuang-Sheng et al. in Progress in Geophysics 26:1473–1477, 2011). Ultimately, a high-precision local three-dimensional spatial reference geomagnetic field that meets the requirements of geomagnetic positioning and navigation can be constructed.