Ch 48. Positioning Using Magnetic Fields

Overview

Navigation using Earth’s magnetic field is one of the oldest forms of navigation. For nearly a thousand years humans have observed that a compass needle points north, and have used this fact to navigate their world. An understanding of magnetic fields came long after the compass became an accepted navigational tool. Today, the use of magnetic fields in navigation is seeing renewed interest, particularly for determining absolute position rather than just orientation. Unlike the determination of orientation, determining position using the magnetic field relies on being able to match measured variations in the magnetic field to a map of these variations. In that sense, it is a form of map matching and has proved its usefulness for navigating in challenging environments, providing both relative and absolute positioning information in many distinct environments.

Magnetic fields are three‐dimensional vector fields created by magnetic materials or electric currents. A navigation system may use the both the measured direction and intensity of this vector field as a navigation signal. Historically, Earth’s core magnetic field was the main source of navigation information. As technology has improved, other magnetic sources (or variations in Earth’s magnetic field) have proved to be useful navigation signals.

This chapter will describe approaches for determining absolute position using magnetic field measurements for three different environments: indoors, for ground vehicles, and for aircraft. However, before describing these approaches, it is necessary to provide some background in terms of the nature of Earth’s magnetic field (Section 48.2) and describe magnetic field sensors and how they are characterized and calibrated (Section 48.3).