MagSLAM: Aerial simultaneous localization and mapping using Earth's magnetic anomaly field

Abstract

Instances of Global Positioning System (GPS) jamming and spoofing have identified the vulnerabilities of using GPS as a sole means of positioning, navigation, and timing (PNT) for the world’s critical systems. A fusion of alternative positioning methods is necessary to replace the characteristics of GPS the world has become reliant upon. Aerial navigation using magnetic field crustal anomalies is a globally available, passively sensed, and nearly unjammable GPS-alternative positioning method. The Earth’s outer core produces a magnetic field which is perturbed by magnetically susceptible materials in the Earth’s crust. The resulting deviation from a core field reference model is a world-wide magnetic anomaly field shown to be a viable signal for navigation. This method required prior-surveyed magnetic anomaly maps of sufficient quality. Aerial geomagnetic surveys require more grid lines to fully sample the higher spatial variation of the magnetic anomaly field at low altitudes. This makes producing high-quality low-altitude magnetic maps expensive and therefore less common. The miniaturization of scalar magnetometers opened the potential for magnetic navigation on low-flying unmanned aerial vehicles (UAVs), which operate at altitudes lacking high quality magnetic maps. This motivated a method to remove magnetic navigation’s dependency on a magnetic map. Indoor robotic and pedestrian magnetic navigation have employed simultaneous localization and mapping (SLAM) techniques to overcome this obstacle. This research extends SLAM concepts to eliminate the map dependency in aerial magnetic navigation. This research presents three main contributions. An aerial magnetic SLAM filter was designed which constrained the drift of an aircraft’s inertial navigation system (INS) on a real flight-test dataset from 1 kilometer to tens of meters over a 100 minute flight without a prior magnetic iv map. A commercial off-the-shelf (COTS) fixed-wing magnetic surveying UAV was configured and produced six consistent magnetic maps at various altitudes over a 2 kilometer area. The UAV’s magnetic measurements were used to constrain three simulated INS grades to tens of meters over a 14 minute flight. Together, these three contributions demonstrated the viability of aerial magnetic navigation as a GPS alternative for manned aircraft and UAVs without requiring prior-surveyed magnetic maps.