Robust aerial navigation without GPS is a challenging problem. Alternative navigation systems for airborne use are often limited by where and when they can operate. For example, terrain following systems cannot operate over oceans, and star-tracker and computer-vision systems depend on weather and daylight. Navigation using the Earth's magnetic anomaly field, which is globally available at all times, shows promise to overcome many of these limitations. We designed an airborne navigation system that utilizes only passive instruments—an optically pumped scalar magnetometer, an inertial navigation system (INS), a barometer, and a magnetic anomaly map. The navigation system uses a particle filter to correct errors in an INS as well as estimate measurement-corrupting temporal variations by comparing actual magnetometer measurements to expected measurements from the magnetic anomaly map. A complete measurement equation is presented that describes the nontrivial relationship between the real-time magnetometer measurements and the magnetic anomaly map. We validated the navigation system with real data from a flight test over Louisa, VA. Horizontal DRMS errors of 13 m were achieved over an hour long flight at the map altitude of 1000-ft MSL using a magnetic anomaly map created 3 years ago. This result should be considered as a “best case” result when using the presented methods, since the flight test was conducted in ideal conditions. The demonstrated accuracy of the navigation system shows orders of magnitude improvement over previously published magnetic navigation experimental results, indicating that the magnetic anomaly navigation is a promising addition to current global positioning system alternative and backup systems.
['Aaron J. Canciani', 'John F. Raquet']
Airborne Magnetic Anomaly Navigation