The Advanced Navigation Technology (ANT) Center at the Air Force Institute of Technology has been focusing significant effort on solving the problem of how to navigate when GPS is not available, such as indoors or in the presence of GPS jamming. Anything that changes with position is a potential measurement source.
Recently, Capt. Will Storms completed a project involving the use of magnetic field variations within a building for the purpose of navigation. The Earth’s magnetic field is fairly consistent and has been used for years to help orient people or systems to north (or south). However, the magnetic field is modified by metal and other materials that are commonly present in buildings. While these local magnetic field variations make magnetic compasses useless for directional navigation in an indoor environment, these same variations can be used to determine a position indoors. It has been said that “One person’s error is another person’s measurement,” and this is most certainly true in this case. Capt. Storms’ approach can be applied to UAVs flying in a city environment, enabling them to continue to navigate even if GPS is denied due to jamming or signal blockage from buildings.
The fundamental approach that Capt. Storms used was to measure the three dimensional magnetic field using a three-axis magnetometer—a relatively small and inexpensive device slightly smaller than a computer mouse. He developed a method to determine position by comparing the magnetometer measurements with a map of the magnetic field.
When this project began, it was unclear that a reasonable position solution would even be possible. However, the results were significantly better than expected. In a proof-of-concept demonstration using real magnetometers, Capt. Storms demonstrated that his approach was able to determine a vehicle’s position to well within 1 meter accuracy.
The next question Capt. Storms sought to answer was whether or not magnetic field sensors could act as a sort of “electronic breadcrumb” which would enable one vehicle to follow the path where a previous vehicle had gone. The first vehicle would measure the magnetic field variations along its path and send that information back to the trail vehicle. Capt Storms demonstrated that the trail vehicle was able to follow the same path as the lead vehicle using this approach.
Capt. Storms’ outstanding research was recognized when he was awarded the “AFIT Navigation Research Excellence Award,” which recognizes the author of the thesis which is judged to make the most significant research contributions in a navigation-related field. The award, sponsored by the Dayton Section of the Institute of Navigation, consisted of an automobile GPS receiver and a $3000 U.S. Savings Bond.
Based upon these very positive early results, the ANT Center plans to continue magnetic field navigation research. Initially, several summer interns will work at developing a more complete magnetic field variation map and help to determine how much this map changes due to variety of factors, such as doors opening or closing or lights being turned on and off. If this research continues to be successful, it is anticipated that this technology will be used in future autonomous vehicles which will then be able to operate in GPS-denied environments.
