Iowa physicists find low-cost way to calibrate magnetometers

A University of Iowa research team has identified a less expensive method to calibrate magnetometers, devices that measure magnetic fields.

Triaxial magnetometers, which measure magnetic fields along three axes, are used in GPS, metal detectors, and space and ground-based studies of planetary and solar magnetic fields. If the devices are not properly calibrated, the data they collect can be inaccurate.

Traditionally, to calibrate the devices, researchers must take magnetometers to large coil facilities - laboratories where scientists can observe how the instruments respond to magnetic fields.

These facilities create a precisely controlled magnetic field around the device. Because researchers know the values of the magnetic field they are creating, they can compare that baseline data to the magnetometer's values and adjust accordingly.

Jessica Mondoskin, a graduate student in the Department of Physics and Astronomy and the study's first author, says calibrating triaxial magnetometers is expensive, and access to professional testing facilities is limited. That can make it difficult for citizen scientists and educators to properly calibrate the instruments themselves.

Mondoskin found a way around that. In an open field, her team rotated a magnetometer in every possible orientation while keeping it as still as possible, helping the device calibrate itself using Earth's magnetic field.

Her team demonstrated that anyone with access to an open field away from cars, buildings, and other sources of magnetic disturbance can properly calibrate a magnetometer.

Mondoskin said that using the method, paired with a computer-generated map of Earth's magnetic field, calibration was approximately one-third of 1% off from the expected magnetic field present around the device.

It's a margin of error small enough to make the new method viable for a range of research activities, such as tracking magnetic field changes during an aurora or studying geomagnetic disturbances during a solar eclipse.

Mondoskin hopes her triaxial magnetometer calibration technique will lead to greater availability of low-cost magnetometers and a greater understanding of magnetic fields.

"Magnetic fields are one of those amorphous things that can be difficult to grasp, especially when you're younger and you're told that there's an invisible field in the sky," she says. "Having more hands-on opportunities to observe it will be really beneficial for scientists of all ages and backgrounds."

The study, "Determining an Error Budget for a Low-Cost Method of Vector Magnetometer Calibration Using a Variety of Scalar Magnetic References," was published online July 8 in the journal Frontiers in Astronomy and Space Sciences.

David Miles, associate professor in the Department of Physics and Astronomy at Iowa, is a study co-author. Other authors include Matthew Finley, an assistant research scientist at Iowa; Alex P. Hoffmann, Hyunju Connor, and Andrew Mentges, from NASA Goddard Space Flight Center; Miguel Martinez-Ledesma, from Catholic University of America; and Katya Sanamyan, a student at Walter Johnson High School through NASA Goddard Space Flight Center's Academic Research Experience Program.

The work was funded by NASA and the Space Weather Underground project based in Greenbelt, Maryland.