CROWDMAG AS AN INTRODUCTION TO GEOPHYSICAL DATA COLLECTION AND ANALYSIS

The NOAA/CIRES CrowdMag app allows citizen scientists to collect magnetic field data using the 3-component magnetometers built in to all modern smartphones. The 17K+ worldwide users of the app provide crowd-sourced regional measurements of the Earth’s magnetic field in support of global field models. For example, the NOAA/CIRES geomagnetism team produces the World Magnetic Model (WMM), the official military spec model (degree and order 12) used by the US Government and embedded in virtually every smartphone (to make declination corrections for digital compass orientation).

The CrowdMag app also has great potential as a teaching and learning tool. The app allows users to collect magnetic data values “in the field” – for example, on walking or bicycling traverses. Data are collected at discrete points as selected by the user, then are sent via email to the users as an ASCII CSV file (appropriate for input directly into Microsoft Excel, for example). The user can analyze their own data to learn about signal-to-noise evaluation and about variations in the magnetic field caused by both natural and man-made objects.

One of us (Anjelique) led a “CrowdMag Day” exercise at the University of Colorado this summer (July 2017) as part of a summer internship program. The exercise involved organizing teams of fellow interns to walk a common traverse along bike paths in east Boulder. Analysis of the synchronous records from multiple phones gives insight into the data stability of individual phones (they are noisy at the 500 nT level) and the amplitude and scale of magnetic anomalies associated with some types of urban infrastructure, specifically bridges, overpasses, underpasses and intersections (anomalies of >5000 nT are not unusual).

Additional educational applications of CrowdMag include other types of local magnetic anomaly mapping (indoors, outdoors, traverse or grid), hunting for interesting magnetic features (either natural or man-made), and further signal-to-noise and/or validation experiments. Students can also use the app simply to introduce others to the unseen magnetic world around us.