Recognizing Geomagnetic Storms in Marine Magnetometer Data: Toward Improved Archaeological Resource Identification Practices

Abstract Strong magnetic field perturbations resulting from Earth-directed solar events, collectively referred to as geomagnetic storms, can adversely affect many aspects of marine archaeological survey. The immediate onset of geomagnetic storms and the fast compression of the magnetopause creates a short-duration, high amplitude spike in Earth’s magnetic field that appears similar to the signature of an archaeological anomaly. Aggressive processing, analysis, and comparison of single instrument, total field marine magnetometer survey and observatory datasets collected during geomagnetic storms on days of Kp 5 or greater resulted in no demonstrable ability to isolate and remove the storm sudden onset signature. Of the 34 storms analyzed, 34 possessed onset signatures that were considered to be potentially misleading, resulting in possible aliasing of temporal variation (the storm sudden onset signature) for spatial variation (archaeological anomalies of interest). Based on a 95% confidence level, it is estimated that 89.7 to 100 percent of geomagnetic storms occurring on days of Kp 5 or greater will generate signatures that may be misinterpreted as archaeological sites. Recommendations are made for marine magnetic data collection and processing methods that may adequately account for geomagnetic storms, allowing for improved precision in analytical interpretation and thus improved management of archaeological resources.