Summary
As part of an NGU-funded project led by V. Baranwal, a drone-based aeromagnetic survey was conducted in three areas around Sortland (Vesterålen, northern Norway) to produce high-resolution magnetic maps of known magnetic lows associated with graphite deposits. This region has a historical significance in graphite production and is still known for manufacturing pencils. This report outlines the acquisition, processing, and visualization of the datasets collected during the survey, presenting the results in the form of detailed maps. The three geophysical surveys covered a total area of 10 km², comprising 114, 170, and 152 flight lines, respectively and were conducted in July 2024. The first area was fully surveyed, but the second and third were smaller than anticipated due to a mechanical failure of the drone, which caused two consecutive crashes. The NGU employed a DJI M300 multipurpose drone equipped with a Sensys MagDrone R3, a three-component fluxgate magnetometer securely mounted to the drone’s landing gear. With a sampling rate of 200 Hz and a sensitivity of 150 pT, the magnetometer is optimized for detecting weak magnetic anomalies, making it ideal for this high-resolution geophysical survey. The system weighs only 1 kg, enabling easy integration with the drone. The surveys were conducted at a flight speed of 5 m/s, with a route spacing of 30 meters. The distance between parallel flight lines was adjusted according to the altitude during data acquisition. UGcS software was used for topographic draping, allowing the drone to maintain a constant altitude of 35 meters above ground level. This altitude was selected to ensure clearance from the tallest trees and to accommodate the steep terrain. A total of 75 flights were required to cover the three areas. On the second day of surveying, the drone had a hard landing due to a mechanical issue, though it remained functional, allowing the survey to continue as planned. However, it crashed again one week later, forcing an early termination of the survey. The raw magnetic data were processed using proprietary software, which compensates for the drone’s magnetic interference and generates a clean magnetic dataset. Custom codes were used for data processing, and the results were gridded and visualized using GMT software. Topographic data with a 10-meter resolution were sourced from the Hoydedata.no website.
