UAS aeromagnetic survey and hyperspectral data for mineral exploration

Geophysical methods for mineral exploration require cost- and time-effective ways to acquire high resolution data to supplement field mapping. During the last few years, lightweight magnetometers and hyperspectral imaging (HSI) sensors have been increasingly and independently developed for their use on unmanned aerial systems (UAS). We propose that the combination of hyperspectral images and UAS aeromagnetic surveys can provide a rapid and cost-effective technology to improve the detection of shallow targets and to delineate mineral structures in potentially hazardous terrains where traditional techniques cannot be operated safely. With low altitude flights and tight flight lines, UAS aeromagnetic surveys can help overcome the scale gap between ground and air-borne magnetics and deliver high resolution maps. However, data corrections are required for UAS aeromagnetic data to achieve valid observations and reliable maps. For this study the main magnetic compensations applied to the magnetics were meant to attenuate temporal variations, headings and maneuvering errors. The interpretation of accurate total field maps can be improved with the aid of hyperspectral images. HSI are widely used in geological mapping and mineral exploration (e.g., van der Meer et al., 2012, Jakob et al., 2016). A comprehensive data set including hyperspectral images and handheld spectral measurements of the study area in Siilinjärvi, Finland, was acquired before the UAS aeromagnetic survey was performed. The UAS magnetics was acquired at 40 m height, with a line spacing of 20 m, covering an area of 3.894 ha.
Data processing of the UAS aeromagnetic data revealed the importance of making appropriate corrections for the reliability of the total magnetic intensity (TMI) and derived maps. Results suggest that UAS aeromagnetic data captured the main geological trends of the area by applying pertinent corrections. Aided by the HSI information, the sources of the magnetic anomalies were identified. A high magnetic contrast created by a syenite intrusion located in a glimmeritic carbonatite complex is consistently delineated by the UAS aeromagnetic data. Outcropping areas of the syenite intrusion can also be identified in the available hyperspectral image of Siilinjärvi.