GRSG Conference 2022: Orbit to Outcrop
Title: Let the exploration begin: helicopter-borne remote sensing a new addition to geological mapping studies
Author: Sara Salehi
Remote-sensing techniques play an important role in the geological surveys for mapping and mineral prospecting and are particularly well adapted for the investigation of remote and inaccessible areas, either for preparing field work or for supporting thematic mapping in the field.
Satellite images allow for the discrimination of rock units in the broader region and help in effectively defining the best initial targets for regional exploration. Unmanned aerial systems (UAS) are particularly attractive to investigate potential deposits in difficult or environmentally sensitive areas but are limited to small-to-medium-sized survey areas, i.e. tens of square kilometers.
Using a fixed-wing aircraft or helicopter, aerial surveys can provide information in a rapid, non-invasive manner on areas conducive to mineralization that may be otherwise difficult to access from the ground. Fixed-wing aircrafts are useful for large-scale and/or lower-resolution surveys, while helicopter surveys are excellent for defining smaller to medium sized targets at higher resolution and can be flown at both lower ground clearance and speed in terrains that would be impossible to follow in a fixed-wing aircraft.
To address scaling issues and the accessibility in the field, and to provide low altitude data from targets identified using space-borne dataset a helicopter has been utilized as a versatile means of acquiring remote sensing data emphasizing both spatial and spectral information domains using a novel sensors system setup. The focus lies hereby on the integration of digital photogrammetry with helicopter-borne hyperspectral imaging to gather high-resolution geometric data as well as quantitative information about mineral variations in the outcrop. The method is tested in North-East Greenland, where stereo images and hyperspectral data cubes have been collected simultaneously and from both nadir and off-nadir viewing angles.
The highly variable terrain leads to strong illumination and atmospheric absorption variations which must be accounted for in the hyperspectral data processing. A precondition for such correction is an accurate geo-rectification which is done by the PARGE® software. Retrieving the unbiased ground reflectance is solved by a physical based atmospheric correction with the DROACOR® model. The study demonstrates the potential of using helicopters to help understanding the geology in poorly accessible areas and to provide information that may help in the future exploration and geological mapping activities.