Radiometric Information from UAS-Borne Close Range Lidar

Christian BRIESE¹ / Martin PFENNIGBAUER² / Michael DONEUS³ / Andreas ULLRICH⁴
(¹Department of Geodesy and Geoinformation, Vienna University of Technology / ²LBI for Archaeological Prospection and Virtual Archaeology, Vienna / ³Department of Prehistoric and Historical Archaeology, University of Vienna, VIAS – Vienna Institute for Archaeological Science, University of Vienna /⁴RIEGL Laser Measurement Systems GmbH, Horn, Austria)

Keywords: radiometric calibration, UAV, UAS, airborne laser scanning, lidar

Abstract:
Airborne laser scanning (ALS) is an active remote sensing technique that is typically used for the acquisition of large landscapes. The resulting three-dimensional point cloud is utilized for a lot of different application areas. Since several years, ALS is also widely used in archaeological prospection. Next to the typically used geometric information, recent publications demonstrate the possibility and first investigations for the practical applicability of calibrated radiometric information from ALS data. Next to ALS sensors designed for different application areas, light weight ALS sensors for unmanned aerial systems (UAS) became available just recently.
This contribution focuses on the radiometric calibration of a data acquired with a new UAS-borne single-wavelength close range ALS sensor, the RIEGL VUX-1. The sensor was tested onboard a standard helicopter on the study site Carnuntum, Austria as there was no adequate UAS System available at the time of data acquisition. After acquisition, the ALS data was radiometrically calibrated with the help of the software OPALS. Subsequently, calibrated reflectance maps at the laser wavelength of 1550 nm are available. These maps can be used in order to study the present archaeological features. Compared to standard passive images these maps are not influenced by the actual illumination by sun light, i.e. there are no shadows, due to the active laser illumination. Additional, the absolute radiometric calibration allows to analyse multi-temporal ALS datasets of the same laser wavelength. Furthermore, the resulting calibrated reflectivity maps at a wavelength of 1550nm might be an interesting reference for the radiometric calibration of airborne passive image spectroscopy data. Finally, a summary and an outlook to future research work conclude the contribution.