Differences between terrestrial and airborne SFM an d MVS photogrammetry applied for change detection within a sinkhole in Thuringia, Germany

Structure from motion (SFM) combined with multi vi ew stereo (MVS) reconstruction is a cost effective met hod to assess topographic change, to analyse long term developmen t and to perform risk assessments. The objective of this stu dy was the comparison of two image acquisition methods, terres trial handheld and UAV based photography regarding the detectable changes over time and the differences between the point clouds o f the ‘Äbtissingrube’ – a sinkhole in Thuringia, Germany. The imagery was taken yearly from 2017 to 2019 with both UAV an d handheld camera. The 3D point clouds were processed within A gisoft PhotoScan Pro. Additionally the point precisions we re estimated with SFM_Georef and the differences in the resulting point clouds were compared using multiscale model to model cloud comparison with precision maps (M3C2-PM) in CloudCompare. The resulting differences are 10.2 percent of detectable change b tween the 2019 UAV and terrestrial point cloud with a mean detectable change of 9.0 mm. Change detection from 2017 to 2019 shows 61 .1 percent of detectable change and a mean detectable change of 5 9.6 mm within the sinkhole. The resulting coverage of the sinkhol e was generally higher by the point clouds derived from UAV in comparison to the handheld camera.