Applying close-range photogrammetry to monitor the crustal deformation

Close-range photogrammetry is a low-cost, efficient and accurate method that can take photos in a short distance. It has been applied to high accuracy 3D modeling, object recognition, and deformation monitoring. In this study, a consumer grade digital camera, artificial coded targets and permanent nails are adopted to monitor the displacement on a drainage channel, where a significant rupture surface caused by the Chihshang creeping fault can be observed. The coded targets can be automatic detected and perform fully-automatic photo-triangulation, and assist the computation of the permanent nail's coordinates. To monitor the displacement, we equally fixed 786 stainless nails in 5 rows by 160 columns on the wall surface as permanent targets and measure their coordinates by the close-range photogrammetry every few months. After obtaining the 3D coordinates of permanent targets in different periods, we can evaluate their relative displacement through the method using seven-parameter transformation (3D conformal transformation) that transferring the coordinates system of later period to previous one. In order to evaluate the accuracy and the minimum detectable relative displacements, an experimental field is thus established on a building facade by manually move several coded targets. Experimental results show that the proposed approach can detect 1 mm displacement proving the proposed scheme can be applied in-situ to monitor the crustal deformation. The results of in-situ data collected within 2years period shows that the maximum displacement of 20 mm was detected near the rupture surface.