Crustal deformation detection using close-range photogrammetry

The objective of this study is to perform high temporal frequency crustal deformation monitoring using close-range photogrammetric technique, which has high accuracy and spatial resolution, to distinguish small relative displacement caused by the movement of fault. For this purpose, we propose the use of coded targets and man-made permanent white round targets through close-range photo triangulation software that is capable of automatic recognition and referencing. The test site is located near Guanshan Township in eastern Taiwan where a significant rupture on the concrete wall of a drainage channel is caused by the movement of Chihshang creeping fault. We equally spread and fixed 786 round white targets on the wall using stainless nails and measure their coordinates every month. A DSLR camera with fixed focal length lens (20mm) is adopted in order to maintain the stability of its internal geometry. During image acquisition, a convergent imaging scheme is essential in order to obtain strong imaging geometry with best positional accuracy. For each data acquisition period, a set of three-dimensional coordinates for all round white targets were obtained. Comparing with two different periods, we may evaluate the relative displacement of all targets by selecting several targets located on one side of the crack as control points through conformal transformation. Experimental results show that the proposed scheme can obtain reliable results and recognize the relative displacement caused by the movement of fault.