A Simplified Close‐Range Photogrammetric Technique for Soil Erosion Assessment

Abstract

Surface reconstruction using digital photogrammetry offers a great advantage for soil erosion research. The technology can be cumbersome for field application because it relies on the accurate measurement of control points, often using a survey‐grade instrument. Also, even though digital photogrammetry has been used in much soil erosion research, its sensitivity in detecting soil elevation changes has rarely been assessed. This study aimed at simplifying the digital photogrammetric procedure for soil erosion research and assessing the sensitivity of this technology to detect soil erosion. To simplify the technology, we propose to combine a photogrammetric procedure for control point generation in a first step, followed by a conventional photogrammetric digital elevation model (DEM) extraction procedure. The performance of the method was assessed in the laboratory and tested in the field to digitize ephemeral gullies. In the accuracy test of photogrammetric survey step, we found that the maximum length measurement error was 3.4 mm, while the maximum angular deviation from the vertical or horizontal axes was 0.93°. The maximum error between control point coordinates generated by photogrammetry and those generated by a survey‐grade total station was 26 mm on the horizontal axes and 10 mm on the vertical axis. We also found that the sensitivity of digital photogrammetry in detecting soil surface elevation changes was similar to that of a laser scanner when the detection was performed on smooth soil surfaces and when the standard deviation of the elevation changes was approximately three times the precision of the photogrammetric DEM.