Digital close range photogrammetry for the study of rill development at flume scale Minghang Guo a , Haijing Shi a, ⁎, Jun Zhao a , Puling Liu a , Dustin Welbourne b , Qi Lin c a State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Northwest A&F University, Yangling 712100, Shaanxi, China b School of Physical, Environmental and Mathematical Sciences, University of New South Wales, Canberra, ACT, 2600, Australia c Xi'an Dunrui Surveying Technology Co. Ltd., Xi'an, Shaanxi 710065, China abstract article info Article history: Received 13 April 2015 Received in revised form 2 March 2016 Accepted 28 March 2016 Available online 27 April 2016 Soil erosion is a continuous process of detachment, transportation, and deposition of soil particles. Obtaining ac- curate descriptions of soil surface topography is crucial for quantifying changes to the soil surface during erosion processes. The objective of this study was to develop an improved close-range photogrammetric technique to as- sess soil erosion under rainfall conditions. Based on high overlapping image acquisition, digital point cloud matching, digital elevation model (DEM) generation and soil erosion calculation, a digital close-range photo- grammetric observation system was explored and established. The results showed that the established digital photogrammetric observation system could accurately calculate the digital point cloud from the underlying sur- face with a 2 min time interval and a 1.5 mm spatial resolution. In addition, based on the DEM generated from digital point clouds, the amount of soil erosion in different topographic positions within various time periods was calculated. The digital photogrammetric observation methods explored in our study provide a reliable way to monitor soil erosion processes, especially under rainfall conditions. This approach can accurately resolve the evolution of the underlying surface soil erosion, which is of great importance in understanding soil erosion mechanisms. © 2016 Elsevier B.V. All rights reserved. Keywords: Soil erosion Digital elevation model Digital photogrammetric observation Digital point cloud Observation method 1. Introduction Soil erosion is an important environmental issue in many parts of the world. Detachment and transportation of soil particles during the ero- sion process can result in soil degradation, water pollution and damage to drainage networks (Morgan, 2005; Peter Heng et al., 2010). During an erosion event, the soil surface is continuously transforming. Depending on the volume of soil transported, erosion processes can result in con- siderable topographic variations that can have broad effects on agricul- tural practices (Liu et al., 2004; Peter Heng et al., 2010). Various technologies have been developed by soil and geomorphology scientists to acquire detailed information on the variation in the soil surface caused by erosion (Nouwakpo and Huang, 2012). Contact techniques, such as the erosion pin and rillmeter, have long been used to understand changes in the soil surface during erosion (Elliot et al., 1997; Kronvang et al., 2012). Although the change in the length of the exposed part of the pin can be used to calculate the amount of erosion that has occurred after an erosion event, the accuracy of the erosion pin technique is limited by the low spatial coverage due to the small number of pins (Sirvent et al., 1997; Zhang et al., 2011). The rillmeter technique can acquire precise data for the measurements of soil surface geometry, but it can disturb the soil surface during the mea- surement process due to the contact between the rillmeter device and the soil surface (Elliot et al., 1997). As technology has become more robust and accessible in recent years, non-contact soil surface tech- niques, such as laser scanning and digital close-range photogrammetry, have been adopted to overcome the limitations of contact methods (Babault et al., 2004; Nouwakpo and Huang, 2012). Both laser scanning and digital close-range photogrammetric tech- niques have been widely used to generate DEMs with sufficient resolu- tion for micro-topographic analysis (Aguilar et al., 2009; Babault et al., 2004; Nouwakpo and Huang, 2012; Rieke-Zapp and Nearing, 2005). Comparatively, digital photogrammetry allows for faster data acquisi- tion and a wider vertical range of the DEM (Aguilar et al., 2009; Rieke-Zapp and Nearing, 2005). In addition, a camera is easier to handle, and a digital photogrammetric system allows operators to scale accord- ing to their own requirements (Frankl et al., 2015; Rieke-Zapp et al., 2001). Therefore, digital photogrammetry enables the possibility of instantaneous data capture. Previous investigations have proved the usefulness of high- resolution digital close-range photogrammetry in soil erosion studies. The experimental plots in those studies varied between 0.09 and 16 m 2 , and the grid resolution of generated DEMs ranged from 1 to 15 mm (Abd Elbasit et al., 2009; Aguilar et al., 2009; Brasington and Smart, 2003; Peter Heng et al., 2010; Rieke-Zapp and Nearing, 2005). Catena 143 (2016) 265–274 ⁎ Corresponding author. E-mail address: shihaijingcn@126.com (H. Shi). http://dx.doi.org/10.1016/j.catena.2016.03.036 0341-8162/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Catena journal homepage: www.elsevier.com/locate/catena