A comparison of structure from motion photogrammetry and the traversing micro-erosion meter for measuring erosion on shore platforms

Abstract

For decades researchers have used the micro-erosion meter and its successor the traversing micro-erosion meter to measure micro-scale rates of vertical erosion (downwearing) on shore platforms. Difficulties with “upscaling” of micro-scale field data in order to explain long-term platform evolution have led to calls to introduce other methods which allow for the measurement of platform erosion at different scales. Structure from motion photogrammetry is fast emerging as a reliable, cost-effective tool for geomorphic change detection, providing a valuable means for detecting micro-scale to mesoscale geomorphic change over different terrain types. Here we present the results of an experiment in which we test the efficacy of structure from motion photogrammetry for measuring change on shore platforms due to different erosion processes (sweeping abrasion, scratching, and percussion). Key to this approach is the development of the coordinate reference system used to reference and scale the models, which can be easily deployed in the field. Experiments were carried out on three simulated platform surfaces with low to high relative rugosity to assess the influence of surface roughness. We find that structure from motion photogrammetry can be used to reliably detect micro-scale (sub-millimetre) and mesoscale (cm) erosion on shore platforms with a low rugosity index. As topographic complexity increases, the scale of detection is reduced. We also provide a detailed comparison of the two methods across a range of categories including cost, data collection, analysis, and output. We find that structure from motion offers several advantages over the micro-erosion meter, most notably the ability to detect and measure the erosion of shore platforms at different scales.