Abstract
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.
Highlights
There are numerous methods employed for measuring natural rates of change on rock surfaces
For decades researchers were restricted to direct measurement of change relative to a datum; this method has been largely superseded by techniques which fall into two general categories: contact methods which utilize erosion meters and non-contact methods such as terrestrial laser scanning (TLS) and structure from motion (SfM) photogrammetry (Moses et al, 2014)
Measurements of micro-scale platform erosion using a transversing micro-erosion meter (TMEM) are limited to repeated point measurements over time, which provides a mean rate of surface downwearing within the measurement area for that measurement period with the dominant process(es) being inferred from the spatial and temporal variation in downwearing rates (Trenhaile, 2003)
Summary
There are numerous methods employed for measuring natural rates of change on rock surfaces. For decades researchers were restricted to direct measurement of change relative to a datum; this method has been largely superseded by techniques which fall into two general categories: contact methods which utilize erosion meters and non-contact methods such as terrestrial laser scanning (TLS) and structure from motion (SfM) photogrammetry (Moses et al, 2014). The micro-erosion meter (MEM) and its successor the transversing micro-erosion meter (TMEM) are the most frequently applied instruments for quantifying microscale erosion. SfM photogrammetry is fast emerging as a valuable tool for detecting and quantifying geomorphic change across a range of scales and environments and represents a potential alternative to the MEM and TMEM for measuring erosion on shore platforms if a suitable level of resolution, accuracy, and repeatability can be achieved. A brief overview of the two methods is given below
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