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Abstract
Measuring beach topography accurately and with high spatial resolution is an important aspect of coastal management and is crucial for understanding changes in beach morphology, especially along complex, three-dimensional shorelines. Traditional methods of beach surveying even at high resolution are insufficient to measure the complex, dynamic behavior along these coasts. This study investigates the optimization of Unmanned Aerial Systems Structure from Motion (UAS-SfM) data acquisition methodology with regard to flight altitude and the configuration and amount of ground control points (GCPs). A sensitivity analysis was performed to determine the UAS and GCP characteristics that produce the most accurate digital elevation model (DEM). First, an evaluation of the UAS-SfM technique was performed and proved advantageous over traditional surveying techniques with regard to efficiency, automation, ease of use, and repeatability. The results of the sensitivity analysis showed the highest (116 m) flight altitude evaluated was the most accurate and required the least amount of survey and processing time. The optimal configuration of GCPs was determined to be (1) in the corners of the study site, (2) at high and low elevations within the study site, and (3) with sufficient cross-shore and alongshore coverage. Finally, it was found that 15 GCPs produced the best results, but that as few as 11 GCPs could be used without any significant loss in accuracy. It was also observed that fewer (≈7–9) well-placed GCPs in the optimal configuration produced the same magnitude of error as using more (15) poorly placed GCPs. Based on these results, a set of recommendations for conducting UAS-SfM surveys along complex, three-dimensional, developed coastlines is presented.
Highlights
The quantification of beach topography is important for understanding morphological evolution, monitoring beach nourishment projects, assessing storm-induced sediment transport, calculating rates of change, and more [1]
21 ground control points (GCPs) targets were distributed throughout the dry beach area of 0.12 km2, and the total survey area of 0.25 km2 remained fixed for each flight
The study described in this paper was conducted to highlight and quantify the advantages of UAS to measure coastal morphology on a developed highly complex 3D beach, and to find the optimal UAS and GCP parameters to produce the most accurate and efficient results
Summary
The quantification of beach topography is important for understanding morphological evolution, monitoring beach nourishment projects, assessing storm-induced sediment transport, calculating rates of change, and more [1]. It is widely recognized as being significant, as beaches have direct and indirect impacts on ecosystems, the economy, recreation, and a wide variety of professions and lifestyles. The most commonly used or ‘traditional’ method of measuring beach survey cross-shore beach cross-shore profiles spanning thespanning dune or upland area to the a topography is to survey beach from profiles from the dune or swash uplandzone areausing to the real-time kinematic positioning system Receiver is attached swash zone using aglobal real-time kinematic global positioning system the GPS).
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