Abstract
The definition of shoreline is not the same for all contexts, and it is often a subjective matter. Various methods exist that are based on the use of different instruments that can determine and highlight a shoreline. In recent years, numerous studies have employed photogrammetric methods, based on different colours, to map the boundary between water and land. These works use images acquired by satellites, drones, or cameras, and differ mainly in terms of resolution. Such methods can identify a shoreline by means of automatic, semi-automatic, or manual procedures. The aim of this work is to find and promote a new and valid beach topography-based algorithm, able to identify the shoreline. We apply the Structure from Motion (SfM) techniques to reconstruct a high-resolution Digital Elevation Model by means of a drone for image acquisition. The algorithm is based on the variation of the topographic beach profile caused by the transition from water to sand. The SfM technique is not efficient when applied to reflecting surfaces like sea water resulting in a very irregular and unnatural profile over the sea. Taking advantage of this fact, the algorithm searches for the point in the space where a beach profile changes from irregular to regular, causing a transition from water to land. The algorithm is promoted by the release of a QGIS v3.x plugin, which allows the easy application and extraction of other shorelines.
Highlights
The monitoring of coastal areas is very important and meaningful to safeguard the benefits that these areas bring to the environment and to the human activities
Shorelines are idealized as the dynamic interface between water and land [1] and, according to Boak and Turner [2], there are two main categories of shoreline indicators: those based on the detection or identification of visible features and those based on the intersection of the coastal profile with a specific elevation datum like the 0m Above Mean Sea Level (AMSL)
The method proposed in this study was found to be a valid alternative to the classical methods of shoreline identification based on topography
Summary
The monitoring of coastal areas is very important and meaningful to safeguard the benefits that these areas bring to the environment and to the human activities. Monitoring starts with the control of the shoreline, which is the line where the land meets the sea. Shorelines are idealized as the dynamic interface between water and land [1] and, according to Boak and Turner [2], there are two main categories of shoreline indicators: those based on the detection or identification of visible features (e.g., instantaneous water lines, vegetation lines) and those based on the intersection of the coastal profile with a specific elevation datum like the 0m Above Mean Sea Level (AMSL). Different methodologies exist for coastal monitoring, which are based on direct and remote acquisition systems. Direct shoreline surveys are normally conducted using the DGPS technique of post-processing or of real-time methodology [3,4]. Remote sensing for the correct positioning of the shoreline can be distinguished by observation of satellite images [5,6,7,8,9], Unmanned Aerial Vehicles (UAV) [10,11,12,13], video monitoring [14,15], historic aerial photos, and cartography [16,17]
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