A tool to extract coastlines and shore buffer zones using satellite imagery and Google Earth Engine

Assessment of shoreline evolution is key for many coastal management and practical applications. Coastal zones are dynamic by nature, with this dynamism subject to numerous studies often focusing on the identification of ‘coastlines’/’shorelines’. Where this coastline (or shoreline) location is, and how it changes, is a fundamental variable in understanding coastal environments. For example, beaches are highly mobile and their interaction with coastal dunes has been key for the development of classical conceptual models. A number of remote sensing methods and algorithms have been designed to extract instantaneous coastlines from satellite imagery. These represent a snapshot of the position of the coastline at a particular time. However, coastlines do not exist over a time period, as they dissolve in a ‘buffer zone’, an interphase between land and ocean where water and sand are constantly mixing. This buffer zone can vary in size depending on the location and the time of the year. Drawing on the experience gathered by the use of variance images from Argus video monitoring systems, we present an alternative approach for coastline and shore buffer zone detection using medium resolution satellite imagery and Google Earth Engine. This method takes advantage of the increasing availability of satellite data and focuses on collections of satellite images acquired over time periods, instead of single-date images. It aims to minimise user input by applying image compositing and segmentation, with shore buffer zones identified using variance image composites. The approach is tested in beaches with diverse hydro and morphodynamic characteristics. This method obtains medium to long term information of coastal dynamics including average coastline locations and extent of shore buffer zones.