Remotely sensed mapping of the intertidal zone: A Sentinel-2 and Google Earth Engine methodology

Abstract

The coasts of the United Kingdom and the Republic of Ireland support a variety of tidal ranges with intertidal zones that can cover large areas and span several shoreline types. There has been an increased recognition of the ecosystem system services derived from the intertidal zone, however, evidence also suggests an overall reduction in intertidal extents since at least 1945. The intertidal zone has proven to be a difficult environment to regularly survey and map at national scales in many countries due to high cost and logistical complexities, so a new approach that is accurate, rapid, cost-effective and easily updated would provide a powerful tool for coastal zone management. An approach to map the intertidal zone by measuring water occurrence frequencies using tidally calibrated satellite imagery (Sentinel-2), and processed within Google Earth Engine (GEE), is proposed here as a complimentary approach to support traditional aerial or ground surveying. Using the United Kingdom and the Republic of Ireland as a test case, the resulting output, termed Coast X-Ray, compares favourably with the outputs from high-resolution digital elevation model datasets. Coast X-Ray provides an up-to-date insight into the morphology of the intertidal zone across the United Kingdom and the Republic of Ireland and can be used by a range of stakeholders to support coastal management and high-level coastal change assessments.