Cloud‐native seascape mapping of Mozambique’s Quirimbas National Park with Sentinel‐2

Abstract

Abstract The lack of detailed spatial information on coastal resources, notably shallow water coral reefs and associated benthic habitats, impedes our ability to protect and manage them in the face of global climate change and anthropogenic impacts. Here, we develop a semi‐automated workflow in the cloud that uses freely available Sentinel‐2 data from the European Space Agency (ESA) Copernicus programme to derive information on near‐shore coral reef habitats in the Quirimbas National Park (QNP), a recently declared biosphere reserve in northern Mozambique. We use an end‐to‐end cloud‐based framework within the Google Earth Engine cloud geospatial platform to process imagery from raw pixels to cloud‐free composites which are corrected for glint and surface artefacts, water column and derived estimated depth and then classified into four benthic habitats. Using independent training and validation data, we apply three supervised classification algorithms: random forests (RF), support vector machine (SVM) and classification and regression trees (CART). Our results show that random forests are the most accurate supervised algorithm with over 82% overall accuracy. We mapped over 105 000 ha of shallow water habitat inside the protected area, of which 18% are dominated by coral and hardbottom; 27.5% are seagrass and submerged aquatic vegetation and another 23.4% are soft and sandy substrates, and the remaining area is optically deep water. We employ satellite‐derived bathymetry to assess slope, bathymetric position, rugosity and underwater topography of these habitats. Finally, a spectral unmixing model provides further sub‐pixel–level information of habitats with the potential to monitor changes over time. This effort provides the first, consistent and repeatable and also scalable coastal information system for an east African tropical marine protected area, which hosts shallow‐water ecosystems which are of great significance to local communities and building resilience towards climate change.

Keywords

• Seascapes
• Seagrasses
• Corals
• Earth Observation
• Google Earth Engine
• Sentinel‐2