Nationwide seagrass mapping using analysis-ready Sentinel-2 and PlanetScope data to support the Nationally Determined Contributions of Seychelles

Kurzfassung

There is a notable lack of spatially-explicit knowledge on seagrass meadows in many parts of the world, which hinders seagrass research, conservation, and carbon accounting efforts. With the recent introduction of the pan-tropical PlanetScope basemaps onto the Google Earth Engine (GEE) cloud platform through the Planet & Norway’s International Climate and Forests Initiative (NICFI), anyone can now freely access and process the entire pan-tropical archive of the PlanetScope between 2015 and today. In comparison to other public optical satellite archives available within GEE, like the Sentinel-2, Planet’s imagery has a shorter global revisit interval of 30.3 h, a better spatial resolution of 4.77m, but a worse spectral resolution of only the blue, green, red and near infrared bands. Despite the NICFI’s focus on terrestrial forest monitoring in the tropics, a vast pan-tropical area of optically shallow coastal waters is included in the cloud-native public archives. This paves the way for high-resolution seamless pan-tropical seagrass mapping with large time and cost efficiency. Here, we adapt our multitemporal composition approach on GEE, initially developed for Sentinel-2, to the six-year PlanetScope archive, to map the nationwide seagrass meadows in Seychelles. We compare the feasibility and performance of the PlanetScope data to Sentinel-2 in national seagrass mapping, leveraging the synergy of cloud computing, artificial intelligence, and open reference data. The development of this approach could and will provide a comprehensive blueprint seagrass mapping and monitoring system to quantify national seagrass blue carbon stocks for the Nationally Determined Contributions, both within and beyond Seychelles.