New perspectives for the observation of coastal zones with the Coastal Thematic Exploitation Platform

The coastal environment is a challenging area for Earth Observation because it is at the limit of two very heterogeneous domains. For instance, Ocean Colour data are more difficult to obtain near the coast, as the observed reflectances are affected by the presence of bright sediments, complex aerosol mixtures, as well as stray light from bright land surfaces. Coastal satellite altimetry is also challenging because the proximity of the land affects radar and microwave radiometry measurements. Surface temperature measurements are similarly impacted at the boundary between the land and the sea. On the other hand, in-situ data is easier to access than in the open ocean, and this can help scientists to improve retrieval algorithms. The Coastal Thematic Exploitation Platform (CTEP) is an on-going ESA project to develop a web-service dedicated to the observation of the coastal environment to support management and monitoring; this paper explains how the innovations of the CTEP will provide new means to handle the aforementioned technical challenges and contribute to improved understanding and decision-making with respect to coastal resources and environments. The coastline is an object which naturally calls for a multi-resolution approach. While interactions with the open ocean need to be studied at a large scale, exchanges with rivers and shores need to be tackled at high resolution. When studying water constituents and bio-optical properties, the medium resolution images of OLCI on Sentinel-3 are therefore are ideally complemented by the high resolution images of MSI on Sentinel-2. The CTEP will provide access to OLCI L1 and L2 products, as well as L3 daily and weekly products at native resolution. For Sentinel-2, L1c and L2 images will be accessible over European coastal areas. Using extraction and format conversion tools, users will be able to obtain S2 and S3 BoA reflectances with compatible formats over the same area of interest in a given time frame. A major objective for the Coastal TEP is therefore to ease the connection between EO and in-situ data, thanks to a common data access portal and a set of automatic extraction and match-up tools. Finally, the coastal environment is a particularly sensitive to anthropogenic pressure, pollution and climate change. Long-term monitoring can be supported by the generation of homogeneous time series (multi-mission data alignment), but also by automatic trend detection tools. The CTEP will allow users to perform custom processing over a complete data archive without actually downloading the products. In addition, the CTEP will create a semantic database of features and events (localized in space and time), which can be used for example to record oil spills, flooding and storm surges and toxic algal blooms. The semantic database will be fed manually or by automatic feature detection on EO data, and will be a key tool for a multi-disciplinary approach. For instance, the semantic database will make it easy to look for optical data acquired over flooded areas identified from radar images. Finally, CTEP subscription services will allow users to perform automatic monitoring of some key indicators (water quality, water level, vegetation stress…) from Near Real Time data. In conclusion, the CTEP aims to provide new services and tools to enable a step change in the monitoring of coastal data, support a multi-disciplinary approach, and the provision of long term data series and innovative services.