Supporting maritime forecast with Sentinel-1 satellite Near Real Time services: observations of wind, sea state and coastal processes

Kurzfassung

Innovative algorithms for Sentinel-1 (S1) satellite allow daily observations of meteo-marine parameters, tracking of storm propagation, study of local sea state variability and coastal processes. In order to investigate geophysical processes, the sea state and wind fields estimated simultaneously from S1 scenes acquired twice daily are combined with numerical forecast model results and in-situ measurements. The focus of the investigations are the evolution and propagation of storm peaks/centres, storm front movement, and arrival of swell. An example of efficient storm tracking in the Black Sea in April 2017 over three days is analysed. The HZG forecast spectral wave model running for the Black Sea reproduces the storm peak propagation near to the S1 observations. In detail, the storm peak observed by S1 is shifted ~80km towards the south in comparison to the model simulations. During this storm, the ship “Geroi Arsenala” of river-sea class licensed for inland waterways with access to the coastal seas was capsized about 40 kilometres to the south of the Kerch Strait in the open Black Sea, according to the associated press. The cargo ship was carrying grain from Russia to Turkey. Obviously, the course was taken too far from the coast to shorten the way across the sea with unexpected high sea state. Only one of the 12 people aboard was rescued. This is a tragic incident that proves the importance of Maritime Safety and Security. With the Sentinel satellites and the processing framework demonstrated in this work, we have appropriate tools to raise Maritime Situation Awareness (MSA) to unprecedented levels, which helps avoiding such accidents. The rapid development of satellite techniques, information extraction algorithms and ground infrastructures during the last years enabled a series of oceanographic applications with near-real-time (NRT) capabilities. Several minutes after acquisition, the produced data with geo-coded information on wind speed and wave height can be transferred to the weather services for validation of the forecasting models. The different kind of data like coastline, wave height, surface wind speed, ice coverage, oil spills etc. can be processed in parallel for the same image and combined with other information (e.g. model results, ship traffic) for supporting MSA. The algorithms currently developed for this purpose are integrated into a prototype processor for Sentinel-1 imagery. The DLR Ground Station Neustrelitz applies this prototype as part of a near real-time demonstrator MSA service. The presented scientific service involves daily provision of surface wind and sea state parameters estimated fully automatically from S1 Wide Swath Mode (IW) Synthetic Aperture Radar (SAR) images of North and Baltic Sea. S1 IW covers area-strips of thousand kilometres of earth and ocean surface with a resolution of ~10m by sequences of multiple individual IW images with an approximate size of 200km×250km. The data are free to use and provide unprecedented observation possibilities of ocean processes and natural phenomena worldwide at a high repetition rate. Due to the independence of sunlight and cloud coverage, SAR data are an indispensable source of 2D information of the ocean surface for open sea and for coastal applications.