New Method Maps Tides Far More Locally Using Coastline Satellite Images

Researchers from DTU Space in Denmark, working with the University of Oxford, the Technical University of Munich (TUM) and the German space technology company OHB, have developed a method to map tides far more locally using satellite images of coastlines, rather than relying only on scattered water-level gauges.

Tide height within a single bay can vary by up to one meter (3 feet) between two points just a few kilometers apart, but water-level gauges are typically spaced 50 kilometers (31 miles) or more apart, leaving large stretches of coastline, especially in sparsely populated areas, without direct measurements. The new method instead tracks the changing boundary between land and water across satellite images taken over more than 40 years by the U.S. Landsat program.

"With this method, we can instead use satellite images of the coastline to obtain a much more detailed picture of how tidal levels vary geographically along a given coastline," said Professor Ole Baltazar Andersen of DTU Space, a co-author of the study, which was published in the journal Communications Earth & Environment. By combining the coastline data with information about the beach's slope, researchers can calculate changes in water level and map tidal variations with far greater precision than previous methods.

"Variations in the coastline have often been regarded as noise that needed to be removed from satellite data. Here, we show that this noise can instead be used as a signal to map tidal patterns on a very local scale," said Michael Hart-Davis, a researcher at DGFI-TUM and the study's lead author. Andersen said the method could be particularly useful in places with few water-level gauges, such as Greenland, where he noted tidal variation differs greatly from Denmark's smaller, well-measured tides.