Global coastal attenuation of wind-waves observed with radar altimetry
Knowledge of ocean wave heights at the coast is essential for several operational applications, ranging from coastal protection to energy exploitation. In this context, the Significant Wave Height (SWH) is one of the most general quantitative parameters that describe the sea state at a particular location. SWH, representing the average height of the highest waves, can be measured from satellites using radar altimeters. Over the open ocean, such measurements are routinely used, for example, for ocean weather predictions. In the coastal zone however, the radar measurements were not considered reliable. As an alternative, in-situ buoys or high-resolution ocean models are employed. While the network of in-situ buoys is very sparse and can only provide data at specific locations, appropriate ocean models are computationally very expensive and not globally available, besides requiring constant validation.
Led by DGFI-TUM, an international team has now analyzed reprocessed data from radar altimetry, specifically tailored to improve the quality and quantity of coastal measurements. The results, published in the article Global coastal attenuation of wind-waves observed with radar altimetry (Nature Communications, 2021, doi: 10.1038/s41467-021-23982-4, [PDF]), provide a global picture of the average wave climate when going from offshore (about 30 km) to the coast (up to 3 km from land). The typical attenuation of the waves when approaching the coast, for example due to the shading effect from the land, is quantified to be about 20% of the wave height reached offshore. As a consequence, the energy flux transported by the waves is calculated to decline by about 40% on a global average. This result is paramount for coastal assessments, which until now are often based on models with validation relative to offshore satellite altimetry data.
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