Remote Sensing of the German North Sea Coast: A Review

Kurzfassung

The German North Sea coast is of immense economic, cultural, and environmental importance. It includes a portion of the Wadden Sea World Heritage Site, which extends into the Netherlands and Denmark and represents the largest system of tidal flats in the world. Monitoring of such important and sensitive habitats is critical for their informed management, and even more so in the face of a changing climate. Remote sensing (RS) provides an opportunity for consistent, low-cost monitoring, especially for difficult-to-access portions of the Wadden and North Sea. To date, however, no comprehensive review of RS applications for this area has been conducted, limiting its application for effective monitoring. This study summarizes RS efforts and findings in this region, as well as identifies gaps and opportunities. We conducted a literature review for the years 2000 to August 2024 that yielded 102 papers. We found that these papers ranged from measuring singular physical and biogeochemical metrics to habitat classifications and ecosystem integrity assessments. Papers could be grouped into four main research categories: coastal morphology (32%), water quality (31%), ecology (28%), and sediment (8%). Studies on intertidal topography were the most numerous, making up nearly 20% of papers. In the categories of water quality, ecology, and sediment, SST and chlorophyll, bivalves, and sediment transport were the main focuses, respectively. Over half of papers (64%) use satellite remote sensing, whereas about a third use airborne remote sensing. Multispectral data was by far the most commonly used data type in these studies, followed by SAR. Studies considered in this review span a wide range of spatial scales and resolutions, revealing that the two are generally correlated. Further, coastal morphology and ecology studies clearly cluster in high spatial resolution and small extents compared to water quality and sediment studies, which generally use lower spatial resolution but over larger study areas. Gaps identified in this review include coastal morphology and ecology studies at larger spatial scales, especially at scales that align with management areas such as the German Wadden Sea National Parks. Additionally, higher spatial resolution water quality studies, especially important in highly variable areas such as coastal zones, would help better characterize the highly dynamic nature of water quality in this area. Studies beyond this study area suggest that, with novel machine learning methods and advances in processing power, satellite RS has high potential to fill these gaps. This review finds that RS, and especially satellite-based RS, already plays a notable role in monitoring of the German North Sea coast and will likely continue to play a role in providing critical information for coastal managers.