Abstract
Abstract. The coastline of the German Wadden Sea is constantly subjected to the tides and the tidal-induced environmental changes like erosion and accumulation of sediments need to be monitored constantly. This task requires digital elevation models (DEMs), which are derived from remote sensing data. To model those DEMs, a separation of data collected over landmasses and water bodies is required. In the GeoWAM project the potential of airborne SAR-data (F-SAR) is investigated for monitoring purposes in the Wadden Sea. As part of the project, this paper focuses on the suitability of F-SAR data regarding the derivation of water-land-boundaries (WLBs). Therefore, water-land-boundaries based on independent data sets are compared and evaluated. Analyzed data sets include data collected via F-SAR, airborne laserscanning (ALS), on site GNSS measured WLB points and sea-level data from two acoustic gauges. The algorithms were tested on a study site on Spiekeroog island. Our results show, that the accuracies of the derived WLBs mostly depend on the on-site topography and sediments. The spatial deviation between the reference data and the approximated WLBs is mostly less than 2 m horizontally and 0.15 m vertically. Identified challenges to overcome are mostly related to processing of F-SAR data in areas with highly water saturated sediments. Our results suggest, that F-SAR data in tidal flats is not necessarily dependent on further supplementing surveys, as one of the main advantages of the F-SAR data is the potential to derive DEMs and WLBs from the same data set.
Highlights
The German Wadden Sea is a highly dynamic environment, which is constantly subjected to the tides
By evaluating various methods to create reliable and accurate water-land boundaries, we demonstrated the potential of F-SAR to act as a new tool in topographical and environmental analysis in tidal areas
The F-SAR is especially suitable for remote study areas
Summary
The German Wadden Sea is a highly dynamic environment, which is constantly subjected to the tides. The necessity to monitor tidal-induced changes like erosion and accumulation of sediments and the associated changes of topography and coastlines rely on frequently updated high-resolution digital elevation models (DEMs). Important applications depending on those DEMs are e.g. marine navigation, environmental monitoring or coastal protection. Airborne laserscanning (ALS) is widely used for coastal DEM generation (Dorninger, 2011), but limitations of ALS (weather dependency, limited swath, flightline fusion) hamper further development in tidal areas (Bolz et al, 2020). Airborne SAR-data (F-SAR) is expected to overcome typical problems of ALS in tidal areas and aims to complement ALS data in the future (Horn et al, 2017). Improvements are expected due to a much higher swath and footprint at a comparable spatial resolution, complemented by high resolution multiband data sets (Pinheiro et al, 2020b)
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