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K. Dörnhöfer, M. Liekefett, C. Fritz, N. Oppelt
Coastal and inland waters are threatened by multiple stressors such as climate change, eutrophication, contamination and degradation. Benthic macrophytes and water constituents are sensitive to environmental changes; they therefore represent key biological indicators for assessing the ecological state of water bodies within the European Water Framework Directive. Today, monitoring macrophytes and water constituents is still based on point based in situ mappings which cannot capture temporal and spatial dynamics. Satellite remote sensing, however, offers larger spatial coverage and higher temporal frequency for monitoring. Due to its improved radiometric and spectral resolution as well as signal-to-noise ratio the Landsat 8 OLI sensor is expected to be well-suited for remote sensing of water bodies. Bio-optical models relate the reflectance of a water body to concentrations of water constituents, benthos and water depths by means of radiative transfer. Within the project LAKESAT we tested the potential of Landsat 8 for mapping benthic macrophytes, bathymetry and water constituents at a test site in Mecklenburg-Western Pomerania, Northern Germany. We applied the bio-optical model WASI-2D to a scene acquired on 19th July 2014 at Lake Kummerow (53.808° N, 12.856° E). Concurrently taken water samples and submersible spectroradiometer measurements served to parameterise WASI-2D. Inverse modelling of the Landsat 8 reflectance spectra allowed deriving concentrations of chlorophyll a, suspended particulate matter and coloured dissolved organic matter in optically deep water; bathymetry and fractional coverage of bottom substrate via spectral endmembers, i.e. sandy sediment and dominant macrophytes (Potamogeton spp.) were retrieved in optically shallow parts of the lake. Chlorophyll a concentrations (<0.1 ±0.76 [micro]gl^-1) and absorption by coloured dissolved organic matter (0.71 ±0.13 m^-1) were low on average. Suspended particulate matter concentrations (7.21 ±1.68 mgl^-1) were slightly higher compared to analysed water samples. Benthos mappings showed predominating coverages of sandy sediment and single spots with dense macrophyte coverage which corresponds with visual observations. Landsat 8 derived bathymetry ranged between 0 and 1.6 m which matches with the official bathymetry chart. The results indicate that Landsat 8 is suitable for mapping water constituents, water depths and benthos and encourage to further take effort in using satellite data for lake monitoring.
Deutscher Luft- und Raumfahrtkongress 2015, Rostock
Deutsche Gesellschaft für Luft- und Raumfahrt - Lilienthal-Oberth e.V., Bonn, 2015
21,0 x 29,7 cm, 7 Seiten
Stichworte zum Inhalt:
bio-optical modelling, water quality