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Remote Sens. 2018, 10(2), 181; doi:10.3390/rs10020181

Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany)

1
Department of Civil, Geo and Environmental Engineering, Remote Sensing Technology, Technical University of Munich (TUM), Arcisstr. 21, D-80333 München, Germany
2
German Aerospace Center, Remote Sensing Technology Institute, Münchner Str. 20, Oberpfaffenhofen, D-82234Weßling, Germany
3
Department of Experimental Limnology, Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Alte Fischerhütte 2, D-16775 Stechlin, Germany
4
Institute of Biochemistry and Biology, Potsdam University, Maulbeerallee 2, D-14476 Potsdam, Germany
5
Earth Observation and Modelling, Department of Geography, Kiel University, Ludewig-Meyn-Str. 14, D-24098 Kiel, Germany
6
Helmholtz-Zentrum Geesthacht, Center for Materials and Coastal Research, Institute for Coastal Research, Max Planck Str. 1, D-21502 Geesthacht, Germany
*
Author to whom correspondence should be addressed.
Received: 6 November 2017 / Revised: 17 January 2018 / Accepted: 19 January 2018 / Published: 26 January 2018
(This article belongs to the Special Issue Remote Sensing of Water Quality)
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Abstract

Remote sensing and field spectroscopy of natural waters is typically performed under clear skies, low wind speeds and low solar zenith angles. Such measurements can also be made, in principle, under clouds and mixed skies using airborne or in-situ measurements; however, variable illumination conditions pose a challenge to data analysis. In the present case study, we evaluated the inversion of hyperspectral in-situ measurements for water constituent retrieval acquired under variable cloud cover. First, we studied the retrieval of Chlorophyll-a (Chl-a) concentration and colored dissolved organic matter (CDOM) absorption from in-water irradiance measurements. Then, we evaluated the errors in the retrievals of the concentration of total suspended matter (TSM), Chl-a and the absorption coefficient of CDOM from above-water reflectance measurements due to highly variable reflections at the water surface. In order to approximate cloud reflections, we extended a recent three-component surface reflectance model for cloudless atmospheres by a constant offset and compared different surface reflectance correction procedures. Our findings suggest that in-water irradiance measurements may be used for the analysis of absorbing compounds even under highly variable weather conditions. The extended surface reflectance model proved to contribute to the analysis of above-water reflectance measurements with respect to Chl-a and TSM. Results indicate the potential of this approach for all-weather monitoring. View Full-Text
Keywords: remote sensing; inland water; hyperspectral measurements; in-situ; cloud; surface reflection; inversion; bio-optical modeling remote sensing; inland water; hyperspectral measurements; in-situ; cloud; surface reflection; inversion; bio-optical modeling
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Göritz, A.; Berger, S.A.; Gege, P.; Grossart, H.-P.; Nejstgaard, J.C.; Riedel, S.; Röttgers, R.; Utschig, C. Retrieval of Water Constituents from Hyperspectral In-Situ Measurements under Variable Cloud Cover—A Case Study at Lake Stechlin (Germany). Remote Sens. 2018, 10, 181.

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