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This thesis addresses methods for improving remote sensing of optically complex waters by: (1) establishing a laboratory environment (ENVILAB) for studying the dependence of spectral properties of phytoplankton on environmental conditions, (2) the development of a spectral model for the absorption and fluorescence properties of dissolved organic matter (GLEAM) as input to radiative transfer simulations, and (3), the advancing of remote sensing algorithms for water constituent retrieval under variable cloud cover. Die Arbeit befasst sich mit Methoden zur Verbesserung der Fernerkundung von optisch komplexen Gewässern durch: Erstens, die Realisierung einer Laborumgebung (ENVILAB) zur Untersuchung der Abhängigkeit spektraler Eigenschaften von Phytoplankton von Umweltbedingungen, Zweitens, die Entwicklung eines spektralen Modells der Absorption und Fluoreszenz gelöster organischer Stoffe (GLEAM) für Strahlungstransfer-Simulationen, und Drittens, die Weiterentwicklung von Fernerkundungsalgorithmen zur Ableitung von Wasserinhaltsstoffen bei variabler Bewölkung.

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.

The aquatic ecosystems of coastal and inland waters are more variable than the open ocean as water constituents and bottom substrates differ considerably in type, concentration and optical properties. Sensors with high spatial, spectral and radiometric resolution are therefore required to provide enough detail for mapping these highly complex environments. Two new hyperspectral Earth observation instruments, designed for monitoring spectrally complex areas, are the DLR Earth Sensing Imaging Spectrometer (DESIS) and the Environmental Mapping and Analysis Program (EnMAP). These hyperspectral sensors both cover a spectral range from 420 nm to 1000 nm in VNIR (and 900 nm -2450 nm in SWIR for EnMAP) and have a spatial resolution of 30 meters. DESIS was already launched to the ISS in summer 2018, EnMAP’s launch date will be in 2020. The goal of the present study is to specifically evaluate the performance of DESIS and EnMAP over aquatic ecosystems based on their sensor specifications. For this purpose, a sensitivity study was conducted in order to explore the spectral and radiometric properties of DESIS and EnMAP in the context of optically deep and shallow water mapping. The optical water properties and benthic cover types were chosen to represent typical inland and coastal waters. Forward simulations of hyperspectral measurements were made using the Water Color Simulator software WASI to study the expected DESIS and EnMAP radiances and their signal-to-noise ratios (SNR) for different atmospheric conditions. The impact of sensor noise on the retrieval of water constituents, benthos types and water depth was analyzed by applying inverse modelling to these reflectance spectra. The study assesses the mapping potential and limitations of a DESIS and EnMAP type sensor for these complex environments, which are usually much darker than land surfaces.

The aquatic ecosystems of coastal and inland waters are more variable than the open ocean as water constituents and bottom substrates differ considerably in type, concentration and optical properties. Sensors with high spatial, spectral and radiometric resolution are therefore required to provide enough detail for mapping these highly complex environments. A new Earth observation instrument, designed for monitoring spectrally complex areas, is the DLR Earth Sensing Imaging Spectrometer (DESIS). This hyperspectral sensor, which covers a spectral range from 450 nm to 950 nm and has a spatial resolution of 30 meters, will be launched to the ISS in summer 2018. The goal of the present study is to specifically evaluate the performance of DESIS over aquatic ecosystems based on its sensor specifications. For this purpose, a sensitivity study was conducted in order to explore the spectral and radiometric properties of DESIS in the context of optically deep and shallow water mapping. The optical water properties and benthic cover types were chosen to represent typical inland and coastal waters. Forward simulations of hyperspectral measurements were made using the Water Color Simulator software WASI to study the expected DESIS radiances and their signal-to-noise ratios (SNR) for different atmospheric conditions. The impact of sensor noise on the retrieval of water constituents, benthos types and water depth was analyzed by applying inverse modelling to these reflectance spectra. The study assesses the mapping potential and limitations of a DESIS type sensor for these complex environments, which are usually much darker than land surfaces.

Optic technologies and methods/procedures are established across all areas and scales in limnic and marine research in Germany and develop further continuously. The working group “Aquatic Optic Technologies” (AOT) constitutes a common platform for knowledge transfer among scientists and users, provides a synergistic environment for the national developer community and will enhance the international visibility of the German activities in this field. This document summarizes the AOT-procedures and -techniques applied by national research institutions. We expect to initiate a trend towards harmonization across institutes. This will facilitate the establishment of open standards, provide better access to documentation, and render technical assistance for systems integration. The document consists of the parts: Platforms and carrier systems outlines the main application areas and the used technologies. Focus parameters specifies the parameters measured by means of optical methods/techniques and indicates to which extent these parameters have a socio-political dimension. Methods presents the individual optical sensors and their underlying physical methods. Similarities denominates the common space of AOT-techniques and applications. National developments lists projects and developer groups in Germany designing optical hightechnologies for limnic and marine scientific purposes.

Meereswissenschaftliche Berichte No 97 2015 - Marine Science Reports No 97 2015, Optic technologies and methods/procedures are established across all areas and scales in limnic and marine research in Germany and develop further continuously. The working group “Aquatic Optic Technologies” (AOT) constitutes a common platform for knowledge transfer among scientists and users, provides a synergistic environment for the national developer community and will enhance the international visibility of the German activities in this field. This document summarizes the AOT-procedures and -techniques applied by national research institutions. We expect to initiate a trend towards harmonization across institutes. This will facilitate the establishment of open standards, provide better access to documentation, and render technical assistance for systems integration. The document consists of the parts: Platforms and carrier systems outlines the main application areas and the used technologies. Focus parameters specifies the parameters measured by means of optical methods/techniques and indicates to which extent these parameters have a socio-political dimension. Methods presents the individual optical sensors and their underlying physical methods. Similarities denominates the common space of AOT-techniques and applications. National developments lists projects and developer groups in Germany designing optical high-technologies for limnic and marine scientific purposes., Optische Technologien und Verfahren sind sowohl in der limnischen als auch marinen Forschung Deutschlands über alle Bereiche und Skalen etabliert und entwickeln sich rasant weiter. Die Arbeitsgruppe „Aquatische Optische Technologien“ (AOT) will Forschern und Anwendern eine Plattform bieten, die Wissenstransfer fördert, der nationalen Entwicklergemeinschaft ein synergistisches Umfeld eröffnet und die internationale Sichtbarkeit der deutschen Aktivitäten in diesem Forschungsfeld erhöht. Diese Zusammenfassung dokumentiert erstmalig die AOT-Verfahren und -Technologien, die von nationalen Forschungsinstitutionen eingesetzt werden. Wir erwarten, dass die Dokumentation einen Trend in Richtung institutsübergreifender Harmonisierung initiiert. Dies wird die Etablierung offener Standards, eine Verbesserung im Zugang zu Dokumentationen und gegenseitige technischer Hilfestellung bei (System-) Integrationen ermöglichen. Effizienz und Leistungsfähigkeit der AOT-Entwicklung und Anwendung auf nationaler Ebene werden von diesen Bestrebungen profitieren. Weitere Arbeitsgruppen und Entwickler werden ausdrücklich ermutigt, Kontakt aufzunehmen, um in einer späteren Auflage berücksichtigt zu werden. Das Dokument gliedert sich in mehrere Teile: Plattformen und Trägersysteme zeigt, wie optische Sensoren häufig eingesetzt werden, aus welchen Medien heraus und mit welcher Hintergrund-Technologie. Fokusparameter beschreibt die Größen, die mit Hilfe optischer Verfahren gemessen werden und zeigt, inwiefern diese Größen eine gesellschaftspolitische Dimension besitzen. Methoden stellt die einzelnen optischen Sensoren und die zu Grunde liegenden physikalischen Verfahren vor. Gemeinsamkeiten beschreibt die nationale Schnittmenge an AOT-Themen, -Verfahren und – Anwendungen. Nationale Entwicklungen listet eine Vielzahl von Projekten und Entwicklergruppen auf, die optische Hoch-Technologie für den limnischen und marinen Einsatz entwickeln. Aufgrund dieser Gliederung lassen sich im Text inhaltliche Wiederholungen nicht vermeiden, da z.B. bei der Darstellung der Parameter die verwendeten Methoden und deren Einsatz auf Geräteträgern angesprochen werden. Bei einer Aufzählung von Untersuchungsmethoden gilt dies entsprechend umgekehrt. Wir haben aus Gründen der Lesbarkeit und Eigenständigkeit der einzelnen Abschnitte diese Wiederholungen bewusst in Kauf genommen und ggf. Querverweise eingefügt.