Background
Light substantially influences the biological, physical and chemical processes in the sea. The examples range from primary production over heat transfer to bleaching of CDOM (coloured dissolved organic matter, also denoted as Gelbstoff). Within the research focus Aquatic Optics, the scientists use spectroscopic methods in the range of ultraviolet and visible light for detecting substances and organisms in the water. Based on the substances' optical properties or with the help of special transducers even mixtures of substances can be quantified and categorised.

Tasks
The Aquatic Optics members develop, validate and optimise sensors, sensor systems and measuring platforms in order to detect dissolved and particulate matter in natural waters as well as in process water. Measurements are based on the inherent (independent of the natural light field) and apparent (dependent on the natural light field) optical properties of the substances. In addition, the researchers measure and model the spectral composition of the underwater light field and reflectance for remote sensing purposes. They also integrate sensors into networks and optimise their operation strategies.

Tools
Various hyperspectral radiometers measure radiance and irradiance both at fixed locations (stationary, e.g. reflectance for remote sensing applications) and covering entire areas in the water (profiling). In situ sensor systems and laboratory devices detect the photometric and fluorometric properties of substances within the spectral range of 200 to 1000 nm. The group uses both commercially available sensors and self-developed devices. There is a Horiba AquaLog for rapid EEM (Excitation-Emission-Matrix)-fluorometry with simultaneous absorption measurements. Depending on the intended use, different technologies are combined and equipped with additional sensors. In order to model the radiative transfer and optical interactions, the scientists use software such as Matlab and Hydrolight/ Ecolight.