Publications
Following publications have been announced by our department Optical Oceanography. For further information please contact the marked authors of the publications:
Bi, S., & Hieronymi, M. (2024): Holistic optical water type classification for ocean, coastal, and inland waters. Limnol Oceanogr., doi:10.1002/lno.12606
Abstract:
Water constituents exhibit diverse optical properties across ocean, coastal, and inland waters, which alter their remote-sensing reflectance obtained via satellites. Optical water type (OWT) classifications utilized in satellite data processing aim to mitigate optical complexity by identifying fitting ocean color algorithms tailored to each water type. This facilitates comprehension of biogeochemical cycles ranging from local to global scales. Previous OWT frameworks have focused narrowly on either oceanic or inland waters and have relied too heavily on specific data collections. We propose a novel holistic OWT framework applicable to all natural waters, based on state-of-the-art bio-geo-optical modeling and radiative transfer simulations that encompass different phytoplankton groups. This framework employs a “knowledge-driven” paradigm, combining domain knowledge and insights from previous studies to simulate the reflectance spectrum from water constituent concentrations and inherent optical properties. Our method extracts optical variables to represent the full spectrum of reflectance, consolidating both spectral shape and magnitude. We apply the framework utilizing diverse in situ, synthetic, and satellite data (Sentinel-3 OLCI) and demonstrate its better classifiability than other frameworks. This framework lays the foundation for comprehensive global monitoring of natural waters.
Novak, M.G., Burmeister, H., & Röttgers, R. (2024): Hyperspectral measurements of light backscattering by particles in water with a fixed angle setup: proof of concept and instrument calibration. Opt. Express, Vol. 32, Issue 13, pp. 23722-23735, doi:10.1364/OE.529061
Abstract:
The light backscatter signal is the fraction of light scattered at angles greater than 90 degrees with respect to the direction of the incident light. Optical remote sensing platforms collect this signal, which, when measured from the ocean, holds crucial information about its constituents. Interpretation of this signal demands a rigorous understanding of scattering by water and by particles in water. Previous backscatter measurements have mainly focused on resolving the angular distribution of scattering with much less attention given to resolving the wavelength component of backscatter. Most heritage sensors have looked at most 9 wavelengths of light at one scattering angle. Just recently an in situ sensor was presented that can measure backscattering with a 10 nm resolution. Here, we present a laboratory hyperspectral backscatter setup capable of measuring from the ultraviolet to near-infrared wavelengths (320 – 850 nm) at 2 nm resolution.
Lomas, M.W., Neeley, A. R., Vandermeulen, R., Mannino, A., Thomas, C., Novak, M.G., & Freeman, S.A. (2024): Phytoplankton optical fingerprint libraries for development of phytoplankton ocean color satellite products. Scientific Data, 11(1), 168, doi:10.1038/s41597-024-03001-z
Abstract:
Phytoplankton respond to physical and hydrographic forcing on time and space scales up to and including those relevant to climate change. Quantifying changes in phytoplankton communities over these scales is essential for predicting ocean food resources, occurrences of harmful algal blooms, and carbon and other elemental cycles, among other predictions. However, one of the best tools for quantifying phytoplankton communities across relevant time and space scales, ocean color sensors, is constrained by its own spectral capabilities and availability of adequately vetted and relevant optical models. To address this later shortcoming, greater than fifty strains of phytoplankton, from a range of taxonomic lineages, geographic locations, and time in culture, alone and in mixtures, were grown to exponential and/or stationary phase for determination of hyperspectral UV-VIS absorption coefficients, multi-angle and multi-spectral backscatter coefficients, volume scattering functions, particle size distributions, pigment content, and fluorescence. The aim of this publication is to share these measurements to expedite their utilization in the development of new optical models for the next generation of ocean color satellites.
Röttgers, R., Novak, M.G., & Belz, M. (2024): Measurement of light absorption by chromophoric dissolved organic matter using a type-II liquid capillary waveguide: assessment of an achievable accuracy. Applied Optics, Vol. 63, Issue 14, pp. 3811-3824, doi:10.1364/AO.516580
Abstract:
Light absorption by chromophoric dissolved organic matter (CDOM) in the ocean is often measured using liquid waveguide capillary cells coupled to spectral array detectors. This type of optical setup is affected by several sources of uncertainties related to the waveguide and the detector. Uncertainties from the waveguide arise from errors in the effective path length and the effects of water salinity, while errors related to the detector are due to the non-linearity in the response, internal stray light, and wavelength accuracy. Here, uncertainties in the measurements of the spectral absorption coefficient of CDOM due to the optical setup itself were investigated in detail. The related systematic errors were very often significant (2–15%) and larger than expected from simple measurement uncertainty (${\pm}{1}\%$). However, they can be corrected by characterizing the detector’s response for non-linearity and stray light, regularly performing calibrations for the detector’s wavelength response, and routinely measuring the waveguide’s effective path length. Including such corrections and timely calibrations reduces the uncertainties related to the spectrophotometric measurements to about ${\pm}{2}\%$. Uncertainties related to the necessary handling of samples are not included here.
