Oral Session 2

Significance of spectral scattering of microalgae and cyanobacteria in forward and inverse model for hyperspectral monitoring of massive blooms

Optical sensing of the aquatic environment relies on the radiation exiting the water body measurable by radiometers above the water surface or aboard satellites. Light propagation within the water column is controlled by the balance between absorption and scattering eventually leading to the water-leaving radiance. It is common-practice to approximate the radiative transfer equation by non-linear equations relating the water-leaving radiance (or the remote sensing reflectance) to a ratio of the bulk absorption and backscattering coefficients. In the case of massive blooms, the absorbing pigments of the microalgae or cyanobacteria greatly alter the water-leaving radiance with conspicuous discoloration visible from space. Over decades, numerous efforts have been made to collate and document the species-specific absorption properties of the phytoplankton in relation to their absorbing pigment concentration. In contrast, far less data have been collected and analyzed concerning the phytoplankton scattering properties. In this study, the importance of the scattering properties is investigated in the case of massive coastal or inland blooms. The analysis is based on the volume scattering function (from LISST-VSF) and hyperspectral backscattering (from HiFi-bb) coefficient obtained for several species from a laboratory experiment. The absorption impact on scattering (anomalous dispersion) is first investigated. Then, the data set is used within radiative transfer and its backscattering-absorption ratio approximation to study the impact of species-specific scattering and potential identification of dominant species. Case studies and validation are discussed based on applications to in situ and PRISMA satellite hyperspectral data.

Tristan Harmel, Magellium, France, https://orcid.org/0000-0002-1172-9636

Rüdiger Röttgers, HEREON, Germany

Chintan Maniyar, Remote Sensing and Spectroscopy Lab, University of Georgia, USA

Daria Malik, Magellium, France

Guillaume Morin, Magellium, France

Nima Pahlevan, Science Systems and Applications Inc. (SSAI) and NASA Goddard Space Flight Center, USA

Antonio Ruiz-Verdù, Image Processing Laboratory (IPL), University of Valencia, Spain

Laura Zoffoli, Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine (CNR ISMAR), Italy

Pierre Gernez, Nantes Université, Institut des Substances et Organismes de la Mer, France

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