Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

A New Retrieval of Sun-Induced Chlorophyll Fluorescence in Water from Ocean Colour Measurements Applied on OLCI L-1b and L-2

Version 1 : Received: 22 September 2020 / Approved: 23 September 2020 / Online: 23 September 2020 (16:39:53 CEST)

How to cite: Kritten, L.; Preusker, R.; Fischer, J. A New Retrieval of Sun-Induced Chlorophyll Fluorescence in Water from Ocean Colour Measurements Applied on OLCI L-1b and L-2. Preprints 2020, 2020090554 (doi: 10.20944/preprints202009.0554.v1). Kritten, L.; Preusker, R.; Fischer, J. A New Retrieval of Sun-Induced Chlorophyll Fluorescence in Water from Ocean Colour Measurements Applied on OLCI L-1b and L-2. Preprints 2020, 2020090554 (doi: 10.20944/preprints202009.0554.v1).

Abstract

The retrieval of sun-induced chlorophyll fluorescence is greatly beneficial to studies of marine phytoplankton biomass, physiology, and composition and is required for user applications and services. Customarily phytoplankton chlorophyll fluorescence is determined from satellite measurements through a fluorescence line-height algorithm using three bands around 680 nm. We propose here a modified retrieval, making use of all available bands in the relevant wavelength range with the goal to improve the effectiveness of the algorithm in optically complex waters. For the Ocean and Land Colour Instrument (OLCI) we quantify a Fluorescence Peak Height from fitting a Gaussian function and related terms into the top-of-atmosphere reflectance bands between 650 and 750 nm. This algorithm retrieves, what we call Fluorescence Peak Height from fitting a Gaussian function upon other terms to top-of-atmosphere reflectance bands between 650 and 750 nm. This approach is applicable to Level-1 and Level-2 data. We find a good correlation of the retrieved fluorescence product to global in-situ chlorophyll measurements, as well as a consistent relation between chlorophyll concentration and fluorescence from radiative transfer modelling and OLCI/in-situ comparison. The algorithm is applicable to complex waters without needing an atmospheric correction and vicarious calibration and features an inherent correction of small spectral shifts, as required for OLCI measurements.

Subject Areas

Remote Sensing; Ocean Colour; Retrievals; Fluorescence; Optical Properties; Satellite; Spectral; Radiative Transfer; optically complex waters; chlorophyll; absorption; scattering

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