Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun‐induced fluorescence in coastal waters

Abstract

[1] A model has been developed to retrieve phytoplankton absorption, a proxy for phytoplankton biomass, from observations of reflectance (R) and the diffuse attenuation coefficient (K d ) collected by moored radiometers in coastal waters, where high concentrations of chromophoric dissolved organic matter (CDOM) confound conventional ocean color algorithms. The inversion uses simultaneously two forward models: (1) a look-up table (LUT) that accounts for instrument geometry and the effect of the solar angle on both R and K d and (2) an analytical function describing the effects of Suninduced fluorescence (SIF) of chlorophyll on R. Estimates of phytoplankton biomass (mostly from SIF), the absorption by colored matter, and the particulate backscattering coefficients (mostly from the LUT) are obtained by optimizing the amplitude and shape of the absorption and backscattering coefficients in the forward model to best match the observations. An equation describing the quantum yield of fluorescence (photons fluoresced/photons absorbed) as a function of incident irradiance constrains the model and allows estimates of phytoplankton absorption. Innovations include: the utilization of both R and K d , providing good separation of the effects of backscattering from absorption; avoidance of reflectance bands between 400 and 600 nm, thereby avoiding interference from bottom reflection and CDOM fluorescence; utilization of the full emission band of SIF; and accounting for the irradiance-dependence of its quantum yield. The model effectively retrieved chlorophyll concentration from an independent data set -r = 0.76, n = 93, with a mean absolute percent error (MAPE) of 24%; this is better than a modern ocean color algorithm (OC4V4) on its validation data set, when restricted to the same range of chlorophyll (r = 0.67, n = 384, MAPE = 51%).Citation: Huot, Y., C. A. Brown, and J. J. Cullen (2007), Retrieval of phytoplankton biomass from simultaneous inversion of reflectance, the diffuse attenuation coefficient, and Sun-induced fluorescence in coastal waters,

Inferred influence of nutrient availability on the relationship between Sun‐induced chlorophyll fluorescence and incident irradiance in the Bering Sea

“…For Bering Sea waters of relatively high concentrations of CDOM and chlorophyll, we ignore Raman scatter [see Huot et al, 2007]:…”

Satellite-detected fluorescence reveals global physiology of ocean phytoplankton

“…Fluorescence emission under natural sunlight is also detectable in subsurface-and above-surface upwelling irradiance spectra (Neville and Gower, 1977;Morel and Prieur, 1977). Incident irradiance and pigment absorption strongly influence this "natural fluorescence" signal (e.g., Babin et al, 1996;Cullen et al, 1997;Ostrowska et al, 1997;Maritorena et al, 2000;Morrison, 2003;Westberry et al, 2003;Laney et al, 2005;Huot et al, 2007;Schallenberg et al, 2008), which was proposed originally as a tool for deriving phytoplankton photosynthetic rates (Topliss and Platt, 1986;Kiefer et al, 1989) and can register physiological variability (Letelier et al, 1997;Morrison, 2003). Such field observations were instrumental to the development of satellite fluorescence detection capabilities.…”

The measurement of phytoplankton biomass using flow‐cytometric sorting and elemental analysis of carbon

“…Recently, efforts have been made to relate light-scattering properties to C phyto , both in the field (Behrenfeld and Boss 2003;Behrenfeld and Boss 2006;Huot et al 2007;Westberry et al 2010) and from space (Behrenfeld et al 2005;Siegel et al 2005;Westberry et al 2008). Such assessments employ either measurements of particulate beam attenuation coefficients or particulate backscatter coefficients.…”