Numerical simulation of light propagation in an integrating sphere containing a quartz layer between the cavity for water sample and fluorilon has been performed using Monte-Carlo method. It was shown that the use of the Lambertian model with a single parameter albedo is a good replacement for BRDF obtained by numerical simulation of light propagation in fluorilon. In addition, it was shown that for a given fluorilon configuration, there is an unambiguous relationship between the albedo and the transport scattering parameter, which depends on the scattering coefficient of fluorilon and the mean cosine of the phase function. This dependence is shown variations with a change in the fluorilon thickness and its absorption coefficient value.
The possibility of creating a bio-optical model for calculating parameters of underwater light fields under conditions of intense coccolithophore bloom in the Black Sea is shown. Hydrolight software is used for bio-optical modeling. The influence of the parameters of the bio-optical model both on the remote sensing reflectance spectrum and on the concentration of coccolithophores is demonstrated. The coccolithophore concentration is calculated using a regional algorithm. The optimal modeling parameters yield the remote sensing reflectance spectrum which nearly coincides with measured one. A decrease in the thickness of the coccolithophore layer relative to the optimal one leads to a comparable decrease in the concentration of coccolithophores, at the same time its increase does not play such a significant role. Estimates of the concentration of coccolithophores change little with variations in the concentration of chlorophyll, but they are more sensitive to changes in the amount of colored dissolved organic matter. The created bio-optical model made it possible to study the accuracy of chlorophyll estimation algorithms under conditions of intensive coccolithophore bloom.
Based on the data of shipborne measurements performed in the Atlantic sector of the Southern Ocean in January 2020, the Hydrolight hydrooptical model was configured to take into account the presence of the phycoerythrin pigment in phytoplankton cells. The use of this model will allow to validate and adjust the bio-optical algorithms for assessing the concentration of chlorophyll-a in the presence of phycoerythrin.
The results of the development and improvement of methods of field hydrooptical measurements are presented below, including the development of prototypes of a four-channel flow-through spectral fluorimeter and a deck spectroradiometer, as well as a complex for shipboard measurements of photosynthetically active radiation. The parameterization of the reflectance azimuthal dependence of an optically thick layer of sea ice and the numerical simulation of the formation of the light field structure in the integrating sphere using the Monte Carlo method are performed. The results of complex field studies obtained in Arctic expeditions of the Shirshov Institute of Oceanology, as well as in the northeastern part of the Black Sea, are presented. The results of modification and validation of regional satellite bio-optical algorithms are also shown. Using these algorithms, the data for the Atlas of bio-optical characteristics were updated and supplemented.
A method has been developed for calculating the spectral remote sensing reflectance based on the total upwelling radiance measurements, carried out from the ‘Optik’ Tu-134 aircraft laboratory over the Kara Sea on September 10, 2022. Data on the spectral downwelling irradiance and the reference remote sensing reflectance were obtained during synchronous underaircraft measurements from the R/V ‘Akademik Mstislav Keldysh’. To calculate the remote sensing reflectance, a simple two-parameter formula is proposed (with the relative error of 7%), the application of which allows one to separate the reflected from the surface radiation and take into account the variability of sky conditions due to the influence of variable cloudiness.
The study investigated vertical particle fluxes and associated environmental parameters in the southern part of the Kara Sea in September 2022 on the basis of a 5-day deployment of two moored Automatic Deep-Sea Sedimentation Observatories with sediment traps and CTD, currents and hydrooptical profilers.
This comparative study discusses the concentration and major phase composition of suspended particulate matter (SPM) derived from observations collected in the White, Barents and Kara seas in 2001–2021. A selective synthesis is based on our field data on SPM concentrations obtained from water samples and optical data determined from beam attenuation coefficient and light scattering revealed a pronounced difference of seawater optical properties of the western Arctic shelf of Eurasia. The heterogeneous origin of SPM in the studied Arctic seas largely determines different particle size distribution (PSD) and major phase composition of particulate matter in this region. This impacts the optical properties of the water column and hence primary production and sedimentation processes on the western Eurasian Arctic shelf. In recent decades, the dramatic changes in the Arctic climate system, including sea ice, affecting the concentration and composition of SPM as well as optical properties of sea water on the Barents Sea shelf becomes close to ice-free and seasonally ice-free shelves of the White and Kara seas. A pronounced benthic nepheloid layer (BNL) was reveled widespread in the studied seas but it has different thickness and SPM concentration. SPM distribution in the euphotic zone of the seas is much differs due to mostly various catchment-derived material, including river discharge (particulate and dissolved), and other natural geographical conditions. It is necessary to develop regional and seasonal algorithms linking in situ data with remote sensing of bio-optical characteristics of sea water of the Eurasian Arctic shelf.
Analysis of bio-optical and hydrochemical characteristics was performed on samples taken along the route of the vessel in five seas: the Baltic, North, Norwegian, Barents and White. It has been shown that the values of the absorption coefficient of colored dissolved organic matter, as well as the concentrations of silicates, can be used to assess the developmental stages of phytoplankton. Simultaneous measurements of fluorescence and colored dissolved organic matter absorption coefficient made it possible to see a clear separation of the optical properties of the studied seas.
During the scientific expedition "European Arctic - 2020" on the R/V "Akademik Mstislav Keldysh" (cruise No. 80), the concentration of chlorophyll a, spectral coefficients of light absorption by phytoplankton pigments, non-algal particles and colored dissolved organic matter have been measured in the euphotic layer of the Norwegian and the Barents Seas, and in the Arctic Ocean from July 28 to August 23, 2020. High variability of bio-optical properties, heterogeneity of the studied water area in terms of the relative contribution of colored dissolved organic matter to the total lightu absorption was revealed. Relationship between the total light absorption at 438 and 490 nm in the surface layer and the photosynthesis zone has been obtained.
The work is devoted to the study of the effect of phycoerythrin pigment on the seawater optical properties in the Atlantic sector of the Southern Ocean. The investigation was carried out in the 79th expedition of the R / V “Akademik Mstislav Keldysh” in January 2020. At some stations, a high content of phycoerythrin was registered in the fluorescence spectra of seawater, the light absorption spectra by suspended particles, and in the remote sensed reflectance spectra of seawater. In particular, the fluorescence of this pigment induced by solar radiation was recorded in ocean color data. The presence of phycoerythrin can lead to uncertainties of the chlorophyll-a concentration estimates from satellite data retrieved with standard algorithms.
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