Analysis of the Variability of the Optical Properties of Water in the Black Sea in Summer 1998 According to the Data of a SeaWiFS Satellite Instrument

We study examples of surveys of the Black Sea performed with the help of a SeaWiFS satellite instrument. It is shown that the results of measurements carried out in spectral channels of 510 and 555nm give information on the basic specific features of the space and time variability of the characteristics of absorption and scattering of light in seawater. The use of a spectral channel of 412nm is inefficient due to the low reliability of the results of the procedure of atmospheric correction performed according to standard algorithms. The results of model calculations demonstrate that the predominant contribution to the absorption of light in the Black Sea in summer is made by the yellow substance.     

Intensification of light scattering as a result of mixing of pure waters with different densities

In experiments aimed at measuring the spectral volume scattering function of light, we obtain an additional confirmation of the existence of two-dimensional inhomogeneities of water on scales of 10^-7–10^-3 m. In the case of mixing of pure water with small amounts of filtered water with different temperature or salinity, we observe an 1.8–4.5-fold intensification of the scattering of light in the entire range of angles. It is shown that this effect can be explained neither by turbulence nor by the formation of dissipative structures. We estimate the sizes of inhomogeneities affecting the spectral volume scattering function of light.     

A spectral model of underwater irradiance in the Black Sea

We develop a semiempirical spectral model of penetrating irradiance taking into account the biooptical characteristics of the Black Sea. The evaluation of the contributions of the principal optically active components to the total absorption of light in the sea shows that, in the short-wave range (400–500 nm), light is mainly absorbed by the dissolved organic matter (41–77%). The contribution of phytoplankton to the total absorption attains its maximum values (26–37%) in the abyssal part of the sea in the period of spring blooming of diatoms. In the coastal waters, the absorption of light by suspended nonalgae particles in summer is almost twice as intense (20–30%) as in the open sea (8–13%). The analysis of the sensitivity of our model shows that the absorption of light by dissolved organic matter is more significant for the estimation of the photosynthetically active radiation in the Black Sea than the concentration of pigments and backscattering of light by suspended particles. The comparison of the results of model computations with the data of measurements of the underwater irradiance reveals high accuracy of the proposed model.     

应用CDOM光学特性估算水体COD——以辽宁省盘锦市双台子河和辽东湾为例

有色可溶性有机物(chromophoric dissolved organic matter,CDOM)是水体中一类重要的光吸收物质,在水色遥感中,其光学特性主要以440 nm处的吸收系数和光谱斜率来表征,利用这些光学特性进行水环境要素遥感反演具有较广泛的应用前景.化学需氧量(chemical oxygen deman...     

Bio-Optical Properties of Seawater in the Western Subarctic Gyre and Alaskan Gyre in the Subarctic North Pacific and the Southern Bering Sea during the Summer of 1997

Chlorophyll a concentrations (chla) and the absorption coefficients of total particulate matter [a _p()], phytoplankton [a _ph()], detritus [a _d()], and colored dissolved organic matter: CDOM [a _CDOM()] were measured in seawater samples collected in the subarctic North Pacific and the southern Bering Sea during the summer of 1997. We examined the specific spectral properties of absorption for each material, and compared the light fields in the Western subarctic Gyre (area WSG) with those in the Alaskan Gyre (area AG), and the southern Bering Sea (area SB). In the area WSG, the irradiance in the surface layer decreased markedly, indicating high absorption. In the area AG, the radiant energy penetrated deeply, and the chl a and absorption values were low throughout the water column. In the area SB, light absorption was high in the surface layer on the shelf edge and decreased with increasing depth; on the other hand, light absorption was low in the surface layer in the shelf area and increased with increasing depth.     

Analysis of ocean color spectra (I)

By using the two-flow optical model, the variation in the irradiance reflectance of the ocean just below the surface has been calculated for varying water optical properties, for the interpretation of remotely-sensed ocean color data. The input variables used in our model are the concentration of phytoplankton (chlorophyll-a), the absorption coeffiicient of yellow substance, the particle scattering coefficient, the ratio of the back-scattering coefficient to the total scattering coefficient of particles, and the ratio of the absorption to scattering coefficients for particles.The irradiance reflectance increases monotonically with the ratio of the back-scattering coefficient to the total scattering coefficient. Spectral changes occur in the irradiance reflectance for increases in chlorophyll-a concentration and yellow substance as well as the ratio of the absorption to scattering coefficients.Because slightly different mathematical expressions have been derived by other investigators using the two-flow model, an evaluation of the resulting calculation differences is presented and discussed.     

Effect of finely divided admixtures on the scattering of light in “pure” filtered water

We consider the problem of disagreement between the theoretical and experimental values of the spectral volume scattering function of “pure” filtered water. To explain this disagreement, we advance a hypothesis of existence of two-dimensional space correlations between the locations of a finely divided suspension in the liquid. We deduce analytic relations for the scattering of light in the approximation of statistically equilibrium distribution of particles over the surfaces of spheres randomly arranged in the medium. The experimental data on the volume scattering function of “pure” filtered water (the sizes of particles do not exceed 0.2 μm) are analyzed. The results of numerical analysis according to the model of spherical surface distribution of finely divided particles in water are in qualitative agreement with the spectral volume scattering function of filtered water. __________ Translated from Morskoi Gidrofizicheskii Zhurnal, No. 2, pp. 46–56, March–April, 2008.     

用于海洋-大气辐射传递计算的光学参数数据库

开发和建立了用于海洋-大气辐射传递计算的光学参数数据库.它包括海中主要成分(纯海水、浮游植物、悬移质、可溶有机物)的固有光学参数(光谱吸收系数、光谱散射系数等)及大气中主要气溶胶的有关光学参数.在这些光学参数中,大多数是来自现场的直接测量,一些是间接测量获取,还有一些是通过理论计算得到.     

Indicatrices of Scattering of Light and the Composition of Suspension in the Black Sea

We analyze the data of measurements of the indicatrices of scattering of light in the Black Sea in winter 1991 and summer 1998, present their principal characteristics, and discuss their correlations and spatial variability. The data on scattering of light are used to determine the number and weight concentrations of various fractions of particles suspended in water. The characteristics of scattering of light and the composition of suspension in the Black Sea are compared with the data obtained in 1973 and with the data accumulated in the Aegean and Ionian Seas and in the Indian Ocean.__________Translated from Morskoi Gidrofizicheskii Zhurnal, No. 1, pp. 63–76, January–February, 2005.     

Brown Carbon and Black Carbon in the Smoky Atmosphere during Boreal Forest Fires

We have investigated the variability of smoke aerosol absorbing ability with variations in the content of brown carbon (BrC) and black carbon (BC). Using monitoring data on radiative characteristics of smoke aerosol at AERONET stations and the spatial distribution of aerosol optical depth (AOD) obtained by the MODIS spectrometer (Terra satellite), we have detected large-scale smokes during boreal forest fires in Russia and Canada (1995–2012). The spatial distribution (50°–70° N, 95°–125° W) and temporal variability (at AERONET station Fort McMurray) of AOD during the smoking of a part of Canada in July 2012 have been analyzed. AOD probability distributions for July 14–18, 2012, and an estimate of aerosol radiative forcing of smoke aerosol at the upper boundary of the atmosphere have been obtained. We have proposed a technique for the diagnostics of BrC and BC in smoke aerosol particles from the spectral dependence of the imaginary part of the refractive index. At a wavelength of 440 nm, the contributions of BrC and BC to the smokeaerosol absorbing abitity can be comparable in magnitude. In many cases, the absorption spectra of smoke aerosol can be adequately approximated by either power or exponential functions. The presence of BrC in smoke-aerosol particles highly extends the variety of observed absorption spectra in a smoky atmosphere and spectral dependences of single scattering albedo. In the spectral range of 440–1020 nm, the radiative characteristics of smoke aerosol are largely contributed by its fine mode.     

Modeling ocean primary production: Sensitivity to spectral resolution of attenuation and absorption of light

Modeling the vertical penetration of photosynthetically active radiation (PAR) through the ocean, and its utilization by phytoplankton, is fundamental to simulating marine primary production. The variation of attenuation and absorption of light with wavelength suggests that photosynthesis should be modeled at high spectral resolution, but this is computationally expensive. To model primary production in global 3d models, a balance between computer time and accuracy is necessary. We investigate the effects of varying the spectral resolution of the underwater light field and the photosynthetic efficiency of phytoplankton (α^*), on primary production using a 1d coupled ecosystem ocean turbulence model. The model is applied at three sites in the Atlantic Ocean (CIS (60°N), PAP (50°N) and ESTOC (30°N)) to include the effect of different meteorological forcing and parameter sets. We also investigate three different methods for modeling α^* – as a fixed constant, varying with both wavelength and chlorophyll concentration [Bricaud, A., Morel, A., Babin, M., Allali, K., Claustre, H., 1998. Variations of light absorption by suspended particles with chlorophyll a concentration in oceanic (case 1) waters. Analysis and implications for bio-optical models. J. Geophys. Res. 103, 31033–31044], and using a non-spectral parameterization [Anderson, T.R., 1993. A spectrally averaged model of light penetration and photosynthesis. Limnol. Oceanogr. 38, 1403–1419]. After selecting the appropriate ecosystem parameters for each of the three sites we vary the spectral resolution of light and α^* from 1 to 61 wavebands and study the results in conjunction with the three different α^*estimation methods. The results show modeled estimates of ocean primary productivity are highly sensitive to the degree of spectral resolution and α^*. For accurate simulations of primary production and chlorophyll distribution we recommend a spectral resolution of at least six wavebands if α^* is a function of wavelength and chlorophyll, and three wavebands if α^* is a fixed value.     

Bio-Optical Relationship of Case I Waters: The Difference between the Low- and Mid-Latitude Waters and the Southern Ocean

Both historic and currently operational chlorophyll algorithms of the satellite-borne ocean color sensors, such as SeaWiFS, were evaluated for in situ spectral radiation and chlorophyll data in some Case I waters, including the waters in the Indian Ocean sector of the Southern Ocean. Chlorophyll a concentration of the data set (n = 73) ranged from 0.04 to 1.01 mg m^–3. The algorithms had higher accuracy for the low- and mid-latitude waters (RMSE: 0.163–0.253), specifically the most recently developed algorithms of OCTS and Sea WiFS showed 0.163 and 0.170 of Root Mean Square Errors, respectively. However, these algorithms had large errors (0.422–0.621) for the Southern Ocean data set and underestimated the surface chlorophyll by more than a factor of 2.6. The absorption coefficients in the blue spectral region retrieved from remote sensing reflectance varied in a nonlinear manner with chlorophyll a concentration, and the value in the Southern Ocean was significantly lower than that in the low- and mid-latitude waters for each chlorophyll a concentration. The underestimation of chlorophyll a concentration in the Southern Ocean with these algorithms was caused by the lower specific absorption coefficient in the region compared with the low- and mid-latitude waters under the same chlorophyll a concentration.     

Photobleaching of chromophoric dissolved organic matter in natural waters: kinetics and modeling

The effects of monochromatic and polychromatic UV and visible (VIS) radiation on the optical properties (absorption and fluorescence) of chromophoric dissolved organic matter (CDOM) were examined for a Suwannee River fulvic acid (SRFA) standard and for water from the Delaware and Chesapeake Bays. The primary (direct) loss of absorption and fluorescence occurred at the irradiation wavelength(s), with smaller secondary (indirect) losses occurring outside the irradiation wavelength(s). The efficiency of both direct and indirect photobleaching decreased monotonically with increasing wavelength. Exposure to polychromatic light increased the CDOM absorption spectral slope (S), consistent with previous field measurements. An analysis of the monochromatic photobleaching kinetics argues that a model based on a simple superposition of multiple chromophores undergoing independent photobleaching cannot apply; this conclusion further implies that the absorption spectrum of CDOM cannot arise solely from a simple superposition of the spectra of numerous independent chromophores. The kinetics of CDOM absorption loss with the monochromatic irradiation were employed to create a simple, heuristic model of photobleaching. This model allowed us to examine the importance of the indirect photobleaching losses in determining the overall photobleaching rates as well as to model the photobleaching of natural waters under polychromatic light fields. Application of this model to natural waters closely predicted the change in the CDOM spectral shape caused by photodegradation. The time scale of this process was consistent with field observations acquired during the summertime for coastal waters in the Middle Atlantic Bight (MAB). The results indicate that the ratio of the photodegradation depth to the mixed layer depth is a key parameter controlling the rate of the photobleaching in surface waters.     

Characterization of the solar light field within the ocean mesopelagic zone based on radiative transfer simulations

The solar light field within the ocean from the sea surface to the bottom of the mesopelagic zone was simulated with a radiative transfer model that accounts for the presence of inelastic radiative processes associated with Raman scattering by water molecules, fluorescence of colored dissolved organic matter (CDOM), and fluorescence of chlorophyll-a contained in phytoplankton. The simulation results provide a comprehensive characterization of the ambient light field and apparent optical properties (AOPs) across the entire visible spectral range within the depth range 200–1000 m of the entire mesopelagic zone for varying chlorophyll-a concentration and seawater optical properties in the mixed surface layer of the ocean. With increasing depth in the mesopelagic zone, the solar irradiance is reduced by ~9–10 orders of magnitude and exhibits a major spectral maximum in the blue, typically centered around a light wavelength of 475 nm. In the green and red spectral regions, the light levels are significantly lower but still important owing to local generation of photons via inelastic processes, mostly Raman scattering and to a lesser extent CDOM fluorescence. The Raman scattering produces a distinct secondary maximum in irradiance spectra centered around 565 nm. Comparisons of our results with light produced by the radioactive decay of the unstable potassium isotope contained in sea salt (⁴⁰K) indicates that the solar irradiance dominates over the ⁴⁰K-produced irradiance within the majority of the mesopelagic zone for most scenarios considered in our simulations. The angular distribution of radiance indicates the dominance of downward propagation of light in the blue and approach to uniform distribution in the red throughout the mesopelagic zone. Below the approximate depth range 400–500 m, the shape of the angular distribution is nearly invariant with increasing depth in the green and red and varies weakly in the blue. The AOPs at any light wavelength also assume nearly constant values within the deeper portion of the mesopelagic zone. These results indicate that the mesopelagic light field reaches a nearly-asymptotic regime at depths exceeding ~400–500 m.     

Empirical analysis of the aerosol effect on the spectral brightness variability in the ocean-atmosphere system

A statistical analysis of the variations of the brightness coefficient in the ocean-atmosphere system in the visible band was carried out using the results of remote measurements from the INTERKOSMOS-21 satellite. The variability of the seawater optical parameters and the Rayleigh component of light scattering were eliminated by computing the variations of the signals from the local average values along the route of measurements. The derived spectral dependence of the aerosol scattering component is characterized by a slight increase when the wavelength increases.Translated by Mikhail M. Trufanov.     

Energetics and growth kinetics of a deep Prochlorococcus spp. population in the Arabian Sea

During the US JGOFS process studies in the Arabian Sea (1995), secondary fluorescence maxima (SFM) were observed frequently at the oxic–anoxic interface at the extreme base of the euphotic zone. These secondary peaks were most prominent during the early NE monsoon in the central oligotrophic portion of the Arabian Sea, although they were spatially and temporally variable. Based on high performance liquid chromatography (HPLC) and flow cytometry analyses, SFM were determined to be populated almost exclusively by the marine cyanobacterium Prochlorococcus spp. While SFM were about half the magnitude of primary fluorescence peaks, chlorophyll a biomass was typically an order of magnitude less than at the primary maxima (although total chlorophyll (a+b) differed only by a factor of two). Photosynthesis versus irradiance response curves revealed an efficient population adapted to extremely low light (∼0.02–0.05% surface irradiance) largely through increased light absorption capabilities. A theoretical spectral irradiance absorption efficiency model based on available spectral irradiance, individual cell properties, and bulk particulate spectral absorption also supports a well-adapted low-light population. Deck-incubated C-14 uptake as well as dilution growth experiments revealed instantaneous growth rates on the order of μ=0.01 d⁻¹. However, additional in situ observations suggest SFM populations may be more dynamic than the growth rates estimates from shipboard bottle incubations predict. We advance four hypotheses for the regulation of SFM populations including: (1) reduced loss rates, (2) discontinuous environmental conditions, (3) enhanced sub-oxic growth, and (4) physical mechanisms.     

太湖水中可溶性有机质,悬浮质和浮游藻类色素的光学特性的测定

本文着重分析了分光光度计测定的太湖水体中悬浮质、可溶性有机质和浮游藻类色素在可见光波段(400nm—700nm)的吸收;讨论了对池塘及两种高等植物色素吸收的对比测定;并利用迭代回归方法对测试样品的散射效应进行了订正。结果表明:(1)可溶性有机质吸收在短波部分较强;并且随着入射波长的增大,吸收几乎呈指数律减小,减小速率比国外海洋中的测量结果小。(2)水中悬浮质对光具有较强的散射作用,散射系数约按入射波长呈倒数变化。(3)不同植物中的色素的吸收光谱有明显差异。此外,利用所测数据,本文还对冬季太湖水体的反射光谱和向下光照衰减系数进行了数值计算,表明该水体对入射光照的反射和衰减与纯净水情况有很大差别,目此,太湖水光学特性研究中必须考虑水中物质的影响。     

The optical efficiency of flocs in shelf seas and estuaries

A correct understanding of the way in which light interacts with suspended particles is essential for quantitative interpretation of satellite visible band imagery of turbid shelf seas and estuaries. In this paper we describe new optical observations at 90 stations in the tidally energetic waters along the south and west coasts of Britain. The cross sectional area of the particles in suspension has been measured with a LISST laser diffraction instrument. Light scattering and absorption coefficients have been determined by applying Kirk’s method to radiometric measurements at 6 wavelengths. Results show that the scattering coefficient increases linearly with particle cross sectional area A per unit volume of water with a slope (scattering efficiency) of 1.96 (standard error 0.08) at 665 nm. Particle absorption coefficients a_P also increase with particle cross sectional area but at the most turbid stations, particle absorption per unit area (a_P/A) is observed to increase with the mean size of the particles in suspension. The particles are mostly mineral flocs which become more opaque as they grow larger and the photon path length through them increases. The implication of these results for remote sensing is that reflectance in the red part of the spectrum, which mainly depends on light scattering, is proportional to the cross sectional area of particles in suspension. Reflectance measurements in the green and blue parts of the spectrum, where particle absorption becomes more important, depend on the diameter of the particles as well as their cross sectional area. We show that simultaneous measurements of reflectance in the red and green parts of the spectrum can be used to derive both the area and size of the particles in suspension.     

Distinctive features of data processing for the side-looking radar of theSich-1 satellite

We show that the parameters of primary radar images obtained from theSich-1 satellite depend on the mode of survey and that the time dependence of the coefficient of correction of amplification in the channel of formation of radar signals is nonlinear. We propose to process radar images of the sea surface by using the so-called Bragg normalization of signals, which enables one to get a physically correct dependence of specific effective scattering surface on the elevation angle. We also consider a procedure of determination of the dependence of specific effective scattering surface of the sea on the wind velocity on the basis of the data accumulated by the side-looking radar of theSich-1 satellite. Translated by Peter V. Malyshev and Dmitry V. Malyshev     

基于EOF分析对南海西北海域水体光谱特性的研究

This study presents an analysis of the spectral characteristics of remote sensing reflectance(R_(rs)) in northwestern South China Sea based on the in situ optical and water quality data for August 2018.R_(rs)was initially divided into four classes,classes A to D,using the max-classification algorithm,and the spectral properties of whole R_(rs) were characterized using the empirical orthogonal function(EOF) analysis.Subsequently,the dominant factors in each EOF mode were determined.The results indicated that more than 95% of the variances of R_(rs) are partly driven by the back-scattering characteristics of the suspended matter.The initial two EOF modes were well correlated with the total suspended matter and back-scattering coefficient.Furthermore,the first EOF modes of the four classes of R_(rs)(A-D R_(rs)-EOF_1) significantly contributed to the total variances of each R_(rs) class.In addition,the correlation coefficients between the amplitude factors of class A-D R_(rs)-EOF_1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones.The spectral shape of class AR_(rs)-EOF_1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter(CDOM).The spectral shape of class B R_(rs)-EOF_1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM(a_g(λ)),whereas the spectral shape of class C R_(rs)-EOF_1 was governed by the back-scattering characteristics but not affected by the suspended matter.The spectral shape of class D R_(rs)-EOF_1 exhibited a relatively good correlation with all the water quality parameters,which played a significant role in deciding its spectral shape.