The Black Sea IOPs based on SeaWiFS data

In this study, a regional algorithm for retrieving Inherent Optical Properties (IOPs) has been developed for the Black Sea using remote sensing reflectance at five wavelengths in the visible spectral range corresponding to the Sea-viewing Wide Field of View Sensor (SeaWiFS). The model retrieves a spectral signature of particle backscattering coefficient at 555 nm, bbp(λ), and its spectral slope, np, total absorption coefficient of colored detrital matter (sum of colored dissolved matter and non-algal particles, CDM) at 490 nm, aCDM(λ), spectral slope of CDM absorption coefficient, S, and chlorophyll a concentration, Ca. These satellite derived set of IOPs and bio-optical properties measured in situ in the western open Black Sea within period 1998-1999 have been analyzed. The result reveals four specific cases corresponding to 1) variation of spectral slope of CDM absorption coefficient, 2) coccolithophores blooms, 3) domination of micro-celled phytoplankton (diatoms and/or dinoflagellates) and 4) presences of the picoplankton in phytoplankton community. Examples of the spatial distribution and seasonal variability of the retrieved parameters in half-monthly composite maps are presented. A complete set of these maps for SeaWiFS lifetime is available on http://blackseacolor.com/.

" it was fifteen years ago today ... there is no doubt that this data set will continue to provide new discoveries and insights into the workings of this incredible planet that we call home." From Gene Feldman to ocean-color community

Background
Lately substantial advance has been attained on remote sensing methods for the inherent optical properties (IOPs) and applications of IOPs in ecosystem models. Their detailed description summarizes in [IOCCG, 2006]. Below the short description of remote sensing method for the Black Sea IOPs has been done. This method allows retrieving extended set of IOPs and recognizing the regional optical properties of the seawater.

Method and Results
A regional algorithm of IOPs, such as particle backscattering coefficient at 555 nm, spectral slope of particle backscattering coefficient, absorption coefficient of sum of colored dissolved organic matter and non-algal particles (CDM) at 490 nm, spectral slope of CDM absorption coefficient, and chlorophyll a concentration derived from SeaWiFS level-2 data, after proper flag/mask and spatial/temporal binning procedures, has been developed. The solution was retrieved in each node of the grid by iteration. To improve the stability of the solution, each iteration consisted of three steps (Table 1 and Fig. 1, Appendix). At each step, the different components of the IOPs were retrieved using data from different spectral bands. The key step is the first in the Table 1. To calculate the chlorophyll a concentration and CDM absorption coefficient, the regional algorithm developed for the Black Sea [Suslin et al., 2008a[Suslin et al., , 2008b Fig. 3. It has been shown that the optical properties of seawater in the Black Sea are typical waters classified as case 2. This means that in general there are no significant correlation values not only between the particle backscattering coefficient and CDM absorption coefficient, but also between the phytoplankton absorption coefficient and CDM absorption coefficient.

Application example
The obtained data set of IOPs can be applied to classify different phytoplankton types and other applications regarding an estimation of the Black Sea ecosystem indicators such as the downwelling diffuse attenuation coefficient , the euphotic depth [Churilova et al., 2009], water heating [Dorofeev et al., 2011] and etc. Below one application is considered. In the plane of the spectral slopes (the absorption coefficient of colored detrital matter and particle backscattering coefficient) derived from SeaWiFS data, the features of optically active components contained in seawater of the Black Sea (in particular, taxonomic and cell-size structure of phytoplankton) are presented in . For joint analysis, the in situ measurements of bio-optical characteristics of phytoplankton during two-year monitoring (from 1998(from to 1999(from [Curilova et al., 2004) in western part of the Black Sea and IOPs data set derived from SeaWiFS were used. At least four interesting situations related to (1) decreasing of the spectral slope value of the absorption coefficient of colored detrital matter in photolysis of colored dissolved organic matter or detritus impact, (2) increasing the the spectral slope value of particle backscattering coefficient during coccolithophorid blooms accompanied by the release of nano-size plates called coccoliths which well scatter the light in back part of volume scattering function, (3) low values of the spectral slope of particle backscattering coefficient when the predominance of micro-size phytoplankton (diatoms and dinoflagellates or their composition) occurs, (4) presumably with the presence of cianobacterias contained pigments which absorb light in the range from 530 nm to 560 nm, have been identified (see Fig. 5). Examples of the spatial distribution and seasonal variability of these features in half-monthly maps are given in Fig. 6. A complete set of halfmonthly and half-month climatology maps during SeaWiFS lifetime is available from [Black Sea BIO maps, 2012]. Thus, under certain conditions, a set of points in two-dimensional space of the spectral slopes identifies the optically active substances contained in seawater, in particular, the different phytoplankton types.

Conclusions
A regional algorithm of the inherent optical properties, IOPs, such as particle backscattering coefficient at 555 nm, spectral slope of particle backscattering coefficient, absorption coefficient of sum of colored dissolved organic matter and non-algal particles at 490 nm, spectral slope of CDM absorption coefficient, and chlorophyll a concentration derived from SeaWiFS level-2 data, has been developed.
It has been shown that the optical properties of seawater in the Black Sea are typical waters classified as case 2. This means that in general there are no significant correlation values not only between the particle backscattering coefficient and CDM absorption coefficient, but also between the phytoplankton absorption coefficient and CDM absorption coefficient.
Under the certain conditions, a set of points in two-dimensional space of the spectral slopes of IOPs identifies the optically active substances contained in seawater, in particular, the different phytoplankton types.
A complete set of IOPs and BIO half-monthly climatology and half-monthly maps during SeaWiFS lifetime is available from http:// blackseacolor.com [Black Sea IOPs maps, 2012;Black Sea BIO maps, 2012].
where nLw  is normalized water-leaving radiance at  , R RS  is above-surface remote sensing reflectance at  , F 0  is solar constant at band  where r RS is subsurface remote sensing reflectance, where b bp =b bp ⋅ 555   n p is particle backscattering coefficient,  is in nm, n p 0 is a spectral slope of b bp  , b bw is clear seawater backscattering coefficient.
a=a w a CDM a ph , where a w is clear seawater absorption coefficient, a CDM is sum absorption of dissolved and derital matter, a ph is phytoplankton absorption coefficient.
where  0 is 490 nm.   [Burenkov et al., 2000]) and satellite product R RS (λ) : (left) step-by-step evolution of model R m , RS (λ) spectrum of the first iteration (see Table 1) and (right) retrieved model R m , RS (λ) spectrum after third iteration