**5.2.
Algorithms**

In comparison
with the previous issue [6], the modified algorithms for calculation
of chlorophyll and suspended matter concentrations were used. They
were derived by using new *in
situ *data
obtained in the summer expeditions
of 2008-2009 in
the northern part of the Caspian Sea [37].

**Chlorophyll
concentration**

The regression equation for calculation of chlorophyll concentration from SeaWiFS data is similar to the previous one [6]:

*Chl = *0.732·[*L*_{wn}*(555)/L*_{wn}*(510)*]^{3.40},
(15)

where
*L*_{wn}*(555)*
and *L*_{wn}*(510)*]
are the normalized water-leaving radiances at 555 and 510 nm (*n
*= 55, *r*^{2}
= 0.708, the error is equal to 0.33
mg/m^{3}).

The algorithm to derive chlorophyll concentration from MODIS-Aqua data was simplified in comparison with [6]:

*Chl
*= 0.573 (*R*_{rs}(488)/*R*_{rs}(551)^{-2.39}.
(16)

where
*R*_{rs}(488)
and *R*_{rs}(547)
are the above-surface remote-sensing reflectance at 488 and 547nm,
respectively (*n *=
55, *r*^{2}
= 0.638, the error is equal to 0.41
mg/m^{3}).

**Particle backscattering and TSM**

First,
the particle backscattering coefficient *b*_{bp}*
*was derived from
the remote sensing reflectance corrected to the bottom reflection
[38].
TSM concentration was calculated by using
the regression equation between *TSM*
and the particle backscattering coefficient *b*_{bp
}:

*TSM*
= 67.1 *b*_{bp}*
*+ 0.554,
(17)

where
*TSM* is in
mg/l* *, *b*_{bp
} in m^{-1}
(n=42,
R^{2}
= 0.835, the regression error is 0.81
mg/l).

**Yellow substance absorption**

The
values of *a*_{g}
were calculated with the semi-analytic
algorithm as described in 4.2. The algorithm worked stably only for
the May-September period so the mean monthly distributions of the
*a*_{g}
values were calculated only for this
season.