The authors previously reported an equation
μ=
aT-b, where
μ is extinction coefficient of incident light into a suspension,
T visible transparency depth of Secchi-disc and
a,
bconstants.
“
a” can be an index of the particle size, as far as “
b” remains to be a certain value though it varies by the quality of suspended material. In the sea water, the value of
b was recognized to be 0.3 in neritic and even in oceanic waters.
So “
a”, the suspension factor, of various sea regions can be comparable to each other and is observed to be a good indicator of the condition for the growth of filter-feeders there, and recently
a-Cl number, combined “
a” value with Cl‰, was showed to be a better index for it.
When
T can't be observed, “
a” is obtained as follows from the values of
μ and
τ, Turbidity, in situ.
Generally in the suspensions of such particles as their size is of the same order to the wave-length of incident-light or slightly larger, there is a relation
μ=
kSα, where
S is the concentration of particles,
α is a constant, 0.2 in sea waters, neritic and oceanic, and
k a parameter which varies with the value of “
a”, according to the relation
k=0.64
a-0.055.
While theoretically there is a relation
τ=
γS, where
γ is a parameter which varies with the particle diameter.
From these two eqs. we can obtain
μ=
k'
τ0.2, wrere
k'=
kγ-0.2. This relation was recognized to be in good fit with many data hitherto obtained actually by assuming
k'=0.72
a-0.04.
And we obtain
a=1.38
μτ-0.2+0.056
according to which “
a” can be obtained even by layers in the sea from
μ and
τ without
T. Applying the value of
γ computed theroretically by Burt under the condition that the wave-length is 550m
μ and refraction coefficient between particle and water 1.15, the diameters of particles by “
a” values were tried to obatin from the eq.
γ=(0.64
a-0.055/0.72
a-0.040)
5,
resulting the diameters of 2-5
μ in usual bay-waters in Japan, as shown in figures.
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