177
function is theoretically accounted for (via Mie theory), provided that the population of
scattering particles follows a Junge Law with an exponent value of 4 and if the mean relative
refractive index is close to 1.05 (Morel, 1973). Fluctuations around these values are rather
limited when correlation between experimental and computed VSF is sought. Incorporation
of a small minerogenic fraction (with n = 1.15) in order to more precisely explain the
backscattering lobe has also been suggested (Brown and Gordon, 1973; Zaneveld et al.,
1974). The direct counting (cf. 2.2) and the optical properties are thus in nice agreement, and
from this agreement it can also be concluded that the most plausible "mean" value for the
refractive index of marine particulates is about 1.05 (cf. 2.1). This result supports the
adoption of the Junge (Sheldon) size distribution as an operational hypothesis to analyze the
formation of the bulk scattering coefficient.
With this size distribution function (Eq. 5, with j = 4), the contribution of the different
classes of particles to the total scattering coefficient can be assessed. For the entire population,
b is expressed according to the following equation (similar to 20, but for scattering)
(24)
where d can replace p in Qb(P) , as soon as n and A have been fixed (1.05 and 421 nm
respectively, leading to p = d); F(d) is the size distribution function supposedly defined
between a lower and upper limit (dmin, d max ). By using the Junge distribution and omitting the
constant term, it becomes
(24')
where Sb(d) expresses the scattering cross section of all particles having the size d. With the
behavior of Sb already described (Fig. 5), it is easy to see that the above integral converges
toward a finite value when dmin -> 0, provided thatj < 7, and also strictly converges even
for an infinite number of particles (when d max - > 00), provided thatj > 3. The progressive
values of the above integral, whenj is made variable between 3.2 and 5, are shown in Fig.
9 as a function of d. The different curves indicate the sizes for which a certain percentage of
b is attained. For instance, with the exponent j = 4, the particles below 0.3 j.(m contribute
less than 5 % of b, half of the scattering is due to particles smaller than about 1.4 j.(m, and
function is theoretically accounted for (via Mie theory), provided that the population of
scattering particles follows a Junge Law with an exponent value of 4 and if the mean relative
refractive index is close to 1.05 (Morel, 1973). Fluctuations around these values are rather
limited when correlation between experimental and computed VSF is sought. Incorporation
of a small minerogenic fraction (with n = 1.15) in order to more precisely explain the
backscattering lobe has also been suggested (Brown and Gordon, 1973; Zaneveld et al.,
1974). The direct counting (cf. 2.2) and the optical properties are thus in nice agreement, and
from this agreement it can also be concluded that the most plausible "mean" value for the
refractive index of marine particulates is about 1.05 (cf. 2.1). This result supports the
adoption of the Junge (Sheldon) size distribution as an operational hypothesis to analyze the
formation of the bulk scattering coefficient.
With this size distribution function (Eq. 5, with j = 4), the contribution of the different
classes of particles to the total scattering coefficient can be assessed. For the entire population,
b is expressed according to the following equation (similar to 20, but for scattering)
(24)
where d can replace p in Qb(P) , as soon as n and A have been fixed (1.05 and 421 nm
respectively, leading to p = d); F(d) is the size distribution function supposedly defined
between a lower and upper limit (dmin, d max ). By using the Junge distribution and omitting the
constant term, it becomes
(24')
where Sb(d) expresses the scattering cross section of all particles having the size d. With the
behavior of Sb already described (Fig. 5), it is easy to see that the above integral converges
toward a finite value when dmin -> 0, provided thatj < 7, and also strictly converges even
for an infinite number of particles (when d max - > 00), provided thatj > 3. The progressive
values of the above integral, whenj is made variable between 3.2 and 5, are shown in Fig.
9 as a function of d. The different curves indicate the sizes for which a certain percentage of
b is attained. For instance, with the exponent j = 4, the particles below 0.3 j.(m contribute
less than 5 % of b, half of the scattering is due to particles smaller than about 1.4 j.(m, and