181
Backscattering coefficient
The backscattering coefficient, bb, is a crucial parameter to the extent that it governs the
reflectance of the ocean (see e.g. Morel and Prieur, 1977). The same empirical and analytical
approaches as above can be repeated with the aim of understanding the formation of the
backscattering coefficient of oceanic waters.
The backscattering ratio b i (defined as the ratio bib) is of the order of 2 % for oceanic
particulate matter (see e.g. Petzold, 1972 or Gordon, 1989). It has been actually obvserved
that b i in oceanic waters is not a stable parameter and would decrease from about 2 % in
oligotrophic waters down to about 0.2 % in eutrophic waters. For the purpose of modelling
the reflectance, an empirical relationship, which accounts for this decrease with increasing C
concentrations, has been proposed (Morel, 1988)
(26)
This expression combined with Eq. 23a (and letting A = 550 nm) is used to construct the
straight solid line in Fig. 11, representing the variations of bb along with the pigment
concentration.
The b i ratio for various algae have been experimentally determined (Bricaud et al., 1983;
Ahn, 1990). They prove to be within the 10-4 - 10- 3 range, as theoretically expected through
Mie theory (see in Morel and Bricaud, 1981b). After a shift by 3 orders of magnitude, the
b a lines of Fig. 10 are redrawn in Fig. 11. The b. ratio of marine bacteria has also been
measured (Morel and Ahn, 1990). It is higher than that of algal cells by at least one order of
magnitude. The typical bacterium (d = 0.55 mm and n = 1.05) theoretically has a b i ratio
of 1.1 % at 550 nm. Therefore the b m values in Fig. 10 are multiplied by 10- 2 in order to
estimate the contribution of microbes to the backscattering coefficient (dashed line in Fig. 11).
The contribution of bigger heterotrophs to bb can again be computed by using Eq. 24', where
Qb is now replaced by Qbb, the backscattering efficiency factor computed through Mie theory.
The comparison of the two partial integrals (from 0 to 0.7 j.tm, or from 0.7 j.tm to 00) shows
Backscattering coefficient
The backscattering coefficient, bb, is a crucial parameter to the extent that it governs the
reflectance of the ocean (see e.g. Morel and Prieur, 1977). The same empirical and analytical
approaches as above can be repeated with the aim of understanding the formation of the
backscattering coefficient of oceanic waters.
The backscattering ratio b i (defined as the ratio bib) is of the order of 2 % for oceanic
particulate matter (see e.g. Petzold, 1972 or Gordon, 1989). It has been actually obvserved
that b i in oceanic waters is not a stable parameter and would decrease from about 2 % in
oligotrophic waters down to about 0.2 % in eutrophic waters. For the purpose of modelling
the reflectance, an empirical relationship, which accounts for this decrease with increasing C
concentrations, has been proposed (Morel, 1988)
(26)
This expression combined with Eq. 23a (and letting A = 550 nm) is used to construct the
straight solid line in Fig. 11, representing the variations of bb along with the pigment
concentration.
The b i ratio for various algae have been experimentally determined (Bricaud et al., 1983;
Ahn, 1990). They prove to be within the 10-4 - 10- 3 range, as theoretically expected through
Mie theory (see in Morel and Bricaud, 1981b). After a shift by 3 orders of magnitude, the
b a lines of Fig. 10 are redrawn in Fig. 11. The b. ratio of marine bacteria has also been
measured (Morel and Ahn, 1990). It is higher than that of algal cells by at least one order of
magnitude. The typical bacterium (d = 0.55 mm and n = 1.05) theoretically has a b i ratio
of 1.1 % at 550 nm. Therefore the b m values in Fig. 10 are multiplied by 10- 2 in order to
estimate the contribution of microbes to the backscattering coefficient (dashed line in Fig. 11).
The contribution of bigger heterotrophs to bb can again be computed by using Eq. 24', where
Qb is now replaced by Qbb, the backscattering efficiency factor computed through Mie theory.
The comparison of the two partial integrals (from 0 to 0.7 j.tm, or from 0.7 j.tm to 00) shows