176
empirical relationship (Gordon and Morel, 1983), based on the analysis of about 500 coupled
observations (in the world ocean and after the turbid - Case 2 waters have been excluded) is
b- 0.30 ( ± 0.15)o.62
(23a)
where the coefficient 0.30 is a mean value which acknowledges that a certain flexibility occurs
in such a "natural" law, yet limited to oceanic waters (the upper value for this coefficient
(0.45) corresponds to the transition between Case 1 and turbid-Case 2 waters). By noting that
Eq. 23a can be transformed into
_b_ -O.30 -0.38
(23b)
it appears that bl < C>, (formally equivalent to b" in Eq. 22), depends on the biological state
of the water and increases with decreasing C concentration. For instance, when C goes from
0.02 to 20 mg m- 3 , b varies from 0.027 to 2 mol, therefore bl decreases from 1.33
to 0.10 m 2 (mgt'.
The non-linear character of Eq. 23 with respect to the pigment concentration originates
from the fact that all suspended material (living + detrital), is responsible for the formation
of b; b has been found to be roughly proportional to the total particulate organic carbon
(Morel, 1988). The exponent lower than 1 in Eq. 23a indicates that the non-algal compartment
has, in comparison to the algal compartment, an increasing importance when C diminishes.
The ChI-specific scattering coefficient b" is a lower limit for bl < ChI> , attainable only in the
absence of detritus. The compatibility of these two parameters has been discussed elswhere
(Morel, 1987). For diminishing phytoplankton biomass, the increasing role of biodetritus (and
of small, not easily-observable organisms) results in an increase of bl< ChI>.
Another important and relatively old experimental finding deals with the volume scattering
function. It was found that the phase function for particles is surprisingly stable in various
marine situations. This conclusion was first reached in 1968 (Jerlov) and has always been
found to be true, even if the shape of the VSF was found slightly variable in the backward
directions (where measurements admittedly are more questionable). The phase function for
marine particles as determined by Petzold (1972) is often used for modeling purposes (Kirk,
1981; Gordon, 1989) as being of ubiquitous significance. Interestingly, the shape of this phase
empirical relationship (Gordon and Morel, 1983), based on the analysis of about 500 coupled
observations (in the world ocean and after the turbid - Case 2 waters have been excluded) is
b- 0.30 ( ± 0.15)
(23a)
where the coefficient 0.30 is a mean value which acknowledges that a certain flexibility occurs
in such a "natural" law, yet limited to oceanic waters (the upper value for this coefficient
(0.45) corresponds to the transition between Case 1 and turbid-Case 2 waters). By noting that
Eq. 23a can be transformed into
_b_ -O.30
(23b)
it appears that bl < C>, (formally equivalent to b" in Eq. 22), depends on the biological state
of the water and increases with decreasing C concentration. For instance, when C goes from
0.02 to 20 mg m- 3 , b varies from 0.027 to 2 mol, therefore bl
to 0.10 m 2 (mgt'.
The non-linear character of Eq. 23 with respect to the pigment concentration originates
from the fact that all suspended material (living + detrital), is responsible for the formation
of b; b has been found to be roughly proportional to the total particulate organic carbon
(Morel, 1988). The exponent lower than 1 in Eq. 23a indicates that the non-algal compartment
has, in comparison to the algal compartment, an increasing importance when C diminishes.
The ChI-specific scattering coefficient b" is a lower limit for bl < ChI> , attainable only in the
absence of detritus. The compatibility of these two parameters has been discussed elswhere
(Morel, 1987). For diminishing phytoplankton biomass, the increasing role of biodetritus (and
of small, not easily-observable organisms) results in an increase of bl< ChI>.
Another important and relatively old experimental finding deals with the volume scattering
function. It was found that the phase function for particles is surprisingly stable in various
marine situations. This conclusion was first reached in 1968 (Jerlov) and has always been
found to be true, even if the shape of the VSF was found slightly variable in the backward
directions (where measurements admittedly are more questionable). The phase function for
marine particles as determined by Petzold (1972) is often used for modeling purposes (Kirk,
1981; Gordon, 1989) as being of ubiquitous significance. Interestingly, the shape of this phase