165
of larger a, the distance between the nearly parallel curves for SS and FS is governed by the
refractive index (decreasing distance for increasing n). Whatever a, the ratio FS/SS takes a
fixed value which is typical of n; the "rods" in Fig. 7b tend to be vertically oriented. In this
size range, FS could be seen as a measure of the geometrical cross section, whereas its
associated SS value could mainly indicate the refractive index value.
Any precise statement about the significance of SS and FS signals is always simplistic. The
log-log representation used in Fig. 7a and b also conceals and smooths some more
complicated patterns. A more systematic resort to theory and computations is certainly
possible and able to resolve many ambiguities.
PARTICLES AND BULK OPTICAL PROPERTIES OF A WATER BODY
The local inherent optical properties of an absorbing - scattering medium, namely: (1) its
absorption coefficient, a, (2) its scattering coefficient, b, and (3) its volume scattering
function, {3 (8), are strictly additive properties with respect to each component contributing
to the formation of the bulk coefficients (see e.g. Preisendorfer, 1961). It is therefore logical
to examine to what extent the optical properties of a water body can be explained in light of
the present knowledge concerning the particles it contains, at least those presently identified.
Besides particles, water itself and dissolved materials, there are also optical components not
considered in the scope of the present discussion. It would suffice to recall that the optical
properties (b; (3 (8); a) of optically pure sea water (water molecules and ions) are relatively
well established and theoretically understood (Morel, 1974; Smith and Baker, 1981). Their
spectral variations are also known, even though the absorption coefficient at its minimum (in
the blue part of the spectrum) is still difficult to ascertain. The effect of dissolved organic
compounds is also relatively well documented. They are introduced into the sea by land
drainage (and can be important in coastal zones influenced by rivers), or they can be locally
produced through the biological activity in the open ocean where they have a long residence
time. This dissolved organic matter globally acts as a "blue absorber" and, from an optical
viewpoint, it is identified as the "yellow substance". Many studies after that of Kalle (1938)
have concluded that the absorption spectrum exhibits a regular exponential increase from the
of larger a, the distance between the nearly parallel curves for SS and FS is governed by the
refractive index (decreasing distance for increasing n). Whatever a, the ratio FS/SS takes a
fixed value which is typical of n; the "rods" in Fig. 7b tend to be vertically oriented. In this
size range, FS could be seen as a measure of the geometrical cross section, whereas its
associated SS value could mainly indicate the refractive index value.
Any precise statement about the significance of SS and FS signals is always simplistic. The
log-log representation used in Fig. 7a and b also conceals and smooths some more
complicated patterns. A more systematic resort to theory and computations is certainly
possible and able to resolve many ambiguities.
PARTICLES AND BULK OPTICAL PROPERTIES OF A WATER BODY
The local inherent optical properties of an absorbing - scattering medium, namely: (1) its
absorption coefficient, a, (2) its scattering coefficient, b, and (3) its volume scattering
function, {3 (8), are strictly additive properties with respect to each component contributing
to the formation of the bulk coefficients (see e.g. Preisendorfer, 1961). It is therefore logical
to examine to what extent the optical properties of a water body can be explained in light of
the present knowledge concerning the particles it contains, at least those presently identified.
Besides particles, water itself and dissolved materials, there are also optical components not
considered in the scope of the present discussion. It would suffice to recall that the optical
properties (b; (3 (8); a) of optically pure sea water (water molecules and ions) are relatively
well established and theoretically understood (Morel, 1974; Smith and Baker, 1981). Their
spectral variations are also known, even though the absorption coefficient at its minimum (in
the blue part of the spectrum) is still difficult to ascertain. The effect of dissolved organic
compounds is also relatively well documented. They are introduced into the sea by land
drainage (and can be important in coastal zones influenced by rivers), or they can be locally
produced through the biological activity in the open ocean where they have a long residence
time. This dissolved organic matter globally acts as a "blue absorber" and, from an optical
viewpoint, it is identified as the "yellow substance". Many studies after that of Kalle (1938)
have concluded that the absorption spectrum exhibits a regular exponential increase from the