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the Lss
irically
, 1980;
e type:
Rij 1s
the ratio of Lg, in channels i and j and a and b are empirical constants. Diff-
erent values for i and j and constants a and b were used according to the type
of waters under study (Table II) (for review, see Sturm, 1980).
Table II: Algorithms used to derive chlorophyll contents (C) from Les values
C=aR72 , C in mg/m?
CZCS channels variable values
à j .à b
offshore 1 3 1.129 1.711
(C<1.5mg/m3) (443nm) (550nm)
coastal waters 2 3 3.326 2.439
(C>1.5mg/m3) (520nm) (550nm)
Mapping of phytoplankton in the Gulf of Lions
Data were obtained on CRT tapes (CZCS Radiances and Temperature tapes)
from the NASA. Images were analysed on several dates in 1979. A 256x256 pixel
matrix was extracted from the standard image. This matrix was centered at 43?N-
4°E and encompassed the Gulf of Lions. Processing of these data by the methodo-
logy described above allowed us to delineate frontal boundaries with oceanogra-
phic significance and to follow their change throughout 1979. We thus, confirmed
that the biomass of phytoplankton is a good indicator for the mesoscale distri-
bution of water masses.
Mesoscale cyclonic eddy in winter offshore from Marseilles
Figure 1 presents computerized imagery of data collected on April 13th
1979. The algorithm implemented used the ratio of Lg (443nm) to L (550nm). This
allowed the visualization of a mesoscale cyclonic eddy centered at^42952^N-5?12^7E
extending up to an approximate diameter of 50 km. No such cyclonic activity was
visible on raw data. To achieve optimal visualization of this phenomenon, diff-
erent colors were attributed to various ranges of chlorophyll concentration. The
cyclonic shape could be readily visualized using a single color for a narrow
range of chlorophyll-like pigments concentration around 0.27mg/m3 (Caraux,
Austin, 1982).
The presence of eddies in this area has already been reported by ocean-
ographic campaigns (Medoc Group, 1970; Seung 1980). This zone is under the in-
fluence of cold and dry continental winds. The cyclonic formation has been ac-
counted for by the baroclinic instability of waters at this time of the year
(Gascard, 1978). When the winter turbulences are fading, the phytoplankton which
has been supplied by nutrients from upwelling deep sea waters, develops in a
sudden bloom. As a consequence, the swirling features can be visualized by
remote sensing of chlorophyll.
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