Coastal upwellings
Coastal upwelling could also be revealed using the algorithm defined
for coastal waters (Table II). On September 28th 1979 (Fig. 4) such upwellings
are visible near the Cap d'Agde. Presence of these upwellings in this area
have been accounted for (Millot, 1979) by the influence of continental winds
blowing from the shore. Under this influence, warm waters are rejected off-
shore superficially and upwelling of deep colder waters is produced. These
waters are rich in nutrients and their upwelling is revealed by remote sensing
as areas of higher chlorophyll content.
Figure 4: Coastal upwellings on the image of Nimbus-7 CZCS, September 28th
1979 revealed from the ratio R54.
It appears from the present report that the dynamic study of frontal
boundaries in the Gulf of Lions can be analyzed through remote sensing in the
visible spectrum. This is based on relative chlorophyll content of waters. Once
path radiance has been removed, appropriate algorithms are implemented to eval-
uate chlorophyll content. Using an algorithm adapted to the analysis of coastal
waters, outflow of the Rhone river and coastal upwellings have been delineated.
The presently described algorithms have been extensively truthed during
the NASA Nimbus-7 Experiment Team Cruise (Austin, 1980; Gordon et al., 1980).
It appears that the chlorophyll concentration values derived from these algori-
thms seem to be lower than those actually measured from vessels although its
estimation is good within a magnitude of 2 (Gordon et al., 1980). This is not
a major caveat when one is concerned mainly with relative chlorophyll distribu-
tion rather than precise quantitative measurement of this pigment.
As a whole, it appears from the present study that remote sensing in
the visible spectrum can indeed permit a dynamic study of frontal boundaries
in the sea.
Acknowledgements:
We wish to acknowledge the support provided by NASA Contract NAS-5-26
249 and NOAA/NESS grant NA80AA-D-00007.
694
Tree X d =
NE A A RT
EEE
Au
Ca
Ga
GC
Hg
Hc
Y
