Distribution of suspended matter in a coastal upwelling area. Satellite data and in situ measurements

Oceanographic measurements and satellite images recorded during the same period show that the data from the visible wavelengths of channel 1 and 2 of the AVHRR sensor (satellite NOAA-11) can be used to establish the distribution of total suspended particulate matter (TSPM) on the inshore continental shelves. The near-infrared channel (C2 = 725–1100 nm) is used for atmospheric corrections of channel C1 (580–680 nm) when concentrations in TSPM are low. However, when TSPM are high, they influence the channel C2 data. In this case, we use a subtraction between C1 data and a C1 value as constant. The fit function obtained between the TSPM measured by filtration and the corrected satellite reflectances is relatively linear for the low concentrations. This fit function permits to attribute an estimated concentration value to each satellite reflectance. In the Bay of Biscay, the additional use of a multiparameter probe and of AVHRR/NOAA-11 infrared data (channels 4 and 5, thermic infrared) makes it possible to show the presence of a coastal upwelling. The cold water rises to the surface near the coast. It is enriched in suspended matter, both removed by the waves and discharged by the rivers. These waters are then driven westwards, by the tidal currents and the continental northerly winds. The observation of complementary data showed that the coastal upwelling was active during the entire summer period of 1989 and possibly contributed to the cooling of coastal waters.