VERTICAL VARIATION OF EXTINCTION AND ATMOSPHERIC TRANSMISSION DUE TO AEROSOL-PARTICLES CLOSE ABOVE THE SEA-SURFACE IN THE MEDITERRANEAN COASTAL ZONE

The vertical variation of extinction and backscatter in the lowest par t of the atmospheric mixed layer is of considerable interest for the a ssessment of the performance of electro-optical systems, but is poorly known. Our purpose is to estimate the Vertical variation of extinctio n and atmospheric transmission due to aerosol particles near the air-s ea interface. Atmospheric extinction coefficients in the 3- to 5- and 8- to 12-mu m IR bands calculated using vertical aerosol distributions measured in the Mediterranean coastal zone are presented. The data re veal a negative extinction gradient between 1 and 2 to 3 m height duri ng winds of marine origin lower than 9 m/s, whereas a positive gradien t occurs between 1 and 2 to 3 m height during high-wind-speed periods (V greater than or equal to 9 m/s). A positive extinction gradient is also noted for vertical profiles recorded during moderate continental winds. These extinction gradients result in a relative difference in a tmospheric transmission between two sample heights that reach 60% in b oth the 3- to 5- and 8- to 12-mu m bands for an optical path of 10 km during high-wind-speed periods. These observed differences cannot be e xplained by current models to predict the vertical aerosol distributio n. (C) 1998 Society of Photo-Optical Instrumentation Engineers. [S0091 -3286(98)01706-1].