The altitude profile of the effective radius, reff, of atmospheric boundary layer aerosols was retrieved from simultaneous twowavelength lidar measurement near Manila Bay. The effective radius was retrieved using a simple method that makes use of the angstrom coefficient, ?, obtained from the extinction coefficients at the two wavelengths. The altitude profiles of the extinction coefficients at 532-nm and 1064-nm lidar wavelengths were obtained using Femald's inversion algorithm combined with Klett's boundary value algoritlun. used to obtain the aerosol extinction coefficient at the reference height. Assuming a lognonnal size distribution. with a geometric standard deviation of 1 .54, for atmospheric boundary layer aerosols. and a constant refractive index of 1.45 - Oi, the angstrom coefficient is determined at different mode radius, rg, using Mie Scattering Theory. A curve fitting analysis using the method-of-least-squares is done on the theoretical value of ? to obtain a sixth-order polynomial equation that gives the dependence of ? with rg. The altitude profile of reff is retrieved by using the measured value of ? into the equation. This method was applied to actual lidar experiments and the effective radius of the atmospheric boundary layer aerosols was observed to vary between 0.26 ?m to 0.29 ?m within the layer.
KEYWORDS: LIDAR, Clouds, Aerosols, Atmospheric modeling, Mass attenuation coefficient, Signal attenuation, Signal to noise ratio, Nd:YAG lasers, Lanthanum, Signal detection
Simultaneous two wavelength LIDAR measurements of clouds and boundary layer aerosols were performed near Manila Bay. Philippines. The two-wavelength LIDAR system employs the simultaneous outputs at 1064-nm (420 mJ) and 532-nm (175 rnJ) of a Q-Switched, 20-Hz Nd:YAG laser and a 203 .20-mm diameter Schmidt Cassegrain telescope set for 1-mrad field-of-view. The vertically-pointing, biaxial Mie LIDAR facilily became operational early last year and is in the STRC building (14.339°N, 120.595°E) of De La Salle University (DLSU), Taft Avenue, Manila. LIDAR measurements were obtained in 1-minute intervals from 0812-0830 hours (local time) on December 20, 1999 and 0650-0930 hours (local time) on March 23. 2000. Extinction coefficients for these boundary layer aerosols and clouds were computed using Klett's modified inversion algorithm. The extinction coefficients for the clouds observed on December 20 were 20 —100 km-1 (1064 nm) and 5 — 40 km-1 (532 am). Boundary layer aerosols found on the same day had extinctions of 10 km-1 for both wavelengths and reached up to 300 m above the site. The March 23 data show mostly boundary layer aerosols from 200 — 600 in above the LIDAR having extinction values of 6 —8 km-1 for both wavelengths.
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