SOUTHERN-HEMISPHERE TROPOSPHERIC AEROSOL BACKSCATTER MEASUREMENTS - IMPLICATIONS FOR A LASER WIND SYSTEM

Values of backscatter coefficient at 0.532-mu-m, 0.694-mu-m, and 10.6-mu-m were determined both by direct measurement and by Mie computation from measured aerosol microphysical properties in the eastern Australian region from 4-degrees-S to 41-degrees-S. Volume backscatter coefficients at 10.6-mu-m were typically in the range 1 x 10(-11) to 3 x 10(-11) m-1 sr-1 for both approaches, although the experimental uncertainty in both cases was quite large. Agreement between the shorter wavelength lidars and the aerosol data was typically within the combined experimental uncertainties, although direct measurements were systematically larger than values derived from the aerosol data; individual regions were observed where the disagreement was larger than the combined error. Backscatter at 10.6-mu-m and at visible wavelengths was found to be sensitive to essentially different regions of the aerosol size spectrum, questioning to some degree the validity of using short-wavelength extinction and backscatter data to infer the global distribution of backscatter at wavelengths around 10.6-mu-m. Considerable day-to-day variability in backscatter was observed at all wavelengths. The implications of the very low backscatter values found, compared to northern hemisphere values, should be considered in the design of the Laser Atmospheric Wind Sounder (LAWS).