AEROSOL-PROFILE MEASUREMENTS IN THE LOWER TROPOSPHERE WITH 4-WAVELENGTH BISTATIC ARGON-ION LIDAR

The scattering properties of aerosols over a tropical urban station, Pune, India, (18 degrees 32' N, 73 degrees 51' E, 559 m above mean sea level), are studied with a bistatic, multiwavelength, continuous-wave, argon-ion lidar. The scattered-intensity profiles (up to 1000 m above ground level) measured at four wavelengths (0.4765, 0.4880, 0.4965, and 0.5145 mu m) of the laser during November 1987-March 1990 revealed certain spectral dependence, in conformity with the Mie theory of aerosol particles. Methods for retrieving the bulk as well as the height variation of aerosol-size distribution from the inversion of angular distribution of scattered-light-intensity measurements from a constant altitude and scattered-intensity vertical-profile measurements at different wavelengths are explained. Results obtained from these approaches are presented and compared with results reported by other investigators. The deviations in the results are discussed in relation to the assumptions involved and the terrain-atmospheric conditions at the experimental station. It is found that the aerosol-size-distribution parameter is altitude dependent beside its dependence on refractive index and wavelength of incident radiation. The results of the study suggest that the information content from bistatic, multiwavelength laser scattering measurements is useful for inferring aerosol-size distribution.