Remote sensing of atmospheric aerosols from active and passive optical techniques

Significant contributions to studies in aerosol science have come from optical remote sensing techniques and, for several reasons, these studies have special importance over the tropics where convective and high-altitude convective (as well as dynamical) processes affect the distribution of aerosols. Atmospheric aerosol studies employing active remote sensing techniques such as light detection and ranging (lidar) have been in progress for the past decade at the Indian Institute of Tropical Meteorology (IITM), Pune ( 18 degrees 32' N, 73 degrees 51'E, 559 m above mean sea level), India. Simultaneous measurements of aerosol optical and physical properties using passive remote sensing techniques such as spectroradiometry have also been in practice at the IITM since 1992. The experimental techniques developed and the results of the studies that have been carried out at the IITM are reviewed in this paper. These observations have enabled the study of aerosol climatology over Pune and have led to a better description of the atmospheric aerosol structure and stratification in the nocturnal atmospheric boundary layer, the air quality, and their association with the experimental terrain and meteorological conditions of the observing station. Such tropospheric aerosol climatologies are sparse over the tropics and almost nonexistent in India. The stratospheric physical and dynamical aerosol aspects of recent major volcanic eruptions, studied from ground-based lidar and satellite observations, are also discussed.