Observed effects of particles nonsphericity on the retrieval of marine and desert dust aerosol optical depth by lidar

Polarization lidar observations of maritime and Saharan dust aerosols collected at Crete (35.5°N–23.7°E) during the May 1999 PAUR II campaign are discussed. Lidar traces are inverted and integrated to provide aerosol optical depth at 532 nm. Two model relationships linking together aerosol backscatter and extinction coefficients are employed to perform such an inversion: one obtained employing the Mie theory, i.e., considering both maritime and dust particles as spheres, and a second one obtained by modeling dust particles as spheroids. The resulting two sets of aerosol optical depths are then compared to the ones measured by two independent, ground-based sunphotometers. These comparisons show that a good agreement exist between both lidar inversions and photometer-derived aerosol optical depths. However, the lidar retrieval employing the nonspherical model leads to a better agreement with photometric data when desert dust is observed. Average lidar–sunphotometer aerosol optical depth differences range between 12% and 24%. These values are comparable and sometimes smaller than ones observed to occur between the two sunphotometers employed in this exercise.