SAFIRE ATR42: BASTALIAS L2 dataset

This product is based on ALiAS and BASTA data. This combined dataset was developed to take advantage of the lidar-radar synergy and complementarity to improve the detection of clouds, drizzle and rain. For this purpose, the two modes of the BASTA radar products are merged on a single horizontal grid and a single time resolution (1.5 s). Then the reflectivity is corrected for liquid and gas attenuation and the radar sensitivity is defined as a function of the distance from the aircraft. A first classification of hydrometeors is then made on the basis of radar observations. As the reflectivity associated with the presence of a remote hydrometeor depends on the drop diameter, reflectivity thresholds can be used to distinguish cloud droplets from drizzle or rain. The BASTALIAS dataset thus considers three options for the definition of cloud droplets, associated with each of these thresholds. The ALiAS lidar data at their original resolution are analyzed to determine the horizontal lidar profile that corresponds to the molecular or aerosol backscatter, to estimate the noise level, and to detect the presence of clouds. The lidar cloud detection methodology used in the BASTALIAS dataset is inspired from that developed for the CALIPSO space lidar and the airborne LNG lidar. This information is then used to define a lidar pseudo cloud mask at the same space and time resolution as the radar information. Finally, the lidar and radar cloud masks are analyzed jointly to make a final classification of hydrometeors and a lidar-radar cloud mask.