Aerosol extinction-to-backscatter ratio derived from passive satellite measurements
Spaceborne reflectance measurements from the POLDER instrument are used to study the specific directional signature close to the backscatter direction. The data analysis makes it possible to derive the extinction-to-backscatter ratio (EBR), which is related to the inverse of the scattering phase function for an angle of 180° and is needed for a quantitative interpretation of lidar observations (active measurements). In addition, the multidirectional measurements are used to quantify the scattering phase function variations close to backscatter, which also provide some indication of the aerosol particle size and shape. The spatial distributions of both parameters show consistent patterns that are consistent with the aerosol type distributions. Pollution aerosols have an EBR close to 70, desert dust values are on the order of 50 and EBR of marine aerosols is close to 25. The scattering phase function shows an increase with the scattering angle close to backscatter. The relative increase ∂ln P/∂γ is close to 0.01 for dust and pollution type aerosols and 0.06 for marine type aerosols. These values are consistent with those retrieved from Mie simulations.