An airborne high spectral resolution lidar based on an iodine absorption filter

Kurzfassung

Aerosols directly influence the fluxes of solar and terrestrial radiation within the atmosphere by absorption and scattering of light. The quantification of this effect accounts for accurate determination of the aerosol’s optical properties. With conventional backscatter lidars climatically relevant aerosol properties like aerosol extinction can only be derived by inverting the lidar signal under the assumption of a a priori known lidar ratio, which generally is a highly variable quantity. For mineral dust, which is one of the major constituents of the tropospheric aerosol, lidar ratios ranging from 50 - 80 sr have been measured. Uncertainties in the lidar ratio will consequently lead to large errors in the retrieved optical properties. A well calibrated high spectral resolution lidar, HSRL, allows the direct determination of optical depth and extinction as described below. We have developed an airborne HSRL based on an iodine vapor absorption filter and a high power, frequency doubled Nd:YAG laser. The instrument was successfully employed during the Saharan Mineral Dust Experiment, SAMUM in May/June 2006 in Morocco to measure the optical properties of desert dust. With our measurements the Saharan dust can be characterized with regard to its lidar ratio, depolarization ratio and infrared-to-green backscatter ratio.