Automatic Determination of Atmospheric Structures, Aerosol Optical Properties and Particle Type with the R-MAN510 Raman Dual-Polarization Lidar Super Ceilometer

Atmospheric particles have many impacts and interactions with climate, air quality and human activities. The improvement of chemistry transport and dispersion models forecasts requires the near real-time automatic profiling of atmospheric layers which can only be performed with active remote sensors. The horizontal spread and the vertical extend of aerosol layers can be measured with a network of ceilometers or elastic backscattered lidars. Nevertheless, additional information on aerosol sphericity (depolarization ratio) and optical properties (extinction-to-backscatter ratio) are necessary for an accurate characterization and an unambiguous classification of particle type.

For addressing these needs, a new Raman and dual polarized lidar super ceilometer (the R-MAN510) has been developed by Leosphere Company. This sensor combines the benefits of both ceilometers (low cost, hardiness and networking) and lidars (low overlap and high measurement range). This automatic and stand-alone ultraviolet lidar at 355 nm has been especially designed for network applications with a low-maintenance diode-pumped laser. It is composed of three detection channels for the elastic co- and cross-polarizations and for the inelastic Raman backscattered signal from nitrogen molecules at 387 nm. The detection of atmospheric structures (such as planetary boundary layer and residual layer heights, aerosol and cloud layers) is based on a vertical gradient method using the elastic channels of the lidar. The perpendicular channel is used for the retrieval of particle depolarization ratio which gives additional information on aerosol shape and sphericity. It is thus possible to highlight dust-like aerosols (desert dusts, volcanic ashes,…) and ice crystals in high altitude cirrus cloud which are characterized by high depolarization values. The nitrogen Raman channel of the lidar is crucial for the constraint of the elastic channel and the accurate retrieval of aerosol optical properties. Aerosol extinction and backscatter coefficients, extinction-to-backscatter ratio (or so-called lidar ratio LR) are thus retrieved with an uncertainty lower than 10%. This is an essential point as a reliable extinction coefficient profile is needed for the assessment of volcanic ash concentrations. By combining information on atmospheric structures and optical properties it is possible to discriminate and to classify aerosols layers (dusts, volcanic ashes, sea salt, continental pollution) and cloud layers (altocumulus, altostratus, cirrus).

We will present here some results obtained during recent campaigns involving R-MAN510 lidar systems. The lidar capabilities and performances will be discussed according to atmospheric conditions.