Abstract
Abstract. The Two-Stream technique employs simultaneous measurements performed by two elastic backscatter lidars pointing at each other to sample into the same atmosphere. It allows for a direct retrieval of the extinction coefficient profile from the ratio of the two involved lidar signals. During a number of Alfred-Wegener-Institute (AWI) campaigns dedicated to Arctic research, the AWI's Polar 2 aircraft with the integrated onboard nadir-pointing Airborne Mobile Aerosol Lidar (AMALi) was utilised. The aircraft flew over a vicinity of Ny Ålesund on Svalbard, where the zenith-pointing Koldewey Aerosol Raman Lidar (KARL) has been located. This experimental approach gave the unique opportunity to retrieve the extinction profiles with a rarely used Two-Stream technique against a well established Raman technique. Both methods were applied to data obtained for clean Arctic conditions during the Arctic Study of Tropospheric clouds and Radiation (ASTAR 2004) campaign, and slightly polluted Arctic conditions during the Svalbard Experiment (SvalEx 2005) campaign. Successful comparison of both evaluation tools in different measurement conditions demonstrates sensitivity and feasibility of the Two-Stream method to obtain particle extinction and backscatter coefficients profiles without assumption of their relationship (lidar ratio). The method has the potential to serve as an extinction retrieval tool for KARL or AMALi simultaneous observations with the space borne CALIPSO lidar overpasses during the ASTAR 2007.
Highlights
Retrieval of the particle microphysical parameters, from lidar derived optical properties of particles in the atmosphere consists of a mathematically ill-posed inversion problem (Bockmann, 2001)
In this paper we present a study dedicated to the direct comparison of the Two-Stream particle extinction and backscatter coefficient profiles, and the lidar ratio profiles with the respective Raman retrievals
The applicability of the Two-Stream method depends critically on the constraint that both lidars probe into the same air masses
Summary
Retrieval of the particle microphysical parameters (particle effective radius, index of refraction and size distribution), from lidar derived optical properties of particles in the atmosphere (particle extinction and backscatter coefficient profiles) consists of a mathematically ill-posed inversion problem (Bockmann, 2001). Any inversion of microphysical parameters fed with both coefficients calculated independently is performed more precisely, especially for the determination of the particle size distribution (Muller et al, 1999; Veselovskii et al, 2002; Bockmann and Kirsche, 2006). Obtaining information on the particle extinction αpart(h) and backscatter βpart(h) coefficients without the often used assumption of their relationship signifies a great step forward in the interpretation of lidar data.
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