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Abstract
The laser remote sensing (lidar) technique of the atmosphere is a very efficient tool to monitor the aerosol optical and microphysical properties in the troposphere. In the frame of the EARLINET-ASOS project (2006-2011) a multi-wavelength (355-532-1064-387- 607 nm) Raman lidar station has been operated since March 2006 in Athens (37°98' N, 23°77' E, 200 m above sea level-asl.), Greece, at the Campus of the National Technical University of Athens (NTUA). To optimize the optical performance of our lidar system, as well as the quality of the aerosol measurements, mainly in the near-field (i.e. in the lower troposphere), several quality assurance (QA) tests have been adopted in the frame of the EARLINET-ASOS project. Through an optical design code, we were able to simulate the ray-tracing of the laser backscattered signals acquired at various wavelengths (in the present work mainly the 532 nm wavelength is presented). Simulating the light paths through the different parts of the lidar receiving optics (i.e. the receiving telescope, the transmitting optical fiber, the wavelength separation box with the dichroic beamsplitters, the collimating optics, the interference filters and the photodetectors (PMTs: photomultiplier tubes and APD: avalanche photodiode at 1064 nm)), we were able to discriminate the differences between the theoretical values of the full overlap distance with the real ones of our lidar system. Starting from the current design of our lidar system, we were able to propose a solution, enabling us to decrease the distance of the full overlap (DFO) down to values of the order of 600-800 m, instead of the existing DFO values of 1200-1500 m, using a programming code based on the Zemax© optical design tool.