**7. Conclusions**

370 Advanced Photonic Sciences

presence of dense aerosol layers, most probably - water aerosol (fog or orographic clouds near

the surface). The available meteorological data for the day support this conclusion.

Fig. 11. Schematic view of the lidar experiment over complex terrain; WS – wavelength separator; A1 and A2 – aerosol channels at 1064 nm and 532 nm, respectively; R – Raman

a) b)

Fig. 12. a) Time-averaged profiles of aerosol backscattering coefficient at the two wavelengths of measurement; b) Backscattering-related Ångström exponent profile.

anthropogenic origin, as typical for urban areas under dry atmospheric conditions.

The backscatter-related Ångström exponent defined in Eq.(19) is used as a qualitative indicator of aerosol particle properties. In Fig.12b, the range profile of BAE is presented, corresponding to aerosol backscatter profiles shown on Fig.12a. As one can see, the values of

 vary within the range 0.5-1.25 for distances of up to 5 km (plain zone). These values indicate for prevalence of the fine-mode aerosol particle fraction, most probably of

Around the plain-to-mountain interface zone located about 5.5 km away from the lidar station, BAE values approach zero indicating for prevailing contribution of the coarse-mode

channel at 607 nm.

aerosol fraction.

Various lidar technologies have been developed since the first lidar demonstration more than 40 years ago. In this chapter we presented some of the basic applications of lidars in the atmospheric research. The high informativity of lidar probing is due to the strong interaction of optical waves with atmospheric particles – aerosols and molecules, combined with range-resolved acquisition of lidar signals. The fast spread of lidars all over the world in the last two decades led to their organizing in regional lidar networks as EARLINET (Europe), MPLNET (USA), AD-Net (Japan), etc., integrated now in the Global lidar network (GALION). As lidars are practically the only instruments for high resolution vertical atmospheric profiling, their further improvement is one of the most important tasks for the lidar community. One of the ways to enhance the quality of lidar output information and its significance for the global and regional atmospheric monitoring is the creation of complex multispectral lidar systems, capable to provide more detailed and reliable data for the retrieval of aerosol optical, microphysical, and radiative properties, etc. This approach requires the development of novel more effective inverse algorithms, as well. It is also expected the future lidar networks to operate in a close cooperation with other existing networks as the sun-photometer network, groundlevel in-situ aerosol monitoring networks, satellite measurements (lidar and multispectral radiometers), radars, etc. The synergy resulting from such cooperation was demonstrated in a large number of experiments. The expected increase of the lidar station density all over the world is a good indication for their great significance in analysing local and global atmospheric processes and trends. In this connection we note the European project ACTRIS (Aerosols, Clouds, and Trace gases Research InfraStructure Network (www.actris.net)). Started in 2011 under 7-th Framework Program, it integrates the EARLINET, EUSSAR, CLOUDNET, and a new trace gas network into single-coordinated ground-based networks, with monitoring impact on the climate changes, air quality, and long-term transport of pollutants.
