Extinction Profiles in the Lower Boundary Layer: Backscatter Lidar System Techniques

Abstract

In the lowermost part of the atmosphere, the boundary layer, the amount of aerosols is high. Aerosols interact with incoming irradiation from the sun. This interaction is called extinction, which means scattering and absorption. Due to that interaction light loses a part of the intensity when it passes a certain distance in the atmosphere. The amount of lost intensity depends on the aerosol distribution. In a solar power plant light that is coming from the sun is reflected by a field of heliostats (flat mirrors) and concentrated on a receiver, which is situated on a tower. This happens in the lowermost part (about 100 m or even up to 250 m) of the atmosphere. The amount of aerosols is high and therefore it has to be found out if extinction processes are as well. The influence of aerosols on the efficiency of a solar power plant is undetermined. Depending on the size of a field of heliostats, the distance to the receiver differs and so does the amount of extinction. For plant design the knowledge of extinction in the lower boundary layer is useful. One approach to estimate the loss of energy due to extinction is the Pitman and Vant-Hull model [21], that assumes that aerosol decreases exponentially with height. This is valid only for specific atmospheric conditions. In order to measure extinction profiles elastic backscatter lidar systems can be used. The challenge of such a lidar is that, due to the narrow laser beamwidth and the separation distance between emitter and receiver, data acquisition delivers incomplete information below the so-called full overlap height. An improvement of this information is needed. To correct this effect, several attempts have been made yet. A comparison of these techniques is needed to select the best ones for the given conditions and purposes to correct this effect. In this thesis the first step of comparing techniques to correct the lidar signals in the region close to the surface is made. Therefore three techniques have been applied to single datasets of measurement and compared.