T

he aerosol in the troposphere and the Planetary Boundary Layer (PBL) plays an important role in a number of atmospheric phenomena, air quality, cloud formation, radiation balance and chemical processes. The aerosol is also a convenient tracer in the observation of the PBL development. The backscatter lidar is already an established tool for continuous aerosol profiling, where a long-term experience is accumulated in both case studies and routine network observations.

The lidar is a single-wavelength, backscatter-depolarization instrument. The block diagrams of the optical and electronic parts are presented respectively in Figs.1 and 2. The specifications of the subsystems are given in Table 1.

Table 1
Table 1 - Specifications of micro-pulse lidar.


The lidar is assembled in a box, as shown in Fig. 3. Outside of this box are the computer for operation control and, if necessary, an air-cooling unit.

The development of the lidar and its adaptation for measurements in the PBL and lower troposphere, emerges from a similar lidar development for airborne operation. From its airborne predecessor, the reported instrument inherited the compact and robust design, and the stable alignment. The lidar is compact and mounted in an environmental protection box (54cm * 58cm * 58 cm), what makes it convenient for transportation to remote campaign sites. The data acquisition and the house-keeping electronic systems are controlled by a microprocessor, and an embedded PC is used to control the lidar measurements and to temporarily store before transmitting the collected data to the server.

Figure 1
Figure 1 - Block-diagram of the optical part of the micro-pulse lidar.

The alignment of the lidar is performed before placing it in the environmental housing. Thanks to its small size, its alignment may be performed when it is oriented in horizontal or slant directions towards convenient hard targets. The signals used to control the alignment in our practice are, once corrected for range, the returns from local hills at approximately 2 km, 4 km and 8 km, respectively, increasing in a sequence. During the procedure, apertures with different diameters are placed in front of the receiver. The alignment is controlled by maximizing the received signal from the same target and by its proportionality to the area of the apertures. The stability of the alignment after placing the lidar in its environment box is achieved by two means: first, by the specific design of the output mirror control mechanics; second, by temperature stabilization of the overall lidar structure inside the environmental housing.

Figure 2
Figure 2 - Block-diagram of the electronic part of the micro-pulse lidar.

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