Measurements of Aerosol Optical Parameters with Backscatter and Side-scatter Lidars

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Studies in Surveying and Mapping Science (SSMS) Volume 4, 2016

www.as-se.org/ssms

Measurements of Aerosol Optical Parameters with Backscatter and Side-scatter Lidars Huihui Shan1, Junjian Liu2, Hui Zhang1, Xiaomin Ma1, Zongming Tao1* Department of Basic Sciences, Army Officer Academy, Hefei, 230031, China

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Postgraduate Company, Army Officer Academy, Hefei, 230031, China

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*zmtao@aiofm.ac.cn Abstract The extinction coefficient, backscattering coefficient and phase function are essential optical parameters of aerosol. General backscatter lidar is an important tool for aerosol detection, but it has the blind area in near-range. Combining backscatter with side-scatter lidars, the above three optical parameters can be measured. Our experimental system is presented, three optical parameters retrieval methods are introduced, and three cases are studied. The results of case studies show that our lidars system and the retrieval methods work well. OCIS code: 010.1110, 280.3640, 290.5820 Key words Atmospheric Optics; Aerosol; Lidar; Aerosol Optical Parameters

Introduction Liquid and solid particles suspended in the atmosphere are entitled atmospheric aerosol. Their aerodynamic diameters are between 0.001μm and 100μm. Atmospheric aerosol is one of the current hot researches in atmospheric science, because it has a certain impact on human health and the global climate. Aerosol affects Earth’s radiation budget directly, and affects cloud-radiation interactions indirectly [1]. At the same time, aerosol is a part of the pollutants in the air. Air pollution often occurs on the layer of a few kilometers from ground which generally is referred to as the planetary boundary layer. Aerosol chemistry, concentrations and type change with altitude. In order to understand aerosol’s impact on the global climate change and air pollution control, aerosol vertical distribution monitoring is very important, so we need to get information of aerosol altitude profile [2]. So far, there are many methods to detect aerosol, such as sun photometer and remote sensing techniques. Using sunlight, sun photometer provides the total aerosol properties integrated through the entire atmosphere. Backscatter lidar provides aerosol backscattering altitude profile, so it becomes a powerful tool for detection of atmospheric aerosol [3]. Due to backscatter lidar transmitters and receiver’s field of-view (FOV) in the same place, backscattering light is not received or received incompletely in near-range. This is the so-called geometric factor influence. So the backscatter lidar is not suit to the near-range measurement. Side-scatter lidar which is based on CCD detector is a developing tool for detection of atmospheric aerosol. The CCD camera is set to record the side-scattering light of laser beam [4]. The transmitting device and the receiving device are arranged in two places, and have no geometric factor. The vertical altitude resolution of side-scatter lidar is variable by adjusting the distance between laser beam and CCD detector, and has a good vertical altitude resolution in near-range generally. So side-scatter lidar is especially suitable to measure aerosol in near-range [5-6]. In this paper, backscatter lidar and side-scatter lidar are united in a joint to retrieve aerosol phase function, backscattering coefficient and aerosol extinction coefficient. Experimental System Experimental system contains backscatter lidar and side-scatter lidar. Backscatter and side-scatter lidars are united in a joint. The diagram of experimental system is shown in Fig. 1. Backscatter lidar consists of telescope,transient recorder, PMT and laser on the left. Side-scatter lidar system includes laser, CCD camera and geometric calibration on the right. The process of the experimental system can be described as a laser beam emitting into atmosphere,

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