Aiming at the detection of water vapor mixing ratio, particle linear depolarization ratio, extinction coefficient and cloud information, the Water vapor, Cloud and Aerosol Lidar (WVCAL) was developed by the lidar group at Ocean University of China. The Lidar consists of transmitting subsystem, receiving subsystem, data acquisition and controlling subsystem and auxiliary subsystem. These parts were presented and described in this paper. For the measurement of various physical properties, three channels including Raman channel, polarization channel and infrared channel are integrated in this Lidar system. In this paper, the integration and working principle of these channels is introduced in details. Finally, a measurement example which was operated in coastal area-Qingdao, Shandong province, during 2014 is provided.
In this study, a 1550 nm coherent high-spectral-resolution lidar (CHSRL) is developed to measure the optical properties of aerosols and atmospheric wind profiles in the atmospheric boundary layer. To determine the optical properties, a coherent frequency discriminator based on the fast Fourier transform is designed in the CHSRL to separate the Mie and the Rayleigh–Brillouin backscatter spectra to fulfill the needs of high-spectral measurements. The atmospheric wind velocity is retrieved using the simultaneously measured Doppler shift. This non-optical frequency discriminator is a feasible and low-cost solution compared to a narrow-bandwidth optical filter, such as a Fabry–Perot interferometer or an atomic filter. However, shot, amplifier spontaneous emission, and detector noise interfere with the Rayleigh–Brillouin spectrum. Therefore, a spectrum correction algorithm is proposed to recover the interfered Rayleigh–Brillouin spectrum, and the measurement results of the spectral line agree well with those modeled with Tenti S6 at different central frequencies. Finally, field observations for comparison are conducted with the co-located CHSRL, Raman lidar, and coherent Doppler wind lidar. The comparison results indicate that the correlation coefficient of the aerosol backscatter coefficient is 0.84. The correlation coefficient and standard deviation of wind velocity are 0.98 and 0.13 m · s−1, respectively.
Vertical profiles of the linear particle depolarization ratio p δ of cloud and aerosol in the Tibet Plateau were measured during the Tibetan Plateau atmospheric expedition experiment campaign with water vapor, cloud and aerosol lidar system, which is capable of depolarization ratio measurement. The atmospheric comprehensive observations were performed during July of 2013 at Litang (30.03°N,100.28°E), which is 3949 meters above the mean sea level, Sichuan province, China. It was the first time to detect and obtain the Tibetan Plateau cloud and aerosol lidar depolarization profiles to our knowledge. After completing the plateau experiment campaign, the lidar system measured the atmosphere above coastal area in Qingdao (36.165°N,120.4956°E). In this year, we continued to participate in the plateau experiment campaign in Nagchu (31.5°N,92.05°E), which is 4600 meters above the mean sea level, The Tibet Autonomous Region from 1 st ,July to 1 st ,September. Since particle size, shape and refractive index have an impact on linear particle depolarization ratio, one can classify the aerosol types and cloud phase in turn in the Tibetan Plateau and Qingdao area using linear particle depolarization ratio data. Generally, two calibration methods were applied: comparison of the lidar measurement data and CALIPSO simultaneous data method and half-wave plate ±45°switch method. In this paper we applied the comparison calibration method. The correlation coefficient between lidar measurement data and CALIPSO data reaches up to 84.92%, which shows great linear relation. Finally, after the calculation and calibration of the linear particle depolarization ratio measured during the plateau experiment campaign and observation in coastal area, the ice-water mixed cloud (0.15< p δ <0.5), water cloud ( p δ <0.15) and dusty mix(0.2< p δ <0.35) in Tibetan Plateau were occurred and classified. Meanwhile, the cirrus clouds ( p δ <0.5), water cloud, smoke and urban pollution (0.05< p δ <0.2) and dusty mix in Qingdao area were also occurred and classified.
Incoherent Doppler wind lidar measures the wind by detecting the frequency shift of the laser backscattering from aerosol and atmosphere molecules. The wind measurement sensitivity of edge detection technology like iodine vapor filter depends on the aerosol load of probe volume. The current Direct detect wind lidar system has to obtain the measurement sensitivity from the independent measurement or prior atmosphere aerosol data before accurate wind retrieval. Otherwise, the variation of aerosol mixing ratio would introduce great uncertainty in the wind speed measurement, which is unacceptable on airborne and space-borne Doppler lidar. This paper proposes a new method to achieve real-time wind speed calibration by three adjacent frequency laser pulses alternately transmitted. Three laser pulses are frequency locked to the middle and two wings of the iodine filter absorption line. Because the frequency of triple pulses is changing rather fast, it can be approximately regarded as a synchronous measurement of both aerosol mixing ratio and wind speed. By this way, we can not only ensure the wind measure accuracy, but also achieve the reliable wind field measurement on a mobile platform.
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