Liquid water content (LWC) and cloud droplet effective size (CDES) are important factors affecting atmospheric radiative transfer, and measurement of these parameters in clouds is essential. For homogeneous liquid cloud (constant extinction coefficient) with a gamma size distribution of cloud droplets, we find that LWC and CDES can be retrieved from two parameters obtained from a multiple-field-of-view (MFOV) Lidar: the intercept of the range-corrected Lidar signal (IRCLS) and the slope of the range-corrected Lidar signal (SRCLS) at different sizes of FOV. Monte Carlo simulations reveal that IRCLS at different sizes of FOV varies with both extinction coefficient and CDES while SRCLS varies only with the extinction coefficient, which depends on both LWC and CDES. This means that, after extracting the extinction coefficient using SRCLS, we can easily obtain CDES from IRCLS, and LWC can then be determined using the extinction coefficient. An innovative MFOV Lidar system is constructed to measure the LWC and CDES. A series of experiments is conducted in the northern suburb of Nanjing, China, and the LWC and CDES of homogeneous liquid cloud are obtained. Comparisons among results from the MFOV Lidar, theoretical calculation, and the global precipitation measurement satellite verify our proposed method.
An all‐fiber pulsed coherent Doppler LIDAR (CDL) system is described. It uses a fiber laser as a light source at a 1.54‐μm wavelength, producing 200 μJ pulses at 10 kHz. The local oscillator signal is mixed with the backscattered light (of different frequency) in the fiber. The atmospheric wind speed is determined through the fast Fourier transform applied to the difference frequency signal acquired by an analog‐to‐digital converter card. This system was used to measure the atmospheric wind above the upper‐air meteorological observatory in Rongcheng (37.10°N, 122.25°E) of China between January 7 and 19, 2015. The CDL data are compared with sounding‐ and pilot‐balloon measurements to assess the CDL performance. The results show that the correlation coefficient of the different wind‐speed measurements is 0.93 and their discrepancy 0.64 m/s; the correlation coefficient for wind‐direction values is 0.92 and their discrepancy 5.8 deg. A time serial of the wind field, which benefits the understanding of atmospheric dynamics, is presented after the comparisons between data from CDL and balloons. The CDL system has a compact structure and demonstrates good stability, reliability, and a potential for application to wind‐field measurements in the atmospheric boundary layer.
Aerosol plays an important role in regularization of the earth’s energy balance. Compared with light detection and ranging (LIDAR) pointing vertically, scanning LIDAR is a useful tool for detection of the spatial and temporal distribution of aerosols. A scanning LIDAR is constructed in which a compact 532-nm laser is bound to the telescope. Under the command from the serial port, the LIDAR can observe in different scanning modes. We introduce the structure and key parameters of the scanning LIDAR, and then verify its measurement ability by comparison with the Rayleigh–Raman–Mie LIDAR. Observation of a plume emission from a chemical factory is conducted in the northern suburbs of Nanjing, China. In order to obtain the distribution of the plume emission, the slope method and Fernald method are combined to invert the extinction coefficient of the plume. Analysis of the data shows that the scanning LIDAR can be used to monitor the relative emission concentrations of pollutants and depict the process of the pollutants’ diffusion. The scanning LIDAR can also be used to measure the three-dimensional variation of the extinction coefficient by automatic volume scanning.
A Mie-Rayleigh-Raman lidar contains a 200mJ-532nm laser, a 400mm telescope and three detection channels was
constructed in this paper. The three detection channels are Mie channel, Rayleigh channel and Raman channel
respectively. For the intensity of the aerosol backscattering in boundary layers, analog PMT is used in the Mie channel,
from the signal of the analog PMT aerosol extinction can be obtained. The Rayleigh channel detects the Rayleigh
backscattering of the atmospheric molecular, while the Raman channel detects the vibrational Raman signal of N2, which
is 607nm in the system. From the Rayleigh and Raman channels above, air density profile and then the temperature
profile from 5Km to 55Km can be inverted. Primary measurement results were also presented in this paper, to verify the
accuracy of the temperature, comparison was conducted between the lidar measurement and the atmospheric model. The
result showed good agreements. Backscattering coefficient of aerosol in the range of 10Km was also presented in the end,
which indicated the ability of aerosol monitoring.
Mie theory of spherical particle is introduced in this paper. Using Mie theory, scattering energy
distribution of typical-size cloud droplet is presented, as well as the relative intensity collected in
certain solid angle of different size droplet. An airborne probe of cloud droplet is designed based
on the Mie theory. In this probe, a 685nm diode laser is used to illuminate the cloud droplets in the
sensitive volume. The scattering energy between 4°and 12°(solid angle) of forward scattering is
collected. From the energy of the forward scattering, the sizes of the cloud droplets can be
obtained. In the system, an aspheric lens system is used to provide uniform illumination with high
use efficiency of laser. Most of the key parameters of the receiving optics system are presented,
the designed deep of field (DOF) is 3mm. With this probe, the cloud droplet concentration of size
between 4-50um can be measured.
Fringe technique is preferred to edge technique of wind measurement in troposphere for a direct-detect Doppler wind lidar. However, most fringe-technique based Doppler lidar systems have been developed to date are based on conventional Fabry-perot interferometer. The purpose of this paper is to introduce our development of fringe-technique lidar based on Fizeau interferometer in which the signal can be detected more conveniently using commercial linear detector. The pre-development of the lidar system is described including interferometer's optimum design, the frequency stabilization of Fizeau interferometer and the choice of multi-anode detector. In additional, the wind error of the system is simulated with taking account of Rayleigh noise. Results shows that the wind error can be less than 0.56m/s under 5 km with 30s integral time.
Base on the theory of the thick grating, volume phase grating (VPG) is analyzed numerically in light of thick grating theory and the characteristics of VPG’s gain spectrum in connection with the variation of parameters are presented, based on which a novel dynamic gain equalizer (DGE) is designed. Simulation shows that the DGE designed can work well.