Differential absorption lidar (DIAL) is an effective instrument for detecting nitrogen dioxide (NO2) in the atmosphere. Under the condition of heavily polluted weather, aerosol has a serious influence on the concentration inversion of NO2. In this paper, using both echoes of SO2 and NO2 at weak absorption wavelengths (301.50 nm and 446.60 nm) in differential absorption lidar, the aerosol extinction coefficient and backscattering coefficient are calculated by recursive inversion algorithm. It is also used to correction the concentration distribution of NO2 on the detective path. The experimental results show that the standard deviation of NO2 concentration distribution using the correction algorithm is less than 10μg/m3 , and the fluctuation range is less than that of direct inversion. This concentration inversion algorithm overcomes the uncertainty caused by the assumption of the boundary value at the reference point when using the single-wavelength Klett or Fernald backward integration method to invert the aerosol extinction coefficient in heavily polluted weather, and has higher accuracy.
Based on the carbon dioxide mass mixing ratio concentration profiles of Hefei Science Island from 2013 to 2016, the distribution characteristics of carbon dioxide in the subtropical monsoon climate and the characteristics of carbon dioxide source and sink in Hefei Science Island were analyzed from the night, season and year respectively. At lower altitudes, CO2 builds up during nighttime hours as respiration is trapped within the nocturnal boundary layer. Throughout this nighttime the CO2 concentration at 390m shows that only little variation. After sunrise, convection begins to spread the CO2 trapped at low levels to higher altitudes. When the measurement height was more than 100m, the obvious seasonal change was shown, with the minimum in summer and the maximum in winter, which the difference in concentration of about 19.32mg/m3 . The annual distribution of the concentration of carbon dioxide from 2013 to 2016 had no significant difference in the gradient change of the height above 100m, the correlation coefficient was above 0.9, and the CO2 vertical concentration goes up with a rate of about 4.35mg/m3 per year. Through data analysis from three different timescales, it could be concluded that the concentration of carbon dioxide near the ground was greatly influenced by the atmospheric environment. The seasonal distribution of carbon dioxide concentration was the result of a combination of atmospheric movement and the activities of plants and animals. In the process of long-term carbon dioxide cycling, there was a current that the near-surface carbon dioxide transported to a higher altitude.
In order to initially explore the different temporal and spatial distribution characteristics of sulfur dioxide (SO2) and nitrogen dioxide (NO2) concentrations in Huainan, the gas concentration detections were carried out at Huainan Academy of Atmospheric Sciences by the differential absorption laser radar system of Anhui Institute of Optics and Fine Mechanics. According to the detected distribution profiles of atmospheric SO2 and NO2 concentrations in part of the months from July 2016 to June 2017, in this paper, the typical examples are selected to analyze the distribution characteristics of SO2 and NO2 from three aspects: diurnal variations of horizontal concentration, vertical concentration changes and monthly variations of horizontal concentration. According to the SO2 and NO2 concentration distribution profiles in the selected examples, the following conclusions can be drawn:(1) The concentrations of SO2 and NO2 at night are greater than that of SO2 and NO2 in the afternoon on the same day;(2) The vertical concentrations of SO2 and NO2 decrease with the increasing height;(3) The monthly variations of SO2 and NO2 horizontal concentration are the highest in the winter months, and the lowest in the summer months, followed by the spring and autumn months. The changes in SO2 and NO2 concentrations are the result of a combination of population activities and changes in meteorological conditions.
The aerosols near the ground are closely related to human health and climate change, the study on which has important significance. As we all know, the aerosol is inhomogeneous at different altitudes, of which the phase function is also different. In order to simplify the retrieval algorithm, it is usually assumed that the aerosol is uniform at different altitudes, which will bring measurement error. In this work, an experimental approach is demonstrated to measure the scattering phase function of atmospheric aerosol particles at different heights by CCD lidar system, which could solve the problem of the traditional CCD lidar system in assumption of phase function. The phase functions obtained by the new experimental approach are used to retrieve the aerosol extinction coefficient profiles. By comparison of the aerosol extinction coefficient retrieved by Mie-scattering aerosol lidar and CCD lidar at night, the reliability of new experimental approach is verified.
Using SolidWorks software, the finite element modal analysis of a vehicle-borne pollution monitoring lidar cabin is carried out. The lidar cabin for the integrated lidar can ensure that the lidar system has good maneuverability and can effectively monitor the emission of air pollution. Since lidar is an integrated system of optics, mechanism, electricity and calculation, the performance of the cabin is directly related to the safety of the equipment and the lidar to work properly. Firstly, the cubic structure is modeled to simulate the cubic structure. Then, the model of the cabin model is analyzed by using the simulation plug-in, and the first 10 modes and natural frequencies are analyzed and recorded. The calculation results show that the cabin is dominated by bending vibration, and the amplitude area is concentrated in the opening of some windows and doors on each board. Therefore, we should increase the number of reinforcement bars or the strength of the skeleton in the vicinity of the door and window. At the same time, to avoid the resonance and ensure the precision of the optical elements and the electrical components and avoid structural damage of the cabin, the incentive frequency should be keep away from the natural frequency of the cabin. The vehicle-borne lidar system has been put into operation, and the analysis results have direct meaning to the transport of the cabin and the normal work.
Lidar instruments are efficient detectors of air pollutants such as nitrogen dioxide (NO2). However, the measurement errors are not negligible due to the influence of the aerosol in the atmosphere. We present a novel lidar for measuring tropospheric NO2 vertical profiles. For improving the received powers, the emitter unit consists of two pulsed pump laser – dye laser combination, and use three wavelengths of 448.10nm, 447.20nm and 446.60 nm corresponding to the strong, medium and weak absorption of NO2 respectively. The effects of aerosol on tropospheric NO2 measurements by three - wavelength (448.10 -447.20 -446.60 nm) dual differential absorption lidar (dual-DIAL) and conventional two - wave length (448.10- 446.60nm) differential absorption lidar (DIAL) are theoretical analyzed, and their system err are computer simulated. Experimental results show that the three - wavelength dual - DIAL method is more effective to reduce the effects of aerosol than the two - wavelength DIAL method, and its system error is no more than 4% without correcting the aerosol effect.
The differential absorption lidar (DIAL) is a powerful and convenient tool for detecting the atmospheric trace gases. Based on dual wavelength differential absorption principle, we develop a set of lidar for measuring the concentration and distribution of the atmospheric SO2. This paper introduces the software, hardware and specific parameters of each subsystem in detail, then horizontal and vertical azimuth detection results are given. This lidar system adopts two tunable narrow linewidth dye lasers which pumped by Nd:YAG lasers, and produces l 600.10nm laser and 603.00nm lasers alternately. The lasers are frequency doubled by two second-harmonic crystals respectively and marked as λon=300.05nm and λoff=301.50nm which corresponds the strong absorption wavelength and the weak absorption wavelength of SO2 absorption spectrum. They are merged into one beam, and then expanded twelve times, and transmitted into the atmosphere coaxially with telescope finally. The back scattering signals are received by telescope system and converted into electrical signals by photomultiplier tube (PMT) after being collimated and filtered. These electrical signals are obtained by A/D acquisition card and stored in the computer for retrieving the concentration and distribution of the atmospheric SO2. Some field experiments are conducted in Huainan Atmospheric Science Research Institute, and we get some satisfactory results. On June 28th, 2016, the mean concentration of atmospheric SO2 is about 3.7 ppb in the range from 0.8km to 3.0km in horizontal azimuth. It conforms with the result of ground instrument from meteorological department. The vertical orientation detection is also performed at night of June 28th, 2016, and the atmospheric SO2 fluctuates in 0-5ppb which mainly exists below 1.5km.
Cirrus cloud has an important effect on the radiation balance between the earth’s surface and the atmosphere. The vertical structures, optical depth and effective lidar ratio of cirrus cloud detected by Mie scattering-polarization-Raman lidar system in Beijing from April 11 to December 31, 2012 are analyzed. The results show that the cloud height in Beijing is lower in spring and higher in autumn, with a mean value of about 8km. The mean of cloud thickness is 0.74km. The mean of optical depth is 0.092, and most observed cirrus cloud is thin while optical depth is less than 0.3. The effective lidar ratio of cirrus is lower in summer and higher in winter, inversely related to local temperature, with a mean value of 32.29Sr.
The atmospheric temperature is an important meteorological parameter. The rotational Raman lidar temperature measurement system is usually used for retrieval of atmospheric temperature according to the echo signal intensity ratio. UV double grating monochromator (DGM) is a kind of spectroscopical equipment for extracting the rotational Raman's spectra. The UV DGM consists of optical fibers , focal plates , lenses and gratings. Correct parameters of the gratings, lenses, fibers are essential to the successful development of DGM. First, a suitable grating is selected according to the grating diffraction theory. Second, the diameter and focal length of lens are chosen according to ruled area and blaze angle of grating, the numerical aperture of fiber and how difficult machining is . Finally, the range of fiber core diameter is chosen according to the distance between the sixth and the twelfth spectral line on the focal plane. In order to compare the different fiber core diameter's statistical temperature error, and suppression ratio of elastic scattering light, some numerical calculations are conducted. The simulation results show that the measurement accuracy increases in the evening and approximately decreases during daytime with the increase of input fiber core diameter .As the input fiber core diameter increases, the rejection ratio is decreasing ,but they are all more than 7 orders of magnitude. It is preferable to choose input fiber with core diameter of 300um during the daytime and 600um at night. The correct parameters of grating, lens and fiber provide theoretical basis for the development of the UV DGM.
Three microphysical backscatter ratios (color ratio, depolarization ratio, and lidar ratio) widely used for interpretation of lidar signals returned from cirrus clouds have been calculated for the first time. The physical-optics code developed earlier by the authors is applied. Though the data are obtained for the hexagonal ice plates and columns, that are the simplest crystal shapes, their arbitrary spatial orientation has been taken into account. The lidar experimental data measuring simultaneously the depolarization ratio and color ratio in cirrus clouds are also presented.
The fourth harmonic (266nm) of a pulsed Nd: YAG laser is used to pump Raman cells filled with D2 and D2/He. The dependences of the energy conversion efficiency of stimulated Raman scattering radiations upon the system parameters such as the pump energy pressure of pure D2 and partial pressure of He in D2/He mixture were experimentally studied. The maximum energy conversion efficiency of the first Stokes radiation (S1, 289.O4nm) reaches 22.1% in D2/He. The conditions to improve the energy conversion efficiency of Si were found. The results have been used to optimize the laser transmitter system for a S02 differential absorption lidar (S02-DIAL).
ABSTRACT
This paper describes one Raman lidar system for measurements of optical parameters for tropospheric aerosol and cirrus at Hefei (31.9 N/117.17 E) station. Typical extinction and backscatter coefficients profiles of tropospheric aerosol and cloud are presented. Many observation cases show the positive relationship between aerosol optical parameters and water vapor distribution. Some aerosol distributions were captured for dust storm by this Raman lidar in the spring of year 2001~2002. Angstrom coefficient profiles of aerosol are derived in the free troposphere by combining two-wavelength Raman-elastic scattering channels, those values indicate smaller for dust aerosols. Optical thickness and scattering ratio profile of cirrus are obtained by this Raman lidar. The values of extinction to backscatter ratios are frequently found between 20 sr and 70 sr for free tropospheric aerosol, but less than 20 sr for cirrus clouds.
In this paper L625 UV-DIAL system was described, and ozone measurement method was briefly introduced. Some observation results were presented and discussed. Ozone data were obtained by L625 UV-DIAL system at Hefei for more than two hundred days. The characteristics of ozone vertical profiles are analyzed, its seasonal variation and stratosphere-troposphere exchange process. Two yearly averaged profiles and their standard deviations were presented.
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