A detection of atmospheric relative humidity profile by UV Raman lidar

A new spectroscopic filter constructed with a high-spectral-resolution grating and two narrow-band mirrors is designed to separate the elastic scattering and the vibrational Raman scattering spectra in an ultraviolet (UV) Raman lidar system. The density of humidity and water vapor mixing ratio are calculated from the vibrational Raman scattering signals of N₂ and H₂O. Water vapor mixing ratio is retrieved from this development. With this measured water vapor mixing ratio, the relative humidity is calculated with atmospheric temperature profile obtained by another Raman temperature lidar. Preliminary experiments and comparison results between lidar and radiosonde showed that the UV Raman lidar system has the capability for profiling the water vapor mixing ratio up to a height of 2 km with less than 10% of the uncertainty under the conditions of laser energy of 300 mJ and signal-averaging time of 10 min.     

Transmittance ratio constrained retrieval technique for lidar cirrus measurements

This letter describes a lidar retrieval technique that uses the transmittance ratio as a constraint to determine an average lidar ratio as well as extinction and backscatter coefficients of transparent cirrus clouds. The cloud transmittance ratio is directly obtained from two adjacent elastic lidar backscatter signals. The technique can be applied to cirrus measurements where neither the molecular scattering dominant signals above and below the cloud layer are found nor cloudfree reference profiles are available. The technique has been tested with simulated lidar signals and applied to backscatter lidar measurements at Hampton University, Hampton, Virginia.     

Simultaneous measurement of atmospheric temperature,humidity, and aerosol extinction and backscatter coefficients by a combined vibrational–pure-rotational Raman lidar

Implementation of the pure-rotational Raman (PRR) lidar method for simultaneous measurement of atmospheric temperature, humidity, and aerosol extinction and backscatter coefficients is reported. The isolation of two wavelength domains of the PRR spectrum and the suppression of the elastically scattered light is carried out by a double-grating polychromator. Experiments involving elastic backscatter from dense clouds and a solid target confirm the high level of suppression of the elastic light in the corresponding acquisition channels of the two selected PRR domains. Calibration of the temperature channel was done both by comparison with an experimentally verified atmospheric temperature model profile and by inter-comparison with radiosondes. Night-time temperature profiles with high vertical resolution were obtained up to the lower stratosphere. The PRR temperature profile combined with the water vapor mixing ratio obtained from the ro-vibrational Raman channel is used to estimate the relative humidity. PACS 42.68.Wt; 42.68.Mj; 33.20.Fb     

Measurements for profiles of aerosol extinction coefficient,backscatter coefficient,and lidar ratio over Wuhan in China with Raman/Mie lidar

<正>The profiles of aerosol extinction,backscatter coefficient,and lidar ratio in the lower troposphere over Wuhan are measured by a multi-channel Raman/Mie lidar.Using the lidar ratio retrieved by Raman scattering principle,the profiles of aerosol extinction and backscatter coefficients are also retrieved by Mie scattering signals,without a prior assumption about their relation in the traditional pure Mie signals data analyses.The observations by both Raman and Mie are in good agreement with each other.The high coherence shows that the system is reliable,and the Mie and Raman channels are in good adjustment and have the same field of view.     

Study of atmospheric water in gaseous and. liquid state by using combined elastic–Raman. depolarization lidar

A combined elastic–Raman lidar system based on a tripled Nd:YAG laser is used for the separate detection of elastic backscatter and Raman signals from atmospheric nitrogen, water vapor and liquid water and for their depolarization measurement. Vertical profiles of water-vapor and liquid-water content measured under clear-sky conditions behave differently: inside the boundary layer the ratio of liquid-water to water-vapor Raman backscatters rises with altitude. The depolarization measurements bring additional information about atmospheric scattering. The observed depolarization ratio of the water-vapor Raman signal is about 14%, while for liquid water this ratio varies in the 30–75% range, which exceeds the depolarization of bulk water and is attributed to the water-aerosol effects. Raman contours of water vapor and liquid water are partially overlapped, and bleed-through of liquid-water Raman backscatter leads to enhancement of depolarization of the water-vapor Raman signal. This parameter may be used as a convenient indicator of liquid-water interference in water-vapor measurements. Received: 12 December 2000 / Revised version: 27 September 2001 / Published online: 7 November 2001     

合肥上空大气二氧化碳Raman激光雷达探测研究

Raman激光雷达是用于大气成分探测与特性研究的有效工具.介绍了中科院安徽光学精密机械研究所自行研制的一台用于测量低对流层大气CO₂时空分布的Raman激光雷达系统,并进行了一系列观测实验和对比分析.系统选用波长355 nm的紫外激光作为光源,利用光子计数卡双通道采集大气中N₂和CO₂的Raman后向散射信号与Li-7500型H₂O/CO₂分析仪进行对比标定,通过反演获得了大气CO₂水平与垂直方向时空分布廓线,并且获得了合肥地区大气边界层CO₂的夜变化趋势.结果表明,大气CO₂在空间的分布相对均匀,Raman激光雷达与CO₂分析仪变化趋势一致性较好,能够对大气CO₂时空分布进行有效、连续的观测.     

Two-wavelength lidar inversion algorithm for determination of aerosol extinction-to-backscatter ratio and its application to CALIPSO lidar measurements

A modified two-wavelength lidar inversion algorithm is proposed to aid in the retrieval of aerosol extinction-to-backscatter ratios (lidar ratio) as well as backscatter coefficients and extinction color ratios from simultaneous two-wavelength elastic backscatter lidar measurements. To demonstrate the feasibility of the algorithm, both the Raman method and the two-wavelength method have been applied to the ground-based measurements at 355 and 532 nm; moreover, it has been applied to the data acquired by the Cloud Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) lidar, and to the simultaneous ground-based lidar measurements carried out at Napoli (southern Italy, 40.838 °N, 14.183 °E, 118 m above sea level). Three cases of Saharan dust transport towards Europe have been considered. From the comparison, it can be found that the values of lidar ratio and backscatter coefficient retrieved by the modified two-wavelength algorithm are in good agreement with those obtained by the Raman method. Moreover the retrieved mean values of the lidar ratios and color ratios are in agreement with those reported by other authors.     

Analysis of influence of atmosphere extinction to Raman lidar monitoring CO2 concentration profile

Lidar （Light detection and ranging） system monitoring of the atmosphere is a novel and powerful technique tool. The Raman lidar is well established today as a leading research tool in the study of numerous important areas in the atmospheric sciences. In this paper, the principle of Raman lidar technique measurement CO2 concentration profile is presented and the errors caused by molecular and aerosol extinction for CO2 concentration profile measurement with Raman lidar are also presented. The standard atmosphere extinction profile and ＇real-time＇ Hefei area extinction profile are used to conduct correction and the corresponding results are yielded. Simulation results with standard atmosphere mode correction indicate that the errors caused by molecule and aerosol extinction should be counted for the reason that they could reach about 8 ppm and 5 ppm respectively. The relative error caused by Hefei area extinction correction could reach about 6%. The errors caused by the two components extinction influence could produce significant changes for CO2 concentration profile and need to be counted in data processing which could improve the measurement accuracies.     

Measurement of tropospheric CO2 and aerosol extinction profiles with Raman lidar

A prototype Raman lidar was designed for monitoring tropospheric CO2 profile and other scientific investigatious.The third harmonic of Nd:YAG laser (354.7-nm wavelength) was used as stimulated light source to provide nighttime measurements.Filter with high rejection ratio performance was used to extract CO2 Raman signals from Rayleigh-Mie scattering signals effectively.To improve the real time monitoring function,a two-channel signal collection system was designed to collect CO2 and N2 Raman scattering signals simultaneously. The N2 Raman scattering signals were used to retrieve aerosol extinction coefficient.Typical features of CO2 concentration profile and aerosol extinction coefficient in Herei were presented.The mixing ratio of atmospheric CO2 in Hefei can reach about 360-400 ppmv.     

水汽探测拉曼激光雷达的新型光谱分光系统设计与分析

提出并设计了一套新型的大气水汽和气溶胶探测用紫外域拉曼激光雷达系统, 以二向色镜和超窄带滤光片构成高效率拉曼光谱分光系统, 实现激光雷达大气回波信号中米-瑞利散射信号、 氮气和水汽的振动拉曼散射信号的精细分离和高效率提取. 利用美国标准大气的分子散射模型和实测的大气米散射信号模型, 对分光系统的米-瑞利散射信号的抑制率、大气水汽测量的信噪比和误差进行数值仿真设计. 搭建实验系统对西安地区夜间的大气水汽进行实验观测, 并利用有云天气下实测的激光雷达回波信号, 反演获得大气后向散射比和水汽混合比的相关特性, 验证了该拉曼光谱分光系统对米-瑞利信号的抑制率达到10^-7以上量级. 理论和实验结果表明, 设计的新型拉曼光谱分光系统可以在大气后向散射比为17时, 实现水汽探测误差小于15%, 满足拉曼激光雷达系统对大气水汽的高效率探测. 关键词： 拉曼激光雷达 水汽混合比 大气后向散射比     

Ultraviolet Raman lidar for high-accuracy profiling of aerosol extinction coefficient

An ultraviolet （UV） Raman lidar system at 354.7 nm has been developed for accurately measuring the aerosol extinction profiles. A spectroscopic filter combining a high-spectral-resolution grating with two narrowband mirrors is used to separate the vibrational Raman scattering signal of N2 at a central wavelength of 386.7 nm and the elastic scattering signal at 354.7 nm. The aerosol extinction is derived from the Raman scattering of N2 and the elastic scattering by the use of Raman method and Klett method, respectively. The derived results of aerosol extinction are used to compare the difference of two retrieval methods, and the preliminary experiment shows that the Raman lidar system operated in analog detection mode has the capability of measuring aerosol profiles up to a height of 3 km with a laser energy of 250 mJ and an integration time of 8 min.     

基于三级Fabry-Perot标准具的纯转动拉曼测温激光雷达

提出了新的纯转动拉曼测温雷达系统,即以种子激光注入锁定的Nd:YAG激光器为激发光源,采用基于三级Fabry-Perot(F-P)标准具的双通道分光结构代替双光栅单色仪结构.通过通道中宽带滤光片(带宽为7nm)及F-P标准具的组合使用,对532nm激发光的大气Mie-Rayleigh弹性回波散射抑制比可达10^-10,对量子数J=±6,J=±12的N₂纯转动拉曼散射光谱线接收带宽均小于10pm,因此能充分抑制大气背景辐射噪声及O₂纯转动拉曼谱线的干扰,从而实现了单谱线比反演温度,提高了探测精度,且可在白昼探测大气对流层温度.最后通过探空气球测得的对流层温度垂直分布逆向模拟了该系统双通道的Raman信号曲线,证实了该系统的可行性. 关键词： 拉曼激光雷达 纯转动拉曼散射 三级Fabry-Perot标准具 对流层     

Multi-scalar measurements in a premixed swirl burner using 1D Raman/Rayleigh scattering

Instantaneous measurements of temperature, equivalence ratio, and major species were performed along a one-dimensional probe volume using simultaneous Raman/Rayleigh scattering in an unconfined turbulent lean-premixed swirling methane/air flame. Temperature was determined from Rayleigh scattering and the major species, CO₂, O₂, N₂, CH₄, H₂O, and H₂ from Raman scattering. Effective Rayleigh cross-sections were corrected using the local chemical composition obtained from Raman scattering. These experiments were conducted to investigate the compositional structure of a lean-premixed swirling flame in detail and to complement previous measurements of the underlying flow field. The flame was classified within a revised regime diagram at the cross-over between corrugated flames and thin reaction zones. Instantaneous temperature profiles varied significantly showing shapes ranging from laminar-like flamelets to mixing between reacted fluid elements and secondary air. Different thermo-kinetic states could be assigned to the inner and outer recirculation zones and to the inner and outer mixing layers. Linked to published velocity data of this flame, the present multi-scalar data are useful for validation of numerical simulations.     

LIDAR investigation of properties of atmospheric aerosol

In the paper application of lidars for investigation of aerosol particle size distribution and for observation of aerosol consisting of solid state particles is presented. For size distribution the multiwavelength lidar and original method of data analysis was applied. For registration of dust transported to Central Europe from Sahara and Middle East deserts analysis of depolarization of the backscattered signals was used. In order to solve the lidar equation measurements of total atmospheric optical depth by means of Microtops sun photometer was done. Mean size and the aspect ratio of dust particles were determined by comparing of lidar observations with data from T-matrix calculations.     

Direct measurement of the Rayleigh scattering cross section in various gases

Using the laser-based technique of cavity ring-down spectroscopy extinction measurements have been performed in various gases straightforwardly resulting in cross sections for Rayleigh scattering. For Ar and N₂ measurements are performed in the range 470-490 nm, while for CO₂ cross sections are determined in the wider range 470-570 nm. In addition to these gases also for N₂O, CH₄, CO, and SF₆ the scattering cross section is determined at 532 nm, a wavelength of importance for lidar applications and combustion laser diagnostics. In O₂ the cross section at 532 nm is found to depend on pressure due to collision-induced light absorption. The obtained cross sections validate the cross sections for Rayleigh scattering as derived from refractive indices and depolarization ratios through Rayleigh's theory at the few %-level, although somewhat larger discrepancies are found for CO, N₂O and CH₄.     

Determination of reference values for optical characteristics in multiwavelength optical detection and ranging (lidar) measurements of atmospheric extinction coefficients

We have studied multiple regressions between the spectral aerosol extinction coefficient ε, backscatter indicatrix g_π, and light-scattering coefficients β_θ at angles of θ = 1–180°, which we used to select the optimal scattering angle for determining the extinction coefficient at the wavelengths 0.350, 0.532, and 1.060 μm. We have estimated the errors in determination of the values of ε and g_π at the given wavelengths for different atmospheric situations with different meteorological parameters. We have shown that it is possible to use the spectral β_θ values at a 33° angle to determine the reference values for ε(λ) and g_π(λ) at λ = 0.350, 0.532, and 1.060 μm in laser detection and ranging (lidar) measurements, and we give examples of recovering the vertical profiles of ε in a slightly turbid atmosphere from the results of simultaneous multiwavelength lidar and nephelometric measurements. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 6, pp. 767–772, November–December, 2007.     

探测大气中CO2的Raman激光雷达

基于大气激光后向散射光谱，研究和设计了探测大气CO₂浓度的Raman激光雷达,其发射机采用Nd∶YAG激光的三倍频354.7nm作为工作波长,发射的单脉冲能量350mJ,重复频率20Hz；接收机采用了光电倍增管(量子效率25%)和光子计数器(计数速率200MHz),探测CO₂的Raman散射371.66nm(频移1285cm^-1)信号,(1小时累加)近地面2.5km以内信噪比不小于8.采用组合滤光片来抑制强的354.7nm Mie-Rayleigh后向散射和氧气375.4nm Raman后向散射对信号的严重干扰. 比较分别来自大气CO₂和参考气体N₂的Raman后向散射回波,可反演出大气中CO₂的相对浓度. 关键词： 大气光学 激光雷达 Raman散射光谱 参考气体 Mie-Rayleigh散射     

Development of a SNR parameterization scheme for general lidar assessment

We present a general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets. By introducing a well-defined atmospheric reference medium and by individually examining and decomposing the contributions of lidar system parameters including lidar transmitter power, field of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise ratio, we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration, and so on.This revised version was published online in August 2005 with a corrected cover date.     

Raman Lidar Measurements of Aerosol and Cloud Optical Properties in the Troposphere

A Raman lidar has been developed with photon counting technique. Aerosol and cloud extinction coefficients are derived by nitrogen (N2) molecular Raman scatter returns in the troposphere. Both backscatter coefficients and extinction-backscatter-ratios of aerosol and cloud are presented by simultaneously combining N2 Raman and Mie-Rayleigh returns of aerosol and molecule. Ratios of extinction to backscatter between 20 sr and 70 sr are usually found for aerosol, but less than 15 sr for mid-high altitude cloud in the troposphere.