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.
KEYWORDS: Aerosols, Mass attenuation coefficient, LIDAR, Atmospheric particles, Solar radiation, Humidity, Troposphere, Clouds, Information operations, Signal attenuation
A Mie lidar was used to make observation of Asian dust over Hefei (31.90° N, 117.16° E) in the every spring from 1998 through 2004. This paper presents main features of vertical distribution and temporal variation of Asian dust extinction coefficient at 532 nm wavelength during the seven years.
There were two kinds of vertical distributions of Asian dust extinction coefficients. One indicated that the Asian dust particles intruded into the local boundary layer, causing the very thick dust layer with depth of about 3-4 km. The other showed that the Asian dust passed over Hefei area just above the boundary layer. The aerosol extinction coefficients in the elevated dust layer within the middle troposphere from 3 to 6 km were unusual large.
Seasonal average aerosol extinction coefficient profiles showed that larger aerosol extinction coefficients from 1 km to 10 km altitude range were observed in the springtime rather than in any other season.
We conduct network observations using ground-based Mie-scattering lidars in Asian region in cooperation with various research organizations and Universities. Primary purpose of the network is for studying generation and transport of Asian dust, observing air pollution and biomass burning aerosols for atmospheric environment studies, observing aerosol vertical distribution and temporal variation for atmospheric radiation studies and climatology, and for validation of chemical transport models and satellite remote sensors. At present, lidars are operated continuously at twelve locations in Japan, China, Korea, and Thailand. The lidars used in the network are two-wavelength (532 nm and 1064 nm) Mie-scattering lidars having depolarization measurement function at 532nm. Flashlamp-pumped compact Nd:YAG lasers are used as the light source. We developed a method for estimating the extinction coefficient of non-spherical air-pollution aerosols separately using the depolarization ratio. This method is based on a simple assumption that observed aerosols are external mixture of two types of aerosols, but it is practically very useful especially for inter-comparison with chemical transport models. We also studied a method for characterizing aerosols using the depolarization ratio and the wavelength dependence of the backscatter coefficient. Asian dust phenomena were observed with the network since spring of 2001. The frequency of the occurrence of dust events and the vertical distribution characteristics were analyzed. Also, seasonal and year-to-year variations were analyzed. At the same time, transport of dust and air-pollution aerosols were studied by comparing the temporal variation of lidar profiles with chemical transport model results.
As one of the most versatile tools lidar plays an important role in the field of the atmospheric and environmental probing for its special properties of fine resolution continual operation long-range and wide scanning. The most important parameter of lidar is the signal-to-noise ratio (SNR) and it not only shows the ability in remote sensing but also gives some instructions in designing of lidar. But there is still not a suitable and scientific way to calculate the lidar's signal-to-noise ratio in practice. Under this circumstance the new and reasonable method is present from the experience in lidar working and its data processing and the analyses of main influencing factors are also made on real lidar data.
The 1064nm Doppler wind lidar with a dual Fabry-Perot etalon based on the edge technique has been developed to measure wind profile in the troposphere. The construction of the lidar system is described in the paper. The dual etalon with high-spectral resolution are used to discriminate the Doppler shift from the aerosol backscattering. The accuracy of the lidar system is analyzed and discussed especially for the etalon parameters. The transmittance curve of the etalon is measured and the results show that the standard deviation of the transmittance will cause the velocity error of 0.5m/s. The lidar system is estimated to measure the wind speed up to 10km with the accuracy of less than 2m/s. The preliminary result of the radial velocity measurements has been obtained.
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).
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.
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.
The violent eruption of Philippine volcano Pinatubo in mid June of 1991 caused a serious perturbation on the stratospheric aerosols for a long period. In the paper, we report L625 lidar observational results in the period of 1991 - 1996, including evolution of volcano Pinatubo cloud. The time variation and vertical distribution of the volcanic cloud height, thickness, peak-scattering ratio, and integrated backscattering coefficients will be analyzed. L625 lidar measurement data of stratospheric aerosol reveal the characteristics of background period before the volcanic eruption, the evolution of the Pinatubo volcanic cloud, and present new background level.
In this paper, the solution to lidar equation for tropospheric aerosol monitoring is introduced. System structures and characteristics for L300 lidar are presented. Observation method and data processing procedure are described. Optical properties of tropospheric aerosols determined by the lidar measurements over Hefei are analyzed and discussed.
This paper systematically discussed the three-wavelength dual differential absorption lidar (dual-DIAL) method for measuring the stratospheric and tropospheric ozone profiles in the presence of high loading or inhomogeneous aerosols along the measurement path. Results of theoretical analysis and comparisons with DIAL and aerosol correction method show that the three-wavelength dual-DIAL method not only can greatly reduce the effect of aerosols on tropospheric and stratospheric ozone measurements, but also can get more accurate ozone profiles than DIAL after aerosol correction. The system error of three-wavelength dual-DIAL due to aerosols is kept in a low level. As the system error in the three-wavelength dual-DIAL is almost insensitive to the spatial inhomogeneity of aerosol loading and aerosol optical properties, this method does not need to known the detailed information about the spatial distribution of aerosol loading and aerosol optical properties. In the regions contained high loading or inhomogeneous aerosols, accurate ozone profile can be obtained directly from the lidar return signals with three wavelengths dual-DIAL method. Experimental results indicate the three wavelengths dual- DIAL method is effective.
A new sun-photometer intended to perform accurate measurements of the spectral characteristics of both direct solar and aureole radiation is presented. Controlled by a microcomputer, the photometer carries out the following functions: active tracking of the sun's center, transforming optical filters, adjusting the gain of an amplifier, sampling and storing the data on time.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.