A lidar for measuring fluorescence from atmospheric aerosols was constructed with a third harmonic Nd:YAG laser, a 1-
m diameter telescope, and a 32-channel time-resolved photon counting spectrometer system. Fluorescence of aerosols in
the spectral range from 420 nm to 510 nm was studied with the excitation at 355 nm. The distribution of fluorescent
aerosols was studied in the time-height indications of the broad fluorescence. Type of the aerosols was identified from
simultaneous observation with a polarization lidar in the Asian dust and aerosol observation lidar network (AD-Net). It
was found that Asian dust and air-pollution aerosols transported from urban or industrial areas emit fluorescence.
Fluorescence efficiency was roughly estimated for these aerosols. The results suggest fluorescence measurements
combined with the measurement of microphysical parameters of aerosols using a multiple-wavelength Raman lidar or
high-spectral-resolution lidar will provide useful information for characterizing chemical properties of aerosols.
In inelastic Raman scattering the scattered signal consists of radiation that has undergone a frequency shift which is
characteristic for the stationary energy states of an irradiated molecule. Nowadays, Raman and fluorescence
spectroscopy is commonly used in chemistry. Information on the radiation that results from transition between the
vibrational energy states of the excited molecules, respectively, is specific to the chemical bonds and symmetry of
molecules. This radiation therefore provides unique information regarding the irradiated molecule according to which the
molecular species can be identified. Raman spectroscopy represents a particularly powerful tool for laser remote sensing
because it allows us to both identify and quantify the trace constituent relative to the major constituents of a mixture.
In this paper we present a multi-channel spectrometric lidar system which allows us to measure Raman and fluorescence
spectrums that give us information on chemical signatures characteristic for chemical components of aerosol particles
and pollutions. In the following, we describe the methodology, the system and we show experimental results.
This paper reports on the results of measurements of the aerosols and the clouds optical properties in the troposphere over Tsukuba, Japan (104.12°E, 36.05°N, 27 above sea level). We carried out the experiments using a high-spectral resolution lidar based on iodine absorption filter with a working wavelength 532 nm and have the opportunity of polarization characteristics of the lidar signal. The results from simultaneously observations of particle backscatter and extinction profiles, lidar ratio (extinction to backscatter ratio) and depolarization ratio during on the four annual seasons are presented. We analyzed the seasonal variations of the particle backscatter, extinction and lidar ratio to investigate climatology of aerosol optical properties, and especially lidar ratio, over this region. The experimental results are compared with results obtained over another places and techniques.
In the paper methods and experimental techniques for study of various types of clouds in the PBL (St, Sc, Cu, Stfr, fair weather clouds, etc.) accompanied by the obtained related information are presented and discussed. The abilities of different methods for determination of the cloud base height and its dynamics are also considered. The possibility for determination of the clouds phase composition through analysis of the lidar signal polarization characteristics is shown. The basic physical mechanisms grounding the lidar study of cloud formations and the limits of their applicability are discussed. The algorithms of data processing and desired information extraction are described as well. The studies presented in the paper were carried out using a backscatter aerosol lidar system with a polarization unit and module for the viewing angle variation. The results obtained employing the methods and techniques, subject of the paper, could be summarized as follows: (1) following of the base height of various types of clouds and its dynamics in different atmospheric situations and synoptic conditions, including atmospheric fronts passage; (2) determination of crystal (ice) phase within the volume of different types of clouds; (3) estimation of the density of cloud formations; (4) determination of some microphysical characteristics of the clouds, such as droplets mean size, water content, etc.
The observation of the processes taking place in the entire planetary boundary layer of the atmosphere in the case of stable stratification and during the development of a convective boundary layer correspond thoroughly to the capabilities of a scanning aerosol lidar (SAL) and polarization aerosol lidar (PAL). Recently methods are used allowing automated determination of the maxing layer height, e.g., through the first derivative of the signal, the maximum of its standard deviation, in certain cases through the depolarization ratio (δ) of the signal, etc.
A part of the results obtained during the winter experimental campaign 'LIRADEX'98' are presented. A vertically sounding aerosol lidar and a thermal infrared radiometer were used for joint investigation of low clouds. Both devices were placed at height of about 12 m above the ground and about 25 m apart. Data about the atmospheric parameters were obtained by parallel standard aerological observation. The experimental campaign extended two weeks during November and December, 1998. The data discussed in the presented paper are obtained on December 2, 1998.
The lidar technique used provides simultaneous recording of parallel and cross polarized components of the returned signal at different viewing angles of the receiving optics. The experimental data consist of time series of both polarized components recorded from different distances along the sounding path within the cloud. The auto-correlation functions of both polarization components are calculated using the time series of the lidar signal obtained at different distances. The auto-correlation functions of the parallel component of the lidar signal show two zones within the cloud, where the aerosol backscattering coefficient has close values. The auto- correlation functions of the cross component of the signal reveals the existence of a similar zone, which determines the area which the multiple scattering develops in the same manner. The cross-correlation functions of the parallel and cross components of the polarized signals confirm our suggestions as they show a time delay of approximately 150 ns.
The preliminary results obtained during the experimental campaign `LIRADEX'98' are presented. A vertically sounding aerosol lidar and an infrared optical radiometer were used to investigate low clouds. Both devices were placed at height of about 12 m above the ground and about 25 m apart. Data about the atmospheric parameters were obtained by parallel standard aerological observation. The experimental campaign extended two weeks--from 06.05.1998 to 19.05.1998. The data presented in the paper are from 08.05.1998.
Lidars and widely used for investigations of dense atmospheric objects (fogs, clouds, smoke trails) both for the needs of meteorology and ecology. The polarization studies give additional information about the optical and microphysical properties of the observed objects and phenomena. Two main factors determine the polarization state of the backscattered laser radiation: the shape and size of the scattering particles and the multiple scattering effects. The present work aims at determining the prevailing contribution of one of the factors in different atmospheric situations. Radiative fog and Sc clouds have been investigated by means of polarization aerosol lidar. The multiple scattering contribution was studied by varying the viewing angle of the lidar. On the basis of the lidar data an empirical relation is proposed describing the dependence of the lidar signal depolarization on the viewing angle. On the basis of the particular depolarization coefficient values obtained conclusion is drawn up about the phase composition of the cloud formations.
Lidar investigation of dense atmospheric objects in the planetary boundary layer is of a great interest for both the atmospheric optics and applied meteorology. During recent years ever more attention is paid to the effect of the multiple scattering on the backscattered lidar signals. In experimental aspect two types of lidar systems are developed, namely, (i) on the basis of available polarization lidars by introducing receivers with a variable viewing angle [1,2,3, 1 1] and (ii) specially designed for investigation of the multiple scattering effects [41. The second type of lidars are equipped with high power pulse lasers and multiple-field-ofview receivers ensuring a simultaneous recording of signals at several field-of-views; solid coaxial detectors are used. In the present paper the changes in polarization characteristics of the lidar signals depending on the receiver's viewing angle are experimentally studied in cases offog and St clouds (water-droplet) using a lidar of the first type.
In the paper some polarization investigations of objects and phenomena in the planetary boundary layer of the atmosphere are presented. The observations described were performed by a ground-based lidar over the region of Sofia city where various industrial enterprises exist along with a heavy transport and aerial communications. The changes in the optical characteristics of fog and snow depending on the changes in the microphysical characteristics of the respective objects caused by the meteorological situation changes. The dynamics of the cloud system formation during a warm front advection is observed. The lidar data give possibility of following the base of two of the clouds layers along with the changes in their polarization characteristics. Differences between the optical properties of the aerosol near the clouds base and top are established. The depolarization coefficient changes depending on the penetration depth allows the phase composition of the cloud layers to be determined.
In the paper some results of polarization investigations of various objects and phenomena in the atmospheric planetary boundary layer performed by a ground-based lidar are presented. An attempt is made the frontal zone passing to be followed in more detail. The dynamics of the cloud system formation is observed. Differences between the optical properties of the aerosol near the clouds base and top are established; through the depolarization coefficient changes within the clouds the phase composition of the latter is determined.
In the present work some results of polarization measurements in the planetary boundary layer are reported. The observations described were performed by a ground-based lidar over the region of the Sofia city (where various industrial enterprises exist along with a heavy transport and aerial communications). The data obtained when sounding in different meteorological situations (`clear' atmosphere, rain, fog, snowfall) are considered. Certain differences are established in the depolarization properties of `clear' atmosphere in dependence of the meteorological condition. The developments of fog and snowfall are traced; the effects of the underlying surface are sought when sounding in fog; various types of situations during a snowfall are pointed as well. An attempt is made to follow the development of the processes which proceed during an interaction between air masses with different properties (e.g. a front advection); as a result the formation of the cloud system over the region is traced. Definite differences between the microphysical properties of the aerosol near the clouds (Fmb, Ns) base and top are established as well.
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