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International audience; Lidar techniques represent the most suitable tool to obtain information on the aerosol vertical distribution and therefore to close this kind of observational gap. Lidar networks are fundamental to study aerosol on large spatial scale and to investigate transport and modification phenomena. These are the motivations why EARLINET, the European Aerosol Research Lidar Network, was established in 2000, as a research program funded by the European Commission in the frame of the 5th framework program. After the end of the project, the network activity continued on the base of a voluntary association. At present, EARLINET consists of 25 lidar stations distributed over Europe. On March 2006, the EC Project EARLINET-ASOS (Advanced Sustainable Observation System) started on the base of the EARLINET infrastructure. This infrastructure project will enhance the operation of the network. EARLINET data can contribute significantly to the quantification of aerosol concentrations, radiative properties, long-range transport and budget, and prediction of future trends on European and global scale. It can also contribute to improve model treatment on a wide range of scales and to a better exploitation of present and future satellite data

The international experiment called the European Aqua Thermodynamic Experiment (EAQUATE) was held in September 2004 in Italy and the United Kingdom to validate Aqua satellite Atmospheric Infrared Sounder (AIRS) radiance measurements and derived products with certain ground-based and airborne systems useful for validating hyperspectral satellite sounding observations. A range of flights over land and marine surfaces were conducted to coincide with overpasses of the AIRS instrument on the Earth Observing System Aqua platform. Direct radiance evaluation of AIRS using National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Testbed-Interferometer (NAST-I) and the Scanning High-Resolution Infrared Sounder has shown excellent agreement. Comparisons of level-2 retrievals of temperature and water vapor from AIRS and NAST-I validated against high-quality lidar and dropsonde data show that the 1-K/1-km and 10%/1-km requirements for temperature and water vapor (respectively) are generally being met. The EAQUATE campaign has proven the need for synergistic measurements from a range of observing systems for satellite calibration/validation and has paved the way for future calibration/validation activities in support of the Infrared Atmospheric Sounding Interferometer on the European Meteorological Operational platform and Cross-Track Infrared Sounder on the U.S. NPOESS Prepatory Project platform.

The European Aerosol Research LIdar NETwork (EARLINET) is the first aerosol lidar network on a continental scale with the main goal to provide a comprehensive, quantitative, and statistically significant database for the aerosol distribution over Europe. Next, we present EARLINET along with the main network activities.

The synergistic use of the measurements carried out using active and passive techniques represent a powerful solution to fully exploit the capabilities of each remote sensing techniques and to contemporarily overrun its main limitations. The ground-based facility operational at the CNR-IMAA for the study of the atmosphere is an optimal site where testing possible synergies between active and passive techniques for improving the profiling capabilities of atmospheric key variables, such as aerosol, water vapor and clouds. The combination of the measurements provided by a lidar and a passive sensor is a particularly promising approach because it puts together the high-resolution measurements obtained using a lidar and the operational capabilities typical of passive sensors. In particular, the combination of the Raman lidar and sunphotometry measurements allows to describe the aerosol optical and microphysical properties, supporting the lidar retrievals during daytime and in presence of thick clouds. Moreover, the use of Raman lidar and microwave measurements, integrated using an approach based on the Kalman filter, is an optimal way to provide high-resolution measurements of the tropospheric water vapor in nearly all weather conditions. A strong improvement in the supercooled liquid water retrieval, obtained through the inversion of the microwave brightness temperature, is also achievable using the cloud base height information retrieved using the lidar backscattering ratio profile to constrain the microwave retrieval.

EARLINET-ASOS (European Aerosol Research Lidar Network - Advanced Sustainable Observation System) is a 5-year EC Project started in 2006. Based on the EARLINET infrastructure, it will provide appropriate tools to improve the quality and availability of the continuous observations. The EARLINET multi-year continental scale data set is an excellent instrument to assess the impact of aerosols on the European and global environment and to support future satellite missions. The project is addressed in optimizing instruments and algorithms existing within EARLINET-ASOS, exchanging expertise, with the main goal to build a database with high quality aerosol data. In particular, the optimization of the algorithms for the retrieval of the aerosol optical and microphysical. properties is a crucial activity. The main objective is to provide all partners with the possibility to use a common processing chain for the evaluation of their data, from raw signals to final products. Raw signals may come from different types of systems, and final products are profiles of optical properties, like backscatter and extinction, and, if the instrument properties permit, of microphysical properties. This will have a strong impact on the scientific community because data with homogeneous well characterized quality will be made available in nearly real time.

At CNR-IMAA, an aerosol lidar system is operative since May 2000 in the framework of EARLINET (European Aerosol Research Lidar Network)), the first lidar network for tropospheric aerosol study on continental scale. Since August 2005, PEARL (Potenza EARlinet Lidar) system provides backscatter coefficient profiles at 1064 nm, and independent measurements of extinction and backscatter coefficient profiles at 355 and 532 nm. In addition, measurements of the vertical profiles of aerosol and cloud depolarization ratio at 532 run are obtained by means of the detection of components of backscattered light polarized perpendicular and parallel to the direction of the linearly polarized transmitted laser beam. High quality multi-wavelength measurements (3 backscatter + 2 extinction) plus depolarization measurements make PEARL a reference point for the validation of CALIPSO data products. A direct comparison with CALIPSO data can be carried out for depolarization ratio and aerosol backscatter at 532 and 1064 nm measurements. Furthermore PEARL aerosol extinction measurements at 532 nm and 355 run and backscatter measurements at 355 nm can be used to improve the retrieval of aerosol backscatter coefficient from pure backscatter lidar. Since 14 June 2006, devoted measurements are performed at CNR-IMAA in coincidence of CALIPSO overpasses (maximum 80 kin and 2 hours as spatial and temporal distance). First results of comparison between PEARL and CALIPSO observations are shown.

EARLINET, the European Aerosol Research Lidar Network, is the first aerosol lidar network, established in 2000, with the main goal to provide a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on a continental scale. At present, 23 stations distributed over Europe are part of the network. The EARLINET-ASOS (Advanced Sustainable Observation System) EC Project, starting on the EARLINET infrastructure, will contribute to the improvement of continuing observations and methodological developments that are urgently needed to provide the multi-year continental scale data set necessary to assess the impact of aerosols on the European and global environment and to support future satellite missions. The main objective of EARLINET-ASOS 5-year project, started on 1 March 2006, is to improve the EARLINET infrastructure resulting in a better spatial and temporal coverage of the observations, continuous quality control for the complete observation system, and fast availability of standardized data products. This will be reached by defining and using common standards for instruments, operation procedures, observation schemes, data processing including advanced retrieval algorithms, and dissemination of data. The expected outcome is the most comprehensive data source for the 4-D spatio-temporal distribution of aerosols on a continental scale.

[ 1] A multiyear climatological study of Saharan dust intrusions in the central Mediterranean in terms of aerosol optical parameters vertical profiles is carried out for the first time. Observations are performed at Istituto di Metodologie per l'Analisi Ambientale (IMAA) Raman/elastic lidar station located in Tito Scalo, Potenza (40 degrees 36'N, 15 degrees 44'E), from May 2000 to April 2003, in the framework of European Aerosol Research Lidar Network (EARLINET). Desert dust aerosols are observed between 1.8 and 9 km in 112 days. Mean values within the desert dust layer of 76 Mm(-1), 1.0 Mm(-1) sr(-1) and 0.54 Mm(-1) sr(-1) are observed for aerosol extinction at 355 nm and aerosol backscatter at 355 and 532 nm. Desert dust layer optical depth at 355 nm ranges between 0.001 and 0.68, with a mean of 0.13. The source origin is the central Sahara in about 65% of the cases, the western Sahara in about 31%, and only in four cases the eastern Sahara. The most extended database of Saharan dust lidar ratio data was collected: Values range between 6 and 126 sr following a 3-modal Gaussian distribution centered at 22, 37 and 57 sr. A mean value of 37 sr is found around the center of the Saharan dust layer. At its extremes, where dust particles are mixed to PBL and free troposphere background aerosols, a mean value of 57 sr is found. Finally, low lidar ratio values of about 22 sr are observed when large amount of dust is transported at low altitudes over the Mediterranean Sea.

Lidar technique is the most suitable for high vertical and temporal resolution aerosol profiling. In particular the Raman/elastic lidar combined approach allows independent determination of aerosol extinction and backscatter coefficient without any assumption about their relationship. This technique allows the determination of vertical profiles of the lidar ratio, i.e. the ratio of aerosol extinction and backscatter coefficients. In elastic lidar technique an assumption on the lidar ratio profile is needed for the retrieval of aerosol backscatter coefficient. To improve aerosol backscatter coefficient accuracy in the case of pure elastic backscatter lidar, a climatology of lidar ratio values for specific aerosol types is necessary. Five years of systematic lidar ratio measurements have been collected by means of a Raman/elastic lidar system operational at CNR-IMAA, since May 2000 in the framework of EARLINET, the first lidar network for tropospheric aerosol study on continental scale. The dependence of lidar ratio as a function of the altitude is analysed. A climatological analysis of the lidar ratio measurements in the Planetary Boundary Layer (PBL) and for Saharan dust intrusions is carried out. In addition, lidar ratio measurements concerning forest fires and volcanic eruptions are also analyzed.

The international experiment EAQUATE (European AQUA Thermodynamic Experiment) was held in September 2004 in Italy and in the United Kingdom. The Italian phase, performed in the period 6-10 September 2004, was mainly devoted to assessment and validation of performances of new IR hyperspectral sensors and benefits from data and results of measurements of AQUA and in particular of AIRS. It is also connected with the preparatory actions of MetOp mission with particular attention to calibration and validation of IASI products (as water vapour and temperature profiles), characterization of semitransparent clouds and study of radiative balance, demonstrating the role of ground-based and airborne systems in validation operations. The Italian phase of the campaign was carried out within a cooperation between NASA Langley Research Center, University of Wisconsin, the Istituto di Metodologie per l'Analisi Ambientale (CNR-IMAA), the Mediterranean Agency for Remote Sensing (MARS) and the Universities of Basilicata, Bologna and Napoli. It involved the participation of the Scaled Composites Proteus aircraft (with NAST thermal infrared interferometer and microwave radiometer, the Scanning HIS infrared interferometer, the FIRSC far-IR interferometer), an Earth Observing System-Direct Readout Station and several ground based instruments: four lidar systems, a microwave radiometer, two infrared spectrometers, and a ceilometer. Radiosonde launches for measurements of PTU and wind velocity and direction were also performed as ancillary observations. Four flights were successfully completed with two different AQUA overpasses. The aircraft flew over the Napoli, Potenza and Tito Scalo ground stations several times allowing the collection of coincident aircraft and in- situ observations.

At CNR-IMAA located in Tito Scalo (40°36'N, 15°44'E, 760 m a.s.l.), two lidar systems are systematically operational: the first is devoted to tropospheric aerosol characterization, in the framework of EARLINET, and the second performs water vapour measurements. The aerosol lidar system provides independent measurements of aerosol extinction and backscatter coefficient at 355 nm and at 532 nm, aerosol backscatter profiles at 1064 nm and particles depolarization ratio at 532 nm. The Raman lidar for the water vapor allows the vertical profiling of the water vapour mixing ratio with high spatial and temporal resolution up to the tropopause. The system has been calibrated by means of intensive measurement campaign of simultaneous and co-located radiosonde launches. CNR-IMAA is also provided with a DIAL mobile system for pollutants 3-dimensional spatial distribution. Besides these lidar systems, the CNR-IMAA ground based facility for Earth Observation includes ancillary instruments: a radiosounding system for PTU, ozone and wind measurements; a Sun photometer operative since December 2004 in the framework of AERONET; a 12 channels microwave radiometer for continuous measurements of temperature, relative humidity and water vapor, operative since February 2004; a ceilometer for continuous cloud cover monitoring. Lidar systems together with these ancillary instruments make the CNR-IMAA a heavily instrumented experimental site for integrated observations of aerosols, clouds and water vapor to be used for climatological studies and for the validation of satellite data.

The European AQUA Thermodynamic Experiment was devoted to study atmosphere, ocean and land with high resolution measurements. It consisted of two phases: the first one took place in Italy in the 6-10 September period and the second one in England on 13-22 September. In the framework of the EAQUATE Italian phase, an intensive lidar measurement campaign was performed at CNR-IMAA, sited in Tito Scalo (40°36'N 15°44'E, 760 m a.s.l.). Independent measurements of aerosol extinction and backscatter coefficient at 355nm, and aerosol backscatter coefficient at 532 nm were obtained by means of an elastic\Raman lidar. Another Raman lidar allowed the vertical profiling of the water vapour mixing ratio. Both the lidar systems have high vertical and temporal resolution (15 m - 1 minute), allowing a characterization of the Planetary Boundary Layer as well as of the Free Troposphere also in terms of dynamical behaviour. Ancillary instruments were utilized contemporaneously with lidar measurements. In particular 17 Vaisala radiosondes for PTU measurements were launched during the campaign, 10 of these equipped with RS90 sensors, while 7 utilized RS92 sondes equipped with GSP sensors for wind velocity and direction measurement. Furthermore a 12 channels microwave radiometer providing all around the clock measurements of temperature, relative humidity and water vapour content, was used during the campaign together with a ceilometer for continuous indication of the cloud cover.

Systematic lidar measurements of aerosol backscatter and extinction in the troposphere were performed since May 2000 with the aerosol lidar system operational at IMAA-CNR in Tito Scalo (Potenza) (Southern Italy, 40°36N, 15°44E, 820 m above sea level) in the framework of EARLINET. EARLINET is the first European network of 22 advanced lidar stations operating to provide a quantitative climatological database of the horizontal, vertical and temporal distribution of aerosols over Europe. Aerosol backscatter measurements were performed at both 355 nm and 532 nm, while aerosol extinction coefficient was retrieved from simultaneous N 2 Raman backscatter signals at 386.6 nm. The lidar measurements at IMAA have been performed according to a regular schedule of two night time measurements per week (around sunset) and one daytime measurement per week (around 13:00 UT). Further measurements were devoted to observe special events such as Saharan dust, forest fires and volcanic eruptions. A statistical analysis on climatological aerosol extinction-to-backscatter ratio (lidar ratio) data, covering more than th ree years of systematic lidar observations, has been carried out. These lidar ratio data, in conjunction with an analysis on the air masses backtrajectories, provide information on microphysical properties of the aerosol on a wide range of meteorological conditions. Results obtained starting from both climatological data and special events (Saharan dust and volcanic eruptions) are presented and discussed. Keywords : Lidar, aerosol, Raman, EARLINET, networking

The study of atmospheric aerosol is fundamental in order to get a best comprehension of the atmospheric system and to comprehend how they affect our environment at the local and global levels. Information about aerosol concentration and radiative properties in their ambient environment are indispensable and, in this respect, lidars represent the most powerful tool because their capability to provide information on atmospheric component and parameters with very high spatial and temporal resolutions. Two lidar systems are operational at Istituto di Metodologie per l’Analisi Ambientale of the National Council of Research (IMAA-CNR), Tito Scalo, Potenza, Italy; the first, used in the framework of EARLINET, is able to provide aerosol backscatter coefficient at two wavelengths (355 nm and 532 nm) and extinction coefficient in the UV in the troposphere, and the other, used in the framework of the validation program of ENVISAT, is devoted to measure both tropospheric and stratospheric aerosol in the UV and water vapor up to the tropopause. We present in this paper results obtained starting from three years of systematic aerosol lidar observations and more than one year of water vapor lidar measurements. Both local aerosol and dust transported from the Sahara regions have been characterized.

[1] Results of a lidar measurement campaign performed at IMAA-CNR (Potenza, Italy) during the 2002 Etna volcano eruption, are reported. With combined Raman elastic-backscatter lidar, independent measurements of aerosol extinction and backscatter coefficients at 355 nm are retrieved, whereas aerosol backscatter coefficient at 532 nm is retrieved from elastic lidar signal. A volcanic aerosol layer has been observed in the free troposphere on 1–2 November. AVHRR images show direct plume transport from Etna to Potenza. Optical depth of 0.1 and lidar ratio of 55 sr at 355 nm have been observed at the moment of direct transport. For the first time, a measurement of the lidar ratio for tropospheric volcanic aerosol has been performed. This lidar ratio value and the estimation of the wavelength dependence of the aerosol backscatter coefficient of 2.4 indicate the presence of young sub-micron sulfate particles, a low soot content, and the absence of large ash particles.

An intensive aerosol and water vapour measurement campaign, started on June 2002, is in progress at IMAA in Tito Scalo (PZ) (Southern Italy, 40°36'N, 15°44'E, 820 m above sea level) in the frame of the validation program of ENVISAT. Systematic measurements, using both active and passive ground based instruments, will be performed for a period of 12 months, in coincidence with ENVISAT overpasses. A Raman lidar system is used to perform both aerosol and water vapour measurements; aerosol backscatter and extinction coefficients are retrieved from simultaneous elastic signals at 355 nm and inelastic N2 Raman backscatter lidar signals at 386.6 nm, whereas, water vapour mixing ratio measurements are retrieved from simultaneous H2O and N2 Raman signals. A sun-photometer based on a Mechelle spectrometer is used to measure direct solar irradiance in the wavelength range 300 ÷ 1100 nm and a Fourier infrared spectrometer is used to measure vertical sky radiance in the range 500 ÷ 3000 cm-1. All the observations are complemented with radio-sonde launches. Two measurements per week are scheduled for the first six months of the validation campaign, while one measurement per week is scheduled for the last six months. First results of the measurement campaign are presented.

A statistical analysis on two years of systematic lidar measurements of aerosol backscatter and extinction, performed in Tito Scalo (Potenza) within EARLINET, shows the seasonal variation and the large variability of the aerosol properties.

A differential absorption lidar system (DIAL) based on a continuously tunable optical parametric amplifier (OPA) pumped by a Nd : YAG laser (200 mJ at λ=355 nm) operating at a maximum pulse repetition rate of 100 Hz has been developed. The system provides continuously tunable coherent radiation in the Visible–near IR range (0.4–2.5 μm), allowing to perform DIAL measurements in a spectral region where most of atmospheric constituents and pollutants display absorption lines. The spectral width of the OPA system is line-narrowed by using a master oscillator dye laser as seeder, achieving a linewidth of 0.04 cm−1 (FWHM), a spectral purity larger than 99% and a frequency stability better than 1 pm h−1, with an output energy in the IR of 1–10 mJ. The OPA system was used to perform DIAL measurements in the lower troposphere. Preliminary results in terms of water vapor content and aerosol backscattering profiles are presented and discussed.

High temporal and spatial resolution measurements by both space-borne and ground-based instruments are therefore necessary to monitor atmospheric water vapor for climate purposes. Lidar techniques can accomplish ground-based measurements of atmospheric water vapor with high space and time resolution. A lidar system capable to perform simultaneous measurements of atmospheric water vapor and aerosols has been developed in Potenza, Southern Italy, in the context of a cooperation between the Universita della Basilicata and Istituto di Metodologie Avanzate di Analisi Ambientale. An intensive measurement campaign was performed during 1997 in Potenza aimed to the simultaneous application of the Raman and DIAL techniques for water vapor ground- based lidar measurements. Raman and DIAL humidity measurements performed during 1997 in Potenza aimed to the simultaneous application of the Raman and DIAL techniques for water vapor ground-based lidar measurements. Raman and DIAL humidity measurements performed at night in the Planetary Boundary Layer have been compared with simultaneous radiosonde data obtained from both free and captive balloons. The agreement among Raman, DIAL and radiosonde data is found to be within 30 percent up to approximately 1.5 km. Results from this measurement campaign will be reported and discussed in this paper.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A study of the transmissivity in the spectral UV range for two sites (Napoli-Italy urban area, 41°N 16°E — 0 m a.s.1., andPotenza-Italy rural area, 4O03 'N 15°44'E — 820 m a.s.1.), with different pollutant content, has been performed. Resultsobtained from measurements covering a period of five years (1994-1998) are shown and the variability of the transmissivityprofile and its time evolution during a night has been correlated to the water vapor content at the lower height. The aerosoloptical thickness has been retrieved from lidar measurements with an evident cloud extinction and the cloud lidar ratio hasbeen estimated from the independent simultaneous measurements of the aerosol extinction and backscattering coefficients.Keywords: Lidar Atmospheric Transmissivity, cloud extinction, optical thickness, variability. 1. INTRODUCTION Lidar systems are employed to monitor the chemical and physical properties of the Earth's atmosphere. By using differentlidar techniques, it is possible to obtain atmospheric temperature and density profiles, water vapor and trace gas content,optical properties of both tropospheric and stratospheric aerosols and finally microphysical properties of clouds. In all thesecases an accurate estimation of atmospheric transmissivity for laser radiation is necessary. In fact, the energy loss of a laserbeam propagating through the atmosphere is the result of simultaneous phenomena such as molecular absorption andmolecular and particulate scattering. These phenomena are highly dependent from both laser wavelength and meteorologicalconditions. Atmospheric transmissivity measurements allow to take into account these phenomena and to correct adequatelythe lidar equation for every measured atmospheric parameter. Atmospheric transmissivity measurements are also of interestin meteorology, in the physics of clouds and in the chemistry of the atmosphere and represent a key parameter in thedevelopment of Earth radiative equilibrium models and to study the greenhouse effect. Atmospheric transmissivityrepresents a non-selective but sensitive index of the air quality, which provides information on the complessive amount oftrace gases and particulate present in the atmosphere.The evaluation ofthe atmospheric transmissivity profile is very important in all the optical regions, although the dependenceon the wavelength of the backscattered energy from the atmosphere limits the use of the lidar technique in the VIS-UVrange. Generally the atmospheric transmissivity study is realised by means of measurements of the extinction of a laserbeam propagating through the atmosphere. Several authors have measured the absorption and the scattering contributions toatmospheric extinction'4. In this case the transmissivity profile is obtained from the lidar equation by integrating the totalextinction coefficient, taking into account the effects ofboth molecular and aerosol contribution.In the present work we use the N2 Raman lidar signal to retrieve the atmospheric transmissivity profile directly, so obtainingan integrate measurement of the extinction coefficient, without accomplishing the integral calculation5. Results obtainedfrom measurements covering a period of five years (1 994- 1998) are discussed and data obtained in two different sites,Napoli, urban area with very high pollutant content, and Potenza, rural area with a lower atmospheric pollution, arecompared. Moroever we report a study of the variability of the transmissivity profile and its time evolution during a night.The results are also correlated with the time evolution of the water vapor content in the lower atmosphere. Finally lidarmeasurements of cloud extinction and the aerosol optical thickness are presented.

A lidar system capable to perform simultaneous measurements of atmospheric water vapor and aerosols have been developed in Tito Scalo, in the context of a cooperation between Universita della Baslicata and Istituo di Metodolgoie Avanzate di Analisis Ambientale. Aerosol observations by lidar in the nocturnal boundary laser (NBL) have been performed in the period 20 January- 20 February 1997, Radiosondes were launched during the measurement campaign simultaneously to lidar operation. Lidar observations have been sued to retrieve aerosol properties and dimensional characteristics. Aerosol sizes are determined by comparison measured and theoretical values of (beta) A,723(z)/(beta) A,355(z), with (beta) A,723(z) and (beta) A,355(z) being the aerosol backscattering coefficient at 723.37 and 355 nm, respectively. Furthermore, lidar and radiosonde data have been compared in order to study the NBL vertical structure and evolution. Lidar measurements of (beta) A,723(z) are compared with simultaneous radiosonde data expressed in terms of potential temperature and relative humidity, with particular emphasis on the estimate of the residual layer height from both lidar and radiosonde data. Results from the present measurements campaign will be reported and discussed in this presentation.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

In this paper we present an intercomparison between ground based lidar, radiosonde and satellite atmospheric water vapor measurements. Comparisons expressed in terms of water vapor profiles, obtained by Raman lidar and simultaneous ballonborne radiosonde, are reported and discussed. The deviation between the two profiles is smaller than 10 percent up to an altitude of 5 km. Furthermore, the intercomparison between lidar and radiosonde data and between lidar and satellite data is performed also in terms of water vapor columnar content. The agreement between lidar and radiosonde columnar content is better than 4 percent. Water vapor contour map are showed in order to demonstrate the high spatial and temporal variability of water vapor in the lower atmosphere. Difficulties in comparing lidar and satellite water vapor columnar contents associated to H2O spatial and temporal variability are discussed in the paper.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A lidar system able to measure simultaneously different atmospheric parameters in the lower troposphere have been developed and used to monitor the air quality of an industrial area of Southern Italy. The system is based on a Nd:YAG laser pumping two dye lasers, and on two Newtonian telescopes, equipped with periscopes for 3D mapping. One telescope is devoted to DIAL and the other to the N2 and H2O Raman channels, and to the elastic channels at 1064 nm, 532 nm and 355 nm. Aerosol backscattering coefficients measurements have evidenced the presence of an aerosol layer. The laser has been characterized by measuring its temporal evolution and by correlating it with atmospheric transmissivity profiles measured at different zenithal angles. Preliminary results of atmospheric pollutants concentration measurements by UV DIAL technique are also reported.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new multiparametric lidar system spanning from UV to mid IR is presently under testing. The system is based on twoOptical Parametric Amplifier (OPA) lasers pumped by a Nd:YAG laser operating at a maximum pulse repetition rate of 100Hz. OPA lasers represent a new design for coherent radiation sources continuously tunable in the UV - JR range. The largerange of tunability of OPA lasers allows to perform Differential Absorption Lidar (DIAL) measurements in a spectral regionwhere most of atmospheric pollutants display absorption lines. The system has been designed to deliver simultaneously in theatmosphere the Nd:YAG fundamental and its harmonics (II and III) as well as the four output beams of the two OPA lasers.The return signals, collected by means of two Newtonian telescopes, can be used to retrieve information on: atmosphericaerosols, water vapour and pollutants concentration, atmospheric temperature, density and transmissivity profiles. In thispaper a detailed description of the system is reported. Moreover, some results obtained by a multiparametric system (basedon a Nd:YAG pumped dye laser) are reported to show the capabilities of a multiwavelength lidar system.Keywords: Lidar, OPA laser, JR.

The present paper is devoted to the description of two distinct multiparametric lidar system presently under development. The first system is based on a Nd:YAG laser pumping a dye laser equipped with a dual wavelength device. The second lidar system is based on two optical parametric oscillator (OPO) lasers pumped by a Nd:YAG laser operating at a pulse repetition rate of 100 Hz. OPO lasers represent a new design for coherent radiation sources continuously tunable in the UV -- near IR range (up to 2 micrometer). This allows us to perform differential absorption lidar (DIAL) measurements in a spectral region where most of atmospheric pollutants display absorption lines. The selection of the wavelengths to be used for DIAL measurements is a non trivial task. In particular, a method to select the optimal (lambda) ON and (lambda) OFF has been developed and applied to several molecular gases. Both systems have been designed to carry out simultaneous measurements of atmospheric aerosols, water vapor profiles, temperature and density profiles, atmospheric transmissivity, and atmospheric pollutants concentration.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We have characterized experimentally the trapping of resonance radiation in an effusive He beam produced by a needle injector. In order to take into account the influence of secondary effects, such as collisions, on the trapping process, the measurements were carried out by investigating the line intensity dependence on the atomic density of transitions , and in the visible and and in the vacuum ultraviolet region of the helium spectrum. The comparison between visible and vacuum ultraviolet spectra allowed us to characterize the excitation process and to evaluate the contribution of collisional effects. We have calculated the escape factor, g, as a function of the atomic density and of the distance from the needle injector, i.e. along the beam path. The results were also compared with the Holstein and Phelps approach describing the trapping process in terms of an effective radius, . Our results show that in the case of an effusive beam, the effective radius is of the order of the effusive beam radius, namely .

We report on TOF mass spectrometric analysis of plasmas produced by laser ablation on Al targets. We obtained mass spectra of ionized species in the UV ({ce:inline-formula}λ = 355nm{/ce:inline-formula}) and in the visible ({ce:inline-formula}λ = 532nm{/ce:inline-formula}) and at high laser fluences (1–80 J cm−2). The total ion yield, the relative abundance of different charged species and the laser fluence threshold for the appearance of specific ions as a function of energy density were measured.

In a previous publication [Appl. Opt. 43, 961 (2004)], One of the figures on page 973 was presented inaccurately, as was the surname of the first author. These inaccuracies are corrected here. (C) 2004 Optical Society of America

In the framework of the European Aerosol Research Lidar Network to Establish an Aerosol Climatology (EARLINET), 19 aerosol lidar systems from 11 European countries were compared. Aerosol extinction or backscatter coefficient profiles were measured by at least two systems for each comparison. Aerosol extinction coefficients were derived from Raman lidar measurements in the UV (351 or 355 nm), and aerosol backscatter profiles were calculated from pure elastic backscatter measurements at 351 or 355, 532, or 1064 nm. The results were compared for height ranges with high and low aerosol content. Some systems were additionally compared with sunphotometers and starphotometers. Predefined maximum deviations were used for quality control of the results. Lidar systems with results outside those limits could not meet the quality assurance criterion. The algorithms for deriving aerosol backscatter profiles from elastic lidar measurements were tested separately, and the results are described in Part 2 of this series of papers [Appl. Opt.43, 977–989 (2004)]. In the end, all systems were quality assured, although some had to be modified to improve their performance. Typical deviations between aerosol backscatter profiles were 10% in the planetary boundary layer and 0.1 × 10-6 m-1 sr-1 in the free troposphere.

A strategy for European Aerosol Research Lidar Network (EARLINET) correlative measurements for Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) has been developed. These EARLINET correlative measurements started in June 2006 and are still in progress. Up to now, more than 4500 correlative files are available in the EARLINET database. Independent extinction and backscatter measurements carried out at high-performance EARLINET stations have been used for a quantitative comparison with CALIPSO level 1 data. Results demonstrate the good performance of CALIPSO and the absence of evident biases in the CALIPSO raw signals. The agreement is also good for the distribution of the differences for the attenuated backscatter at 532 nm ((CALIPSO-EARLINET)/EARLINET (%)), calculated in the 1-10 km altitude range, with a mean relative difference of 4.6%, a standard deviation of 50%, and a median value of 0.6%. A major Saharan dust outbreak lasting from 26 to 31 May 2008 has been used as a case study for showing first results in terms of comparison with CALIPSO level 2 data. A statistical analysis of dust properties, in terms of intensive optical properties (lidar ratios, Ångström exponents, and color ratios), has been performed for this observational period. We obtained typical lidar ratios of the dust event of 49 ± 10 sr and 56 ± 7 sr at 355 and 532 nm, respectively. The extinction-related and backscatter-related Ångström exponents were on the order of 0.15-0.17, which corresponds to respective color ratios of 0.91-0.95. This dust event has been used to show the methodology used for the investigation of spatial and temporal representativeness of measurements with polar-orbiting satellites. Copyright 2010 by the American Geophysical Union.

A lidar system with the characteristic of simultaneously monitoring several atmospheric parameters such as atmospheric aerosols load, water vapor content, temperature and density, atmospheric transmissivity, and atmospheric pollutants concentration, has been realized. This system, based on two OPA lasers pumped by a Nd:YAG laser operating at maximum repetition rate of 100 Hz, is primary dedicated to tropospheric measurements. The system is continuously tunable over the spectral range 410 nm - 2500 nm, allowing DIAL measurements in a region where most of atmospheric pollutants display absorption lines. Preliminary measurements have been carried out. We report the simultaneous temporal evolution of the aerosol backscattering coefficient profiles at 355 nm and 829 nm in a rural area. A method to select optimal couples of wavelength for DIAL measurements in the near/mid IR spectral region has been developed. A sensitivity analysis has been carried out in order to find the minimum detectable concentration, that has been demonstrated of the order of few tenths up to few part per million in volume.

During the ADRIMED (Aerosol Direct Radiative Impact on the regional climate in the Mediterranean region) special observation period (SOP-1a), conducted in June 2013 in the framework of the ChArMEx (Chemistry-Aerosol Mediterranean Experiment) project, a moderate Saharan dust event swept the Western and Central Mediterranean Basin (WCMB) from west to east during a 9-day period between 16 and 24 June. This event was monitored from the ground by six EARLINET/ACTRIS (European Aerosol Research Lidar Network/Aerosols, Clouds, and Trace gases Research Infrastructure Network) lidar stations (Granada, Barcelona, Naples, Potenza, Lecce and Serra la Nave) and two ADRIMED/ChArMEx lidar stations specially deployed for the field campaign in Cap d’en Font and Ersa, in Minorca and Corsica Islands, respectively. The first part of the study shows the spatio-temporal monitoring of the dust event during its transport over the WCMB with ground-based lidar and co-located AERONET (Aerosol Robotic Network) Sun-photometer measurements. Dust layer optical depths, Ångström exponents, coarse mode fractions, linear particle depolarization ratios (LPDRs), dust layer heights and the dust radiative forcing estimated in the shortwave (SW) and longwave (LW) spectral ranges at the bottom of the atmosphere (BOA) and at the top of the atmosphere (TOA) with the Global Atmospheric Model (GAME), have been used to characterize the dust event. Peak values of the AERONET aerosol optical depth (AOD) at 440 nm ranged between 0.16 in Potenza and 0.37 in Cap d’en Font. The associated Ångström exponent and coarse mode fraction mean values ranged from 0.43 to 1.26 and from 0.25 to 0.51, respectively. The mineral dust produced a negative SW direct radiative forcing at the BOA ranging from −56.9 to −3.5 W m−2. The LW radiative forcing at the BOA was positive, ranging between +0.3 and +17.7 W m-2. The BOA radiative forcing estimates agree with the ones reported in the literature. At the TOA, the SW forcing varied between −34.5 and +7.5 W m−2. In seven cases, the forcing at the TOA resulted positive because of the aerosol strong absorbing properties (0.83 < single-scattering albedo (SSA) < 0.96). The multi-intrusion aspect of the event is examined by means of air- and space-borne lidar measurements, satellite images and back trajectories. The analysis reported in this paper underline the arrival of a second different intrusion of mineral dust observed over southern Italy at the end of the considered period which probably results in the observed heterogeneity in the dust properties., Spanish Ministry of Economy and Competitiveness (project TEC2012-34575 and TEC2015-63832-P), Science and Innovation (project UNPC10-4E-442), Andalusia Regional Government through projects P12-RNM-2409 and P10-RNM-6299

Lidar observations of atmospheric aerosols have been performed at IMAA-CNR, Tito Scalo, Southern Italy, during the last two last eruptive events of Etna volcano in July-August 2001 and October-December 2002 periods. For both campaigns, some anomalous layers have been observed at 4 km of height above sea level. Anomalous values of lidar ratio, i.e. extinction to backscatter ratio, respect to those typically measured at IMAA, reveal the presence of aerosol with a different chemical composition and size distribution. Such values have been ascribed to the presence of Etna emitted aerosol.

An intercomparison of the algorithms used to retrieve aerosol extinction and backscatter starting from Raman lidar signals has been performed by 11 groups of lidar scientists involved in the European Aerosol Research Lidar Network (EARLINET). This intercomparison is part of an extended quality assurance program performed on aerosol lidars in the EARLINET. Lidar instruments and aerosol backscatter algorithms were tested separately. The Raman lidar algorithms were tested by use of synthetic lidar data, simulated at 355, 532, 386, and 607 nm, with realistic experimental and atmospheric conditions taken into account. The intercomparison demonstrates that the data-handling procedures used by all the lidar groups provide satisfactory results. Extinction profiles show mean deviations from the correct solution within 10% in the planetary boundary layer (PBL), and backscatter profiles, retrieved by use of algorithms based on the combined Raman elastic-backscatter lidar technique, show mean deviations from solutions within 20% up to 2 km. The intercomparison was also carried out for the lidar ratio and produced profiles that show a mean deviation from the solution within 20% in the PBL. The mean value of this parameter was also calculated within a lofted aerosol layer at higher altitudes that is representative of typical layers related to special events such as Saharan dust outbreaks, forest fires, and volcanic eruptions. Here deviations were within 15%.

Level 2.0 data (processed output) and simulation data for the AMT EARLINET special issue paper "Experimental techniques for the calibration of lidar depolarization channels in EARLINET"

The availability of new laser sources that are tunable in the IR spectral region opens new perspectives for differential absorption lidar (DIAL) measurements. A region of particular interest is located in the near IR, where some of the atmospheric pollutants have absorption lines that permit monitoring of emissions from industrial plants and in urban areas. In DIAL measurements,the absorption lines for the species to be measured must be carefully chosen to prevent interference from other molecules, to minimize the dependence of the absorption cross section on temperature, and to optimize the measurements with respect to the optical depth. We analyze the influence of these factors and discuss a set of criteria for selecting the best pairs of wavelengths (lambda (ON) and lambda (OFF)) to be used in DIAL measurements of several molecular species (HCl, CO, CO2, NO2, CH4, H2O, and O-2). Moreover, a sensitivity study has been carried out for selected lines in three different regimes: clean air, urban polluted air, and emission from an incinerator stack. (C) 2000 Optical Society of America OCIS codes: 280.1910, 280.1120, 280.0280, 280.3640.

Aerosol observations by lidar in the nocturnal boundary layer (NBL) were performed in Potenza, Southern Italy, from 20 January to 20 February 1997. Measurements during nine winter nights were considered, covering a variety of boundary-layer conditions. The vertical profiles of the aerosol backscattering coefficient at 355 and 723.37 nm were determined through a Klett-modified iterative procedure, assuming the extinction-to-backscattering ratio within the NBL has a constant value. Aerosol average size characteristics were retrieved from almost simultaneous profiles of the aerosol backscattering coefficient at 355 and 723.37 nm, the measurements being consistent with an accumulation mode radius not exceeding 0.4 µm. Similar results in terms of aerosol sizes were obtained from measurements of the extinction-to-backscattering ratio profile at 355 nm performed on six nights during the measurement campaign. Backscattering profiles at 723.37 nm were also converted into profiles of aerosol liquid water content.

The lidar group in Potenza has almost 10 years' experience in the field of lidar research. Important results have been accomplished both in aerosol and water vapour research. The lidar system in Potenza has acquired different confi gurations during the years, always preserving the capability to accomplish two wavelength aerosol and water vapour Raman measurements. An important up-grade was the introduction of a water vapour DIAL channel in 1997. The lidar system in Potenza has been involved in several aerosol and water vapour measurement campaigns: stratospheric aerosol measurement campaign (1994-1995); LITE correlative measurement campaign (September 1994); Water Vapour Intensive Observation Period (January-February 1997); EARLINET project (since February 2000). A second lidar system, primarily dedicated to water vapour Raman measurements, is under development and starting January 2002 will go through an intensive observation period dedicated to the validation of sensors on-board ENVISAT (principally GOMOS, MIPAS and SCIAMACHY). This paper summarises some of the major results accomplished, as well as expected results from the forthcoming campaigns.

In this paper, characterization of the optical and microphysical properties of extremely fresh biomass burning aerosol is presented. This work aims to characterize, for the first time to our knowledge, freshly formed smoke particles observed only a few minutes after they were emitted from a nearby forest fire. The smoke particles were detected by combining passive (sun-photometer) and active (Raman lidar) techniques. On 14 August 2021, an EARLINET (European Aerosol Research Lidar Network) multi-wavelength Raman lidar and a co-located AERONET sun-photometer in Potenza, South Italy, observed an extremely fresh smoke plume. The lidar measurements, carried out from 22:27 to 02:16 UTC, revealed a thick biomass burning layer below 2.7 km. The particle depolarization ratio at 532 nm was 0.025, and lidar ratios at 355 and 532 nm were, respectively, 40 and 38 sr. The mean value of the Ångström exponent was 1.5. The derived size distribution was bimodal with a peak at 0.13 µm, an effective radius mean value of 0.15 µm, and a single scattering albedo of 0.96 at all wavelengths. The real part of the refractive index was 1.58 and the imaginary was 0.006. The AERONET measurements at 5:34 UTC confirmed the lidar measurements.

In September 2003, the Lidar Working Group (LWG) of the Network for Detection of Stratospheric Change (NDSC) initiated an extensive project to compare the ozone and temperature algorithms used within NDSC. This initiative, referred to later as Algorithm Intercomparison Initiative (A2I), uses simulated lidar signals to test and compare various parts of the ozone and temperature lidar algorithms. In addition to the fact that it meets the requirement of the NDSC protocols, this exercise allows the detailed assessment, by all the participants, of some of the sources and magnitudes of various uncertainties associated with the algorithms, and/or with the theoretical assumptions made in these algorithms. The outcome of the A2I is to try to find common grounds in the way ozone and temperature can be retrieved in order to reduce and possibly eradicate discrepancies due to algorithm issues alone. Specific issues such as homogenizing the choice of Rayleigh extinction cross-sections, ozone absorption cross-sections, a priori information, and the definition of the vertical resolutions are among the primary targets of the A2I outcome.