This PDF file contains the front matter associated with SPIE Proceedings Volume 6750, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

The fluorescence lidar imaging technique turns particularly useful for the control of monuments. The investigated topics range from the detection of biodeteriogens to the characterization of stones and other masonry or restoration materials, such as protective treatments. In addition, the fluorescence lidar imaging is a non-destructive technique offering the possibility of being carried out in situ without the use of scaffolding that, beside being costly, limits the access to the monument and its use. This paper presents the main technical features of a new fluorescence imaging lidar system specifically developed for the diagnostics on the cultural heritage, whose operative conditions include outdoor and indoor environments, and the possibility of monitoring vaults and ceilings. This fluorescence lidar prototype is mainly composed of a Q-switched, tripled frequency Nd:YAG laser (@355 nm), a 1 m focal length Newtonian telescope and a 300 mm focal length spectrometer coupled to an intensified, gated 512 x 512 CCD detector. Imaging is carried out via a scanning system realized with a computer controlled mirror. The lidar prototype includes also a target pointing system for referencing the acquired fluorescence images on the target.

Airborne depth sounding lidar has proven to be a valuable sensor for rapid and accurate sounding of shallow areas. The received lidar pulse echo contains information of the sea floor depth, but also other data can be extracted. We currently perform work on bottom classification and water turbidity estimation based on lidar data. In this paper we present the theoretical background and experimental results on bottom classification. The algorithms are developed from simulations and then tested on experimental data from the operational airborne lidar system Hawk Eye II. We compare the results to field data taken from underwater video recordings. Our results indicate that bottom classification from airborne lidar data can be made with high accuracy.

A novel ultraviolet laser is demonstrated using a dual wavelength Nd:YAG oscillator, sum frequency and second harmonic process. Synchronous pulses at 1.052 and 1.319 micrometers are amplified, mixed and subsequently doubled, producing pulses at 0.293 micrometers. An attractive feature of this laser design is that it is line tunable. With a properly designed resonator, a potential of 44 possible ultraviolet laser transitions can be operated, resulting in a line tunable UV laser in the wavelength range 0.263 to 0.339 micrometers.

We report a Tm3+/Yb3+-doped tellurite fibre laser operating at wavelengths in the range 1879 - 1994 nm. Two different pump schemes have been demonstrated for this laser: a 1088 nm Yb3+-doped silica fibre laser simultaneously pumping the Tm3+: 3H5 and Yb3+: 2F5/2 levels, and a 1610 nm Er3+/Yb3+-doped silica fibre laser directly pumping the Tm3+: 3F4 upper laser level. For the 1610 nm pumping, a slope efficiency of 76% has been achieved in a 32 cm long fibre which is very close to the Stoke efficiency limit of ~80%. An output power of 283 mW has also been achieved, but with no signs of saturation or fibre damage suggesting that higher output powers should be possible. For the 1088 nm pumping there is very strong pump ESA resulting in bright blue (480 nm) and near-IR (800 nm) emission and this limits the achievable slope efficiency, which in this case was a maximum of 10% for a 16 cm long fibre. With this pump scheme, the highest observed output power was 67 mW, and further power scaling was limited due to the intense ESA and thermal damage to the pump end of the fibre. Lasing has been achieved in <10 cm lengths of this fibre making this material a promising candidate for ultra compact medium power mid-IR laser sources for range-finding, medical and atmospheric monitoring and sensing applications.

Originally developed for telecommunications, fiber lasers are now becoming new effective sources for coherent lidars allowing new instruments to be designed. The advent of the double clad fiber, along with advances in semiconductor pump diode sources, have allowed rapid power scaling of both pulsed and CW fiber sources. The unique capabilities of fiber sources, coupled with significant commercial and academic progress in implementation, have driven fiber technology to enter active remote sensing markets as signal sources and amplification stages for direct detection lidars and coherent lidars as well. Some interesting fiber lasers benefit from a good transmission in the near infrared spectral band. However, useful wavelengths have to be tuned between absorption H20 and CO2 lines. Eye safety may be an issue for atmospheric lidars. Above 1.4 µm, an eye-safe operation is possible even with multi-watt lasers. Low power fiber lasers using single mode fibers have a good spatial quality. However, higher power lasers and amplifiers need larger fiber cores, to store enough energy and to avoid non linear effects. Trade-off between high power, single mode operation, stable polarization and spectral quality need to be considered for coherent lidars.

We report the development of a 355-nm lidar system for short-range wind speed measurements, using a fringe-imaging Michelson interferometer as a spectral analyzer. The instrument principle is to deduce the wind speed from the phase variations of the two-wave interference pattern provided by the interferometer. A laboratory demonstrator has been realized, which was designed in an original way to minimize the sensitivity to phase fluctuations caused by thermo-mechanical disturbances and laser drifts. An accurate signal processing has been developed, providing with estimates of five fringe parameters: intensity, contrast, periodicity, angular orientation, and phase. It is implemented in two steps: the first step uses a Fourier transform analysis and the second step a maximum-likelihood estimator. To validate the instrument principle, measurement method and signal processing alltogether, a calibrated speed measurement experiment has been performed on hard target, for which the results are shown.

Recently, there has been significant interest in lidar signal-to-noise ratio (SNR) improvements, particularly for lidar daytime operations. Previously, we devised in the remote sensing laboratory at the City College of New York a polarization discrimination technique to maximize lidar detected SNR taking advantage of the natural polarization properties of scattered skylight radiation to track and minimize detected sky background signal (BGS). This tracking technique was achieved by rotating, manually, a combination of polarizer and analyzer on both the lidar transmitter and receiver subsystems, respectively. The polarization orientation at which the minimum BGS occurs, follows the solar azimuth angle, even for high aerosol loading. This has been confirmed, in our previous work, both theoretically, assuming single scattering theory, and experimentally. In this paper, a design to automate the polarization discrimination technique by real time tracking of the azimuth angle to attain the minimum BGS is presented. We introduce a feedback control system to track the minimum BGS by rotating the detector analyzer and the transmission polarizer simultaneously to maximize the SNR and attainable lidar ranges, thus achieving the same results as would be done manually. Analytical results for New York City are summarized and an approach for applying the proposed design globally is investigated.

The mixing layer (ML) provides a vertical atmospheric barrier and its height has become an important parameter in meteorology and air quality control. In locating the mixing layer using Lidar it has always to be considered that the signals may be biased by noise and the mixing layer itself can contain more than a single layer. In previous studies use was made of the fact that the main part of aerosols are located within the mixing layer and outside this layer, in the so called free atmosphere, the concentration of aerosols decreased significantly. This leads to a sharp change of the backscattering signal at the boundary layers. In this paper an algorithm is presented that determines the height of the mixing layer (MLH) by an intensive analysis of the global and local maxima of the Lidar signal and its first derivative. The algorithm searches for a maximum of the backscatter signal followed by a minimum in the first derivative. The results are compared with the MLH calculated by a model.

We propose a new approach to range-resolved remote gas sensing in the atmosphere based on a combination of a DIAL and tunable-laser diode spectroscopy (TDLS) methods. To add range-resolving capabilities to a TDLS sensor we propose to arrange a group of retroreflectors (RRs) dividing an absorption path into adjacent measurement sections similar to those utilized by conventional DIAL systems. We implemented two techniques for the interrogation of the RRs: 1) scanning a beam of a continuous-wave laser over RRs sequentially; 2) using a time delay between returns from different RRs illuminated with a pulsed laser. We employed scanning technique with a vertical-cavity surface-emitting laser (VCSEL) operating near 1389 nm. A single-pulse interrogation method was demonstrated with a 10.9-&mgr;m quantum cascade laser (QCL) suitable for detection of ammonia, ethylene and water vapor in the atmosphere. Gas sensing and ranging was performed over distances varying from ~ 1 m up to ~ 1 km. Using VCSEL we attained a 0.5-s time resolution in gas concentration profiling with a 10-cm spatial resolution. Minimum interrogation time of a group of RRs was ~ 9 ms. A new generation of differential absorption LIDARs can be developed for range-resolved gas sensing in the atmosphere over distances up to ~ 1 km. The instruments can be used for a variety of applications ranging from fencing industrial areas to monitor fluxes of atmospheric pollutants to continuous air quality control in populated areas

A measurement approach for estimating the emission flux by a surface-distributed source, based on the use of IR laser measurements over optical links and atmospheric diffusion models is presented. An ad hoc disposition of the optical links close to the emission area allows to measure gas concentration over a closed surface corresponding to an air volume that covers the whole emission area. The real time concentration measurements over this closed surface, associated to suitable diffusion models, allow us to estimate the emission flux of the area under exam. The diffusion model to be applied strictly depends on the current atmospheric conditions, therefore it requires the knowledge of the main atmospheric parameters. In this paper we present some simulation results about a system for the surface flux monitoring assuming the faces of a parallelepiped the surfaces interested by laser measurements. The closed surface is therefore defined by 5 of its sides, while the 6th is the emission surface. We discuss some estimation results using diffusion models where the air diffusion and transportation phenomena are due mainly to the wind strength.

An optical parametric amplifier has been developed to generate tunable 1570 nm radiation from a 1064 nm pump at high efficiency. A micropulse Nd:YAG operating with an average power of 2 watts (10 kHz) is used to pump a PPLN crystal injection seeded by two CW distributed feedback lasers: one at 1570.824 nm and the second at 1570.973 nm. A two stage amplification process has demonstrated a conversion efficiency of ~28% from the pump into the signal wavelength. The 1-nanosecond signal has a measured time-averaged jitter of <40 MHz.

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.

Multiwavelength Raman lidar observations have matured into a powerful tool for the vertical resolved characterization of optical and microphysical properties of atmospheric aerosol particles. Raman lidars that operate with laser pulses at three wavelengths are the minimum requirement for a comprehensive particle characterization. Parameters that are derived with such systems are particle backscatter and extinction coefficients, and particle extinction-to-backscatter (lidar) ratios. Effective radius and complex refractive index can be derived with inversion algorithms. In the past ten years we carried out regular observations over Leipzig, Germany, with multiwavelength Raman lidar. We could establish a time series of important aerosol properties. For instance, we find that pollution layers are present in the free troposphere in more than 30% of our observations in each year. These layers result from long-range transport of, e.g., forest-fire smoke from North America and Siberia, anthropogenic pollution from North America, Arctic haze from North polar areas, and mineral dust from the Sahara. Observations were also carried out with our mobile six-wavelength Raman lidar during several international field campaigns since 1997. Those data allow us to establish a first comprehensive overview on the vertical distribution of optical and microphysical particle properties in different areas of the world.

The properties of aerosol particles are highly variable, both in time and space. This refers to the number density, the microphysical properties (size distribution, refractive index, effective radius), and to the height distribution. In most cases the actual properties are not known. Using lidar data together with models can help improve the knowledge regarding the particulate atmospheric constituents which affect local radiative forcing, the radiation balance of the earth, and thus climate. This paper presents an attempt to integrate elastic backscatter lidar data in OPAC software package in order to find the most realistic aerosol vertical distribution and their optical and microphysical characteristics. The necessity to reduce the variability of naturally occurring aerosols to typical cases, but without neglecting possible fluctuations, is achieved in OPAC by the use of a dataset of typical internally mixed aerosol components. In addition, any mixtures of the basic components can be used to calculate the overall optical parameters. Experimental or modeled meteorological profiles (temperature, pressure, relative humidity) in complementary to experimental lidar data are used to calculate the solutions of lidar equation that fits, in an iterative manner, to the output of the model. Two type of uncertainties are diminished in this way: first, the modeled profiles of lidar ratio are used in lidar data processing instead of a constant value; second, aerosol height profiles are no longer being assumed in the model, but directly measured. This procedure was applied to synthetic lidar signals in order to test its advantages and limitation.

AGLITE is a multiwavelength lidar developed for Agricultural Research Service of the United States Department of Agriculture and its program on particle emissions from animal production facilities. The lidar transmission system is a pulsed Nd:YAG laser (355, 532, 1064 nm) operating at a pulse rate of 10 kHz. We analyze and model lidar backscatter and extinction coefficients to extract aerosol physical properties. All wavelength channels operate simultaneously, day or night, using photon counting and high speed data acquisition. The lidar housing is a transportable trailer suitable for all-weather operation at any accessible site. We direct the laser and telescope field of views to targets of interest in both azimuth and elevation. Arrays of particle samplers and turbulence detectors were also used by colleagues specializing in those fields and are compared with the lidar data. The value of multiwavelength, eyesafe lidars for agricultural aerosol measurements has been confirmed by the successful operation of AGLITE. In this paper, we demonstrate the ability of the lidar system to quantitatively characterize particulate emissions as mass concentration fields applicable for USEPA regulations. The combination of lidar with point characterization information allows the development of 3-D distributions of standard USEPA mass concentration fractions (PM10, PM2.5, and other interesting groupings such as PM10-PM2.5 and PM1). Lidar measurements are also focused on air motion as seen by long duration scans of the farm region. We demonstrate the ability to use "standoff" lidar methods to determine the movement and concentrations of emissions over an entire agricultural facility.

During the summer 2006 an extended observational campaign of atmospheric aerosol has been developed in the area of Granada, South-eastern Spain. From July to the end of September two Cimel CE-318 radiometers have been operated continuously, one at Andalusian Centre for Environmental Studies (CEAMA), located in the urban area of Granada, a non-industrialized medium size city (37.16ºN, 3.61ºW and 680 m a.m.s.l.), and the second one at the Astronomical Observatory of Sierra Nevada (37.06ºN, 3.38ºW and 2896 m a.m.s.l.), with a short horizontal separation between stations that allows us to consider both instrument located in approximately the same vertical column. The Cimel CE-318 measurements have been used to retrieve the aerosol columnar properties, including the columnar volume size distribution, volume scattering phase function, asymmetry factor and single scattering albedo, by means of appropriate inversion procedures. Additionally, at the CEAMA a Raman Lidar system based on a Nd:YAG laser source operating at 1064, 532 and 355 nm and including elastic, polarized and Raman shifted detection has been used to derive profiles of several atmospheric aerosol properties. In this paper we present analyses of the changes and temporal evolution detected in atmospheric aerosol vertical profile. Several long range transport episodes have been detected and back-trajectories analyses and synoptic information have been used in the discussion of results.

One of the main issues of atmospheric research and air quality control is the reduction of harmful particulate matter (PM) in the atmosphere. Small particles can enter the human airways and cause serious health problems such as COPD (Chronic Obstructive Pulmonary Disease), asthma or even lung cancer. Recently, interest has shifted from PM10 to finer fractions of particulate matter, e.g. PM2.5, because the health impact of finer particles is considered to be more severe. Up to now measurements of particulate matter were carried out mainly at ground level. However important atmospheric processes, i.e. particle formation, transport and vertical mixing processes, take place predominantly at higher altitudes in the planetary boundary layer. Lidar in principle provides the ability to observe these processes where they occur. The new method outlined in this paper demonstrates the use of a small sized and quite inexpensive lidar in stand-alone operation to investigate transport processes of particulate matter, and PM2.5 in particular. Continuous measurements of PM2.5 as a reference are gained with a conventional in-situ monitor, installed on a tower at an altitude of 325 m in the North of Berlin (Frohnauer Turm). These PM2.5 measurements will be compared with backscatter Lidar data (1064 nm) taken from approx. 60 m over ground up to an altitude of 15 km with a spatial resolution of 15 m. The vertical backscatter profiles at 325 m will be correlated to the concentrations obtained by the PM2,5 monitor on the tower. Both measurements have a time resolution of 180 s to observe also processes that take place at short time scales. The objective is to gain correlation functions for estimating PM2.5 concentrations from backscatter Lidar data. Such a calibrated Lidar system is a valuable instrument for environmental agencies and atmospheric research groups to observe and investigate causes of high level PM concentrations. First results show a reasonably good linear correlation depending on the level of the relative humidity.

An old-fashioned technology such as the "searchlight profiler", which was used in the 1960s for the early profiling of atmospheric backscatter, recently modified for its use with lasers and CCD cams1, has been revisited in the telemetric-LIDAR described here. The instrument is intended for the low-cost monitoring of urban aerosols, with a limited useful range of 100-200 meters. A modulated CW laser beam is used to probe the atmosphere, and a refractive telescope is used to collect the backscattered light on a photodiode array. Like in a telemetric system, the distance between the laser beam and the telescope axis determines the range resolution and the distance of the measurement volume corresponding to each pixel of the array. The system was used in conjunction with in-situ PM10 instruments for several months of continuous operation in Prato and Florence (Italy). The comparison between LIDAR-derived and conventional PM10 measurements is shown.

A Multiple-Field-Of-View (MFOV) lidar is used to characterize the size and concentration of low concentration of bioaerosol particles. The concept relies on the measurement of the forward scattered light by using the background aerosols at various distances at the back of the sub-visible cloud. It also relies on the subtraction of the background aerosol forward scattering contribution and on the partial attenuation of the first order backscattering. We demonstrate theoretically and experimentally that the MFOV lidar can measure with a good precision the effective diameter of low concentration bioaerosol clouds.

Tropospheric profiles of water vapour and wind were measured with differential absorption lidar (DIAL) and heterodyne detection wind lidar collocated onboard the DLR Falcon research aircraft during the Convective and Orographicallyinduced Precipitation Study (COPS; www.cops2007.de) over Southwest Germany in summer 2007. This international field campaign aimed at refining observational and modelling efforts to improve the forecast skill of convective precipitation over complex terrain in the summer season. The DIAL, a completely new system with four wavelengths (each 50 Hz, 40 mJ) at 935 nm, was installed nadir-viewing. The 2-micron wind lidar was operated either in scanning mode at 20 degrees off-nadir for 3d-wind profiles or in nadir-viewing mode for high resolution vertical wind measurements. The unique combination of both lidars enables the measurement of both horizontal (humidity advection) and vertical (latent heat) fluxes of water vapour that play an eminent role in precipitation forecast and convection initiation. The wind lidar's spatial resolution is 100 m in the vertical and 150 m (vertical wind, boundary layer) to 12 km (3d-wind profiles, whole troposphere) in the horizontal. The DIAL horizontal and vertical resolution ranges from 150 m in the boundary layer to 500 m in the upper troposphere. This high spatial resolution permits the investigation of smallscale processes such as turbulent humidity transport in the convective boundary layer or orographically-induced flow perturbations. Likewise, meso- and synoptic scale processes, e.g. upper level potential vorticity streamers were sampled by flying extended legs across Western Europe.

In this paper, we explore the possibility of determining thenature and variability of urban aerosol hygroscopic properties using multi-wavelength Raman lidar measurements at 355nm, as well as backscatter measurements at 532nm and 1064nm.. The addition of these longer wavelength channels allow us to more accurately validate the homogeneity of the aerosol layer as well as provide additional multiwavelength information that can be used to validate and modify the aerosol models underlying the hygroscopic trends observed in the Raman channel. In support of our hygroscopic measurements, we also discuss our calibration procedures for both the aerosol and water vapor profiles. The calibration algorithm we ultimately use for the water vapor measurements are twilight measurements where water vapor radiosonde data from the OKX station in NYS, are combined with total water vapor obtained from a GPS MET station. These sondes are then time correlated with independent near surface RH measurements to address any bias issues that may occur due to imperfect calibration due to lidar overlap issues and SNR limitations in seeing the water vapor at high altitudes.. In particular, we investigate the possibility of using ratio optical scatter measurments which eliminate the inherent problem of variable particle number and illustrate the sensitivity of different hygroscopic aerosols to these measurements. We find that the use of combine backscatter color ratios between 355 and 1064 together with the conventional extinction to backscatter ratio at 355nm should be able to improve retrieval of hygroscopic properties.

The purpose of this study is to estimate the errors due to several systematic distortions which occur in the procedure of computing water vapor mixing ratio (WVMR) and aerosol scattering ratio (ASR). For WVMR, the systematic distortions are encountered during the following processes: gluing, omission of temperature dependent molecular backscatter coefficient (temperature dependent lidar equation), incomplete overlap correction, and calibration while for ASR during the gluing and omission of temperature dependent molecular backscatter coefficient. The data analyzed are taken with Howard University Raman Lidar (HURL) during WAVES 2006 field campaign. The HURL system operates at the third harmonic of a Nd:YAG laser and acquires data within three channels (354.7 nm, 386.7 nm and 407.5 nm). The study shows the relative errors in computing WVMR and ASR when considering different combinations of the systematic distortions (15 cases for WVMR and 3 cases for ASR) with respect to the case as considered true. The analyses were performed over a time series of WVMR and ASR of about 6 hours and over the altitude range up to 5 km. The range of the relative errors is between ~ 1 % and ~ 18 % for WVMR and between ~ 1 % and ~ 8 % for ASR.

Mounting concern regarding global warming and the increasing carbon dioxide (CO₂) concentration has stimulated interest in the feasibility of measuring CO₂ mixing ratios from space. Precise satellite observations with adequate spatial and temporal resolution would substantially increase our knowledge of the atmospheric CO₂distribution and allow improved modeling of the CO₂ cycle. Current estimates indicate that a measurement precision of better than 1 part per million (1 ppm) will be needed in order to improve estimates of carbon uptake by land and ocean reservoirs. A 1-ppm CO₂ measurement corresponds to approximately 1 in 380 or 0.26% long-term measurement precision. This requirement imposes stringent long-term precision (stability) requirements on the instrument In this paper we discuss methods and techniques to achieve the 1-ppm precision for a space-borne lidar.

In order to better understand the budget of carbon dioxide in the Earth's atmosphere it is necessary to develop a global high precision understanding of the carbon dioxide column. In order to uncover the 'missing sink' that is responsible for the large discrepancies in the budget as we presently understand it calculation has indicated that measurement accuracy on the order of 1 ppm is necessary. Because typical column average CO2 has now reached 380 ppm this represents a precision on the order of .25% for these column measurements. No species has ever been measured from space at such a precision. In recognition of the importance of understanding the CO2 budget in order to evaluate its impact on global warming the National Research Council in its decadal survey report to NASA recommended planning for a laser based total CO2 mapping mission in the near future. The extreme measurement accuracy requirements on this mission places very strong requirements on the laser system used for the measurement. This work presents an analysis of the characteristics necessary in a laser system used to make this measurement. Consideration is given to the temperature dependence, pressure broadening, and pressure shift of the CO2 lines themselves and how these impact the laser system characteristics Several systems for meeting these requirements that are under investigation at various institutions in the US as well as Europe will be discussed.

This paper describes an innovative approach for a new generation of large aperture, deployable telescopes for advanced space LIDAR applications, using the thin active mirror technology. The overall telescope design is presented with a special attention to the optical performances analysis. The mechanical layout with details of the deployment and baffling technique is shown; the complete satellite thermo-elastic analysis mapping the primary mirror deformation due to the thermal loads is presented; the control system architecture is explained and the optical design including the angular and spatial resolution, effective optical aperture and radiometric transmission, optical alignment tolerances, straylight and baffling is deeply discussed. Finally an overview of different mission profiles that this technology can satisfy is presented; the imaging performances can be achieved using the shown technology tuning the surface control to higher performances.

This paper describes the design, manufacturing and test of a ground demonstrator of an innovative technology able to realize lightweight active controlled space-borne telescope mirror. This analysis is particularly devoted to applications for a large aperture space telescope for advanced LIDAR, but it can be used for any lightweight mirror. For a space-borne telescope the mirror weight is a fundamental parameter to be minimized (less than 15 Kg/m2), while maximizing the optical performances (optical quality better than &lgr;/3). In order to guarantee these results, the best selected solution is a thin glass primary mirror coupled to a stiff CFRP (Carbon Fiber Reinforced Plastic) panel with a surface active control system. A preliminary design of this lightweight structure highlighted the critical areas that were deeply analyzed by the ground demonstrator: the 1 mm thick mirror survivability on launch and the actuator functional performances with low power consumption. To preserve the mirror glass the Electrostatic Locking technique was developed and is here described. The active optics technique, already widely used for ground based telescopes, consists of a metrology system (wave front sensor, WFS), a control algorithm and a system of actuators to slightly deform the primary mirror and/or displace the secondary, in a closed-loop control system that applies the computed corrections to the mirror's optical errors via actuators. These actuators types are properly designed and tested in order to guarantee satisfactory performances in terms of stroke, force and power consumption. The realized and tested ground demonstrator is a square CFRP structure with a flat mirror on the upper face and an active actuator beneath it. The test campaign demonstrated the technology feasibility and robustness, supporting the next step toward the large and flat surface with several actuators.

The European Aerosol Research Lidar Network (EARLINET) was established in 2000 to derive a comprehensive, quantitative, and statistically significant data base for the aerosol distribution on the European scale. At present, EARLINET consists of 25 stations: 16 Raman lidar stations, including 8 multi-wavelength Raman lidar stations which are used to retrieve aerosol microphysical properties. EARLINET performs a rigorous quality assurance program for instruments and evaluation algorithms. All stations measure simultaneously on a predefined schedule at three dates per week to obtain unbiased data for climatological studies. Since June 2006 the first backscatter lidar is operational aboard the CALIPSO satellite. EARLINET represents an excellent tool to validate CALIPSO lidar data on a continental scale. Aerosol extinction and lidar ratio measurements provided by the network will be particularly important for that validation. The measurement strategy of EARLINET is as follows: Measurements are performed at all stations within 80 km from the overpasses and additionally at the lidar station which is closest to the actually overpassed site. If a multi-wavelength Raman lidar station is overpassed then also the next closest 3+2 station performs a measurement. Altogether we performed more than 1000 correlative observations for CALIPSO between June 2006 and June 2007. Direct intercomparisons between CALIPSO profiles and attenuated backscatter profiles obtained by EARLINET lidars look very promising. Two measurement examples are used to discuss the potential of multi-wavelength Raman lidar observations for the validation and optimization of the CALIOP Scene Classification Algorithm. Correlative observations with multi-wavelength Raman lidars provide also the data base for a harmonization of the CALIPSO aerosol data and the data collected in future ESA lidar-in-space missions.

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 nm 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 nm 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 km and 2 hours as spatial and temporal distance). First results of comparison between PEARL and CALIPSO observations are shown.

The Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite had been launched in April 2006. Its main goal is to probe the vertical structure and to measure the properties of thin clouds and aerosols plume of the Earth's atmosphere. In order to validate the CALIOP (Cloud-Aerosol Lidar with Orthogonal Polarization) products, correlative measurements between CALIPSO and EARLINET stations have been planned in the framework of the validation campaign. At Napoli EARLINET station correlative measurement have been performed starting from the beginning of June 2006. Results obtained both during daytime with elastic lidar and nighttime with Raman lidar operating at two wavelengths (355nm and 532nm) are shown. The results of the application of a new algorithm to retrieve aerosol basckscattering and extinction coefficient backscattering from space and ground based elastic lidar signals are presented. Case study of Saharan dust outbreaks and cirrus clouds captured during correlative measurement runs are discussed.

The Atmospheric Laser Doppler Instrument (ALADIN) is the payload of the ADM-Aeolus mission, which will provide direct measurements of global wind fields. It will determine the wind velocity component normal to the satellite velocity vector. The instrument is a direct detection Doppler Lidar operating in the UV, which will be the first of its kind in space. ALADIN comprises a high energy laser and a direct detection receiver operating on aerosol and molecular backscatter signals in parallel. The laser is all solid-state, based on Nd-YAG technology and high power laser diodes. The detector is a silicon CCD whose architecture allows on-chip accumulation of the returns, providing photon counting performance. The 1.5 m diameter telescope is lightweight, all made of silicon carbide. ALADIN is now in its final construction stage: the integration of the Flight Model is on-going. Most of the subsystems have been integrated; the payload performance and qualification test campaign will commence. This paper briefly describes the instrument design and provides insights on the development status and the results obtained so far. This regards in particular the receiver performance, the telescope development and the challenges of the laser. The Aeolus satellite is developed for the European Space Agency by EADS Astrium Satellites as prime contractor for the satellite and the instrument.

Due for launch in 2013, EarthCARE (Earth Clouds, Aerosols and Radiation Explorer) has been selected as ESA's sixth Earth Explorer Missions within its Living Planet Programme. Its payload aims at providing measurements, in a radiatively consistent manner, of the global distribution of vertical profiles of clouds and aerosol field characteristics. The EarthCARE payload is composed of four instruments: an Atmospheric backscatter Lidar, a Cloud Profiling Radar, a Multi-Spectral Imager and a Broad Band Radiometer. The EarthCARE mission is a cooperative mission with Japan (JAXA and NiCT), which will provide the Cloud Profiling Radar. ESA will provide the ground segment and the rest of the space segment including the Lidar, the imager and the broadband radiometer. ESA and JAXA have initiated predevelopment activities to reduce technical and programmatic risks for the critical elements of the mission. Following a mission overview, this paper presents results of these pre-development activities mainly related to the ATLID instrument. The activities consist of designing, manufacturing and testing a functional representative model of the ATLID receiver critical units and laser source, of developing and assessing high-power pump laser diodes with extended lifetime and improved efficiency, and of demonstrating the performance of candidate detectors.

In late 2005 the NASA Earth Science Technology Office convened a working group to review decadal-term technology needs for Earth science active optical remote sensing objectives. The outcome from this effort is intended to guide future NASA investments in laser remote sensing technologies. This paper summarizes the working group findings and places them in context with the conclusions of the National Research Council assessment of Earth science needs, completed in 2007.

The SIRTA (Site instrumental de Recherche par Télédétection Atmosphérique) is a ground-based platform located 25km south of Paris in France. The SIRTA observatory was created in 1999 by the French research institute IPSL (Institut Pierre Simon Laplace) to conduct research programs in order to improve the knowledge of radiative and dynamic processes in the atmosphere as well as complex interactions between clouds and aerosols. The objective is to better comprehend climate changes and evolution of environment using a suite a state-of-art active and passive remote sensing instruments. Two ground platforms, a wooden tower, a roof platform and a building (where the lidar operates) are the main facilities of SIRTA. The project team is composed of six persons to ensure the station operations from instrument deployment, maintenance, data transfer and preliminary data analysis. The SIRTA infrastructure enables to conduct many research activities that involve the cloud and aerosol lidar. Some of them will be discussed: the development of the STRAT (Structure of the Atmosphere) algorithm dedicated to automatically discriminate atmospheric layers and retrieve geophysical parameters from lidar profiles, and the CALIPSO validation using the dual-channel backscatter lidar deployed at SIRTA.

An improved methodology for processing scanning lidar data is considered. We demonstrate a new principle of determining vertical profiles of the particulate extinction coefficient and the lidar ratio with the Kano-Hamilton multiangle solution. This technique, which is also applicable to combined elastic/inelastic lidar measurements, computes the extinction coefficient from the backscatter term rather than from optical depth, thus avoiding numerical differentiation. The inversion is based on determining the stepwise column-integrated lidar ratios that provide the best matching of the initial profile of the optical depth to that obtained after the inversion. We explore two approaches concerning the division of the column-integrated lidar ratio into different ranges: in the first case, divisions between ranges are uniformly distributed; in the second case, divisions are located using estimated uncertainty boundaries in the inverted optical depth. The inversion method was used to process the experimental data obtained in the vicinity of large wildfires with the Fire Sciences Laboratory lidar. Examples of the simulated and experimental data are presented, which illustrate the specifics and prospects of this data-processing methodology.

A lidar measurements campaign took in Magurele Platform, southwestern part of Bucharest, during on June 25th, 26th and 28th of 2007 and was intended for aerosol loading characteristics over the urban area. An event of long-range Saharan dust transport to Eastern Europe (Romania) observed during this time is presented in here. We have used an elastic backscattering lidar, based on an Nd:YAG laser, at 1064nm sounding wavelength. It can detect in real time aerosols density profiles up to 10 Km high with a spatial resolution of 12 m. Origin of lidar sampled air masses arriving at various heights over Bucharest have been determined by the analytical back-trajectories from NOAA HYSPLIT model. Saharan dust layers reached the southern part of Romania predominantly by cyclonic circulation due to the strong through observed at all the levels from a cyclonic system located in northwestern part of Africa. Analysis of cloud cover and dust load was estimated by the Dust Regional Atmospheric Modeling (Dream model). The dust event presented highlights how the synergy of Lidar data together with 3-D back trajectories analysis and model calculations can improve our ability to determine accurately the source of high aerosol loading.

Differential Absorption Lidar (DIAL) is a very effective technique for standoff detection of various toxic agents in the atmosphere. The Lidar backscattered signal received usually has poor signal to noise (SNR) ratio. In order to improve the SNR, statistical averaging over a number of laser pulses is employed. The aim of the present work is to select a particular statistical averaging technique, which is most suitable in removing the noise in Lidar return signals. The DIAL system considered here uses laser transmitters based on OPO based (2-5 μm) and TEA CO2 (9-11μm) lasers. Eight commonly used chemical warfare agents including five nerve agents and three blister agents have been considered here as examples of toxic agents. A Graphical User Interface (GUI) software has been developed in LabVIEW to simulate return signals mixed with the expected noise levels. A toxic agent cloud with a given thickness and concentration has been assumed to be detected in the ambient atmospheric conditions at various ranges up to 5 Km. Data for 200 pulses per agent was stored in the computer memory. Various known statistical averaging techniques were used and number concentrations of particular agent have been computed and compared with ideal Lidar return signal values. This exercise was repeated for all the eight agents and based on the results obtained; the most suitable averaging technique has been selected.

At the present time laser systems for atmospheric remote sensing assume the use of powerful pulse lasers in most cases and a signal backscattered from a medium is recorded with a certain step digitization corresponding to the required spatial resolution. Moreover a distance extension of sounding requires essentially disproportionate increase in radiation power and use of complex methods to extend a dynamic range of receiving devices; it also causes the multiple scattering effects which can be difficult to take into account. Qualitatively new approach which allows many by-effects to be avoided is proposed. The approach is based on use of a low-power radiation source (for example, white light) with specified gating, when time of source radiation interruption is equal to a pulse duration of an ordinary lidar (about 10^-8 c), and frequency corresponds to a propagation time of radiation in a zone where the multiple scattering can be neglected. Digitization of the recorded backscattered signal can produce by ordinary digital systems as a discrete readout of signals with the same duration. However to increase a reconstruction accuracy for the medium characteristics we propose to reconstruct the average values of these characteristics over the parts commensurable with the sounding path length. The algorithm proposes creation of recording system with corresponding gating for incoming signal. Estimations have shown that the measurements with accuracy of ~ 1...10 % become possible in the single scattering over the wide range of atmospheric conditions and for safety source power up to 10-20 watt. Moreover, a linear operating mode for photoelectric multiplier can be easily provided and measurements can be carried out in the daytime with the specified accuracy. Such an approach allows us to increase a precision of measurements and can be applied in various areas from the lidar and radar systems to biological and medical devices.

Digital components and architecture offer more flexibility in lieu of analog ones. This asset allows designers to improve electronic equipment and instrumentation behaviour. Lidar processing systems can be improved through new components and architecture, particularly in data collection, acquisition and processing. This paper presents criteria and implementation of an electronic unit capable of substituting Raman lidar - based discriminator and multichannel scaler. For this experiment, a Hamamatsu H7732P-01 photomultiplier has been used.

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.