Due for launch in 2008, the Atmospheric Dynamics Mission (ADM-Aeolus) has been selected as ESA's second Earth Explorer Core Missions within its Living Planet Programme. Its payload aims at providing measurements of atmospheric wind profiles with global coverage. The key element of ADM-Aeolus is the Atmospheric LAser Doppler Lidar INstrument (ALADIN), a Direct Detection Doppler Lidar in the ultra-violet spectral region operating on aerosol and molecular backscatter signals in parallel. The ALADIN instrument belongs to a completely new class of active optical earth-observation payloads with limited power requirements and high reliability over a three-year lifetime. It will be the first European Lidar in space. Technological challenges have been addressed in an early stage by a pre-development programme that consisted of designing, manufacturing and testing a functional representative model of the receiver of ALADIN (the Pre-Development Model, PDM), and a breadboard of the transmitter. The pre-development programme has been successfully completed and both receivers and transmitter are being refurbished in an airborne configuration. The ALADIN airborne instrument demonstrator (A2D) will be used for ground and airborne campaigns prior to the launch of the satellite. This paper presents the main characteristics of the airborne instrument and the goals of the campaigns.

The background aerosol conditions and the conditions contaminated with aerosol of antropogenic origin (Arctic haze) were investigated during two Arctic campaigns, the Arctic Study of Tropospheric Aerosols, Clouds and Radiation (ASTAR) in 2004 and Svalbard Experiment (SVALEX) in 2005, respectively. Results obtained by application of the two-stream inversion algorithm to the elastic lidar signals measured on two days representative for each campaign are presented. The calculations were done using signals obtained by the nadir-looking Airborne Mobile Aerosol Lidar (AMALi) probing lower troposphere from the AWI research aircraft Polar 2 overflying the stationary Koldewey Aerosol Raman Lidar (KARL) based at the AWI Koldewey Research Station in Ny Ålesund, Svalbard. The method allowed independent retrieval of extinction and backscatter coefficient profiles and lidar ratio profiles for each of the two days representative for both clean and polluted lower troposphere in Arctic.

Backscatter lidars are useful tools for range determination in various applications, particularly if they provide compact and robust set-ups with suitable light sources, efficient sensors and adequate signal processing. A promising perspective to achieve such requirements is offered by the Pseudo-Random Noise continuous wave (PRN cw) lidar technique, employing cw laser diodes as transmitter. Here the Signal-to-Noise ratio (SNR) of such lidar will be investigated in detail for the following cases: power (amplitude) modulation of the transmitted laser beam and analogue detection by an avalanche photodiode, surface detection. The SNR is calculated numerically, allowing selection of the factors limiting the lidar detection under various environmental conditions. A set of various measurements, obtained with a PRN cw lidar, employing a diode laser in the near IR spectral range and an avalanche photodiode will be presented. The results from the analytical and numerical study are compared with the experimental results. Various applications for the PRN cw lidar will be examined and critical factors influencing its detection performances discussed. Finally an outlook is provided for possible applications of such a lidar in specific atmospheric and surface measurements.

A concept for cooling side-pumped laser crystals, using a thin film of evaporating fluid, was investigated for use on future space-based light detection and ranging (LIDAR) instruments. Analyses of the solid crystal domain show that the thin-film cooling scheme will result in improved thermal management of the lanthanide crystal material investigated. Several candidate flow configurations are presented to produce the desired fluid flow across the crystal surface. One-dimensional, axial flow, two-fluid evaporation models were then solved to characterize the fluid and thermal performance of two of the proposed flow configurations. In addition, an incipience model is presented to determine the film thickness constraints necessary to suppress nucleate boiling. The bulk flow model indicates that excellent thermal management of the crystal, low liquid velocities, and low liquid pressure drops are possible with the two axial flow configurations analyzed. The incipience model indicates that liquid film thickness less than 10 microns may be necessary to ensure the complete absence of vapor bubbles in the liquid flowfield. This result indicates a need to develop three-dimensional fluid models for future studies so that more complex flow geometries may be studied.

The fundamental characteristics of supercontinuum filament formation in condensed media are investigated along with several novel techniques for controlling their normally random distribution pattern. The utilisation of these supercontinuum filaments as light sources in remote sensing experiments is also discussed. In the first experiments a longitudinal imaging technique is used to scan through the filament and generate a plot of the intensity profile. From this profile an accurate measurement for the filament length and waist may be obtained. Using a similar set-up, the remarkably stable phase relationship is demonstrated between neighbouring filaments and the consequent interference pattern recorded. The second investigations present techniques for controlling both the radial distribution of filaments and the distance at which they form on the axis of propagation.

The paper discusses the application of Tm³⁺ and Tm³⁺/Ho³⁺-co-doped tellurium oxide fibres for LIDAR applications. Suitably co-doped tellurium oxide glass offers an excellent opportunity for developing high-power tunable laser compact devices, using both the 800 nm, 980 nm, and 1480 nm pumping schemes. Rare-earth ions have large solubility in tellurite glass, which we aim to exploit for designing Tm³⁺ and Tm³⁺/Ho³⁺ lasers operating in the 1.8μm and 2.9μm ranges. The importance of this wavelength band in characterising atmospheric CO₂ and OH measurements will be explained, using the following transitions in Tm³⁺:³F₄ - ³H₆ (1.8 μm), ³H₄ - ³H₅ (2.3 μm) and in Ho³⁺: ⁵I₇ - ⁵I₈ (2.1 μm) and ⁵I₆ - ⁵I₇ (2.9 μm), all of which can be achieved via the pumping schemes at above wavelengths. The paper discusses the spectroscopic characterisations of bulk glass and their applications in the design of single-mode fibres for laser experiments. For 980 nm pumping scheme, the efficient energy transfer via Yb³⁺-ion co-doping to the respective lasing levels in Tm³⁺ and Ho³⁺ is explained. The results from the steady state fluorescence spectroscopy measurements for the energy transfer analysis are explained for laser design. The paper also explains the fibre pumping scheme and laser experiments in the 1.8 μm and 2.05 μm region.

The impact and potential of a polarization selection technique to reduce sky background noise (BGN) for monostatic elastic backscatter lidar measurements is examined. Taking advantage of naturally occurring polarization patterns in scattered sky light, we devised a polarization discrimination technique in which both the lidar transmitter and receiver track and minimize detected sky background noise while maintaining maximum lidar signal throughput. Lidar elastic backscatter measurements, carried out continuously during daylight hours at 532 nm, with a vertically pointing lidar in an urban atmosphere, show that changes of a factor of 10 in detected sky background noise power can occur between different polarization orientations for large solar zenith angles. This translates to over a factor of three improvement in signal to noise ratios (SNR) over conventional un-polarized schemes, depending on inclination of the lidar axis and the solar angle, with potential corresponding improvements in lidar range for elastic backscatter schemes including Raman and DIAL. The experimental measurements show that the diurnal variations in improved signal to noise ratio, including the impact of relative humidity, are consistent with theoretical estimates employing Radiative Transfer (RT) and using an urban aerosol model based on adjacent and simultaneous CIMEL measurements.

The paper describes the fluorescent lidar created for monitoring of the atmosphere and for estimating the content of fluorescent components of organic aerosol. The lidar operation is based on the use of ultraviolet radiation of harmonics of Nd:YAG solid state laser for exciting the atmospheric fluorescence and the spectral analysis of the atmospheric fluorescence is used in the near ultraviolet and blue spectral range with the resolution of 2 nm. The lidar was found to be efficient for remote analysis of organic aerosol occurring as a result of vegetation emission of secondary metabolites to the atmosphere. Fluorescence spectra processing allows us to select some organic compounds, which molecules contain 7 and more carbon atoms. Taking into account the availability of interconnection between organic aerosol and vegetation, in lidar the second harmonic of Nd:YAG laser is also used for exciting the fluorescence of vegetation covers. In this case the receiving system detects the fluorescence of vegetation in the red spectral range conditioned by the chlorophyll of vegetation. Simultaneous detection of the fluorescence from the atmosphere and from vegetation makes it possible to obtain data on the interaction of the atmosphere and underlying surface covered by vegetation. It has been found that a disruption in the vegetation feeding or the impact of pollutions on vegetation resulted in a sharp increase of the fluorescence intensity of vegetation chlorophyll in the red spectral range and in the simultaneous appearance of organic aerosol in the atmosphere adjacent to vegetation in the region of negative impact.

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.

A mobile scanning lidar facility called RASCAL (Rapid Acquisition SCanning Aerosol Lidar) was involved in a measurement campaign in the interior British Columbia and coastal areas, including the Gulf Islands. RASCAL was part of a tandem of highly specialized vehicles providing mobile measurements using dual-wavelength scanning lidar technology and a sophisticated high temporal resolution chemistry package providing real-time in-situ measurements. The synergistic approach allowed detailed measurements of the complex three-dimensional structure of the atmosphere and coincident detailed chemistry observations of the constituents near the ground. One of the measurement sites, included the town of Golden, B.C., a small town nestled between the Purcell Mountains on the west and the Rocky Mountains on the east. The poor air quality in Golden is attributed to local industrial, residential (wood smoke) and vehicular sources as well as the steep mountains rising on both sides, and the absence of wind. These factors provide a unique airshed for air quality observations which include the complex re-circulation of pollutants due to upslope and downslope flows. In addition the springtime months of March and April provide an opportunity to measure the long-range transport of trans-Pacific pollutants that impact the coastal areas of British Columbia frequently and sometimes even penetrate to the borders of Ontario and Quebec. Lidar measurements near Vancouver, Whistler and Saturna Island show the extent and nature of these trans-Pacific plumes.

A new generation Raman LIDAR system is developed for high spatial (1.5 m) and temporal (1 s) resolution humidity and temperature measurements in the lower atmosphere. A multi-telescope array is used so that a near constant LIDAR signal is obtained from 10 m out to 500 m. The system is operated in the solar blind spectral region and corrected for ozone and aerosol influences. A prism polychromator system allows for the separation of the rotational-vibrational Raman bands of water vapor, nitrogen, and oxygen molecules with 'high spectral purity' with a throughput efficiency of greater than 90 %. This LIDAR system will ultimately be used to study the structure of the lower atmosphere over complex terrain and in particular advance our understanding of turbulent blending mechanisms in the unstable atmosphere.

During a measuring campaign in Lindenberg/Germany (14.5°E, 52.5°N) in August 2003, we observed an extended aerosol layer in the upper troposphere with our mobile Aerosol Raman Lidar (MARL). Backward trajectories indicated that this was a plume originating from forest fires. Water vapor Raman measurements performed with the same lidar showed a large discrepancy with co-located radiosonde measurements, which were not observed in undisturbed conditions. We interpret the unexpected properties of these aerosols as fluorescence induced by the laser beam at organic components of the aerosol particles. The detection of fluorescence from ambient aerosol with lidar systems has not yet been reported before. However, organic compounds such as polycyclic aromatic hydrocarbons sticking to the aerosol particles, or bioaerosol such as bacteria, spores or pollen fluoresce when excited with UV-radiation in a way that is detectable by our lidar system. Therefore, we conclude that fluorescence from organic material released by biomass burning induces inelastic backscatter signals which could be observed with the lidar. It provides for a new method to characterize atmospheric aerosols and should be taken into account when performing water vapor measurements with a Raman lidar.

As part of its activities to prepare for a long-term program in Earth Observation, the European Space Agency is carrying out studies with the objective to provide a background for and pave the way towards the definition of a spaceborne lidar system to monitor greenhouse gases and also atmospheric pressure and temperature. The Agency has initiated system and instrument studies to assess the potential to overcome the principle limitations of the existing passive sounding concepts by a Laser based instrument measuring the CO2 column/profile and extending the range of applications to the monitoring of greenhouse gases as CH4, N2O, ozone and also pressure and temperature profiles. The performance assessment results of such sensors and preliminary instrument concepts are discussed in this paper

We have developed and demonstrated both Ytterbium-doped and Erbium-doped, diode-pumped and seeded, fiber amplifiers at 1064 and 1570 nm, respectively. By pulse pumping a one-stage Erbium amplifier, we have shown greater than 20 W peak output power and high wall-plug efficiency. Our pulse-pumping approach improves energy efficiency up to 80% (at 1 kHz PRF) over the identical CW pumping scheme while suppressing amplified spontaneous emission (ASE). We report on the development of these rare-earth doped fiber amplifiers and the application of multi-stage fiber amplifiers to create a multi-spectral laser transmitter ideally suited for space and planetary lidar investigations.

The Laboratory of Science of Climate and Environment (CEA/ CNRS) and LEOSPHERE Company have jointly developed an eye safe, rugged and unattended high resolution scanning lidar ("easy lidar", www.lidar.fr). This system has been used in the frame of the POVA program and has been used in a compact version during the LISAIR (LIdar to Survey the AIR) program in May 2005 in the Paris city, France. The mobile lidar has been used to follow aerosol particles in highways subject to heavy traffic. High spatial and temporal resolution data on the entire planetary boundary layer (1.5 m and 1s respectively) allowed to monitor for aerosol load variability on board a moving car and also to detect for local sources. We observed the doubling of the optical thickness in the morning when traffic is high in the city ring. We also have shown local effect of waste burning plants and train stations. This new type of eye safe lidar will allow to monitor continuously the entire area of a town and suburbs, in order to detect main sources of pollution (transport, traffic jams, industrial plants, natural dust), follow in real time the evolution of the PBL height and provide an estimation of the mass concentration of the aerosol in the PBL.

A new horizontal eye-safe lidar system has been developed for long-term monitoring of aerosol distribution over an urban area in Macao. The lidar system using a 532 nm micro-pulse laser is made eye-safe by expanding the beam diameter to 70 mm. The detector used is a fast photon counting photomultiplier tube with a narrow bandwidth interference filter to cut down the sky background. This system is the first lidar system operated in Macao to study the local aerosol distribution. We will discuss the method of data acquisition and inversion algorithm in this paper. Recent results from such a new lidar system together with some high pollution episodes will be presented. Developments and the possibility of using this lidar for CALIPSO ground validation will also be discussed.

Ozone and aerosol vertical distribution and their time evolution were measured with a combined UV DIAL / 532-nm elastic lidar during the MCMA 2003 field campaign held in April-May 2003 in Mexico City Metropolitan Area (MCMA). The DIAL transmitter is based on a N₂ Raman converter, pumped by the IV^th harmonic of a Nd:YAG laser. The residual second harmonic radiation from the laser is used for aerosol measurements. In the DIAL part of the receiver a dual-telescope configuration ("Long" and "Short" range) is employed to reduce the dynamic range of the signals and a single 20 cm F/4 Newtonian type telescope is used for the aerosol observations at 532 nm. The DIAL wavelengths are transmitted coaxially to the long range telescope and the 532 nm beam is transmitted coaxially to the "aerosol" telescope. The DIAL receiver is equipped with a grating polychromator for spectral separation and the 532 nm receiver uses a narrowband (0.4 nm) interference filter. "Hamamatsu" 5783-06 photosensor modules detect all signals. Ozone concentration was measured to altitudes of up to 6 km AGL and aerosol to 14 km AGL. The height of the PBL was estimated from the aerosol measurements. The diurnal evolution of the PBL and ozone were studied during the campaign. Formation of a residual layer containing elevated ozone concentrations at nighttime, as well as detachment of the PBL in the late afternoon hours were observed.

Recently, the Romanian lidar group implemented a routine monitoring scheme over Bucharest for the observation of aerosol optical properties in the troposphere. The measurements are provided twice per week at specific times (at 9:00 UT and 13:00 UT) for at least 2 hours per observation time. The purpose is to establish a quantitative comprehensive database of both horizontal and vertical distribution of aerosol over Bucharest and surrounding industrial areas, using a Nd:YAG laser based lidar system, operating at 1064 and 532 nm wavelengths, which provides in real time aerosol profiles up to 10 Km high, with a 6 m spatial resolution. In this paper, a statistical analysis obtained from several months of regular measurements is presented, ordinary and special events being outlined. For further analysis, the integration in atmospheric transport models of aerosol's spatial and temporal distribution derived from lidar measurements and complementary meteorological data was pursued. The novelty of this technique consists in using the OpenGIS technology (Open Geographical Information Systems), which permits the visualization and complex analysis of pollution in natural environment: numerical model of terrain, vegetation, meteorological and atmospheric characteristics. Lidar data are integrated as location type, direction and sense, as from the view-point of their temporal distribution. The position information is processed through an azimuthal projection GIS data server, considering the radial distribution of data centered to the coordinate point of installation location. Several codes were modified in order to obtain forecast aerosols trajectories and to evidence the impact on nearby regions.

Micro-Pulse Lidar (MPL) systems have been utilized in a wide variety of field campaigns and are currently deployed at multiple sites around the globe to monitor atmospheric aerosols and clouds on a continuous, multi-year basis. These systems contain a commercial-grade telescope that changes focal-length as a function of instrument temperature resulting in a bias error for retrieved lidar profiles. An analytical model is described that predicts the expected thermal-induced signal response, and is used to correct MPL atmospheric data. Results demonstrate a significant reduction in data bias error.

Aerosols are among the most spatially variable components of the atmosphere, and thus their study requires their monitoring over a broad geographic range. The backscattering of light from suspended solid and liquid particles in the atmosphere obeys Mie scattering theory. Light attenuation in the spectral region from 300 to 4000 nm due to Mie scattering exceeds that due to molecular (Rayleigh) scattering and ozone absorption combined. This occurs despite the fact that aerosol particle concentrations in the atmosphere are many orders of magnitude smaller than molecular concentrations. Starting from the characteristics of urban aerosols measured over the city of Cali (Colombia), 3° 30' N, 76° 30' W, with a PM10 particle selector, along with information on meteorological conditions typical of the region, we present the results of a study of light scattering properties generated using a model applied Mie scattering theory to size parameter between 0 and 50, with an increment of 0.01, and Matlab computer code, to simulate and predict measurements with a Lidar system operating at 532 nm.