A mobile multi-channel backscatter lidar for aerosol remote sensing is established at the Meteorological Institute of the University of Munich. The scientific objectives, the instrument concept, and the present state of the data evaluation schemes are briefly described. The potential of the lidar will be demonstrated by several experiments planned for the near future.

At the Dutch National Institute of Public Health and Environmental Protection (RIVM), an automated elastic backscatter lidar at 1064 nm monitors aerosol and low clouds on a routine basis. The lidar data are presently used for several climate-related research issues: (i) the attenuation of solar UV-B irradiance by mixed layer aerosol is assessed by combining the results of a radiative transfer model, measured irradiances from the UV monitoring station of RIVM, and mixed layer heights obtained by lidar. (ii) The lidar forms part of the KNMI Cloud Detection System, which monitors cloud parameters in an area of 120 X 120 km² in a central part of the Netherlands. (iii) Aerosol vertical profile information has been used in a case study at ECN to quanitfy the total radiative forcing by anthropogenic aerosol. At present, a second lidar system, especially designed for cloud detection, is being built in the framework of a new national climate research program in the Netherlands.

We present the first lidar/DIAL system based on a UV-vibronic laser. A self-developed Ce:LiSAF laser was pumped by a quadrupled Nd:YAG and provided high pulse energy (5 mJ at 10 Hz), very high slope efficiency (33%), and a tuning range from 284 nm to 299 nm. The first test results of this frequency-agile Ce:LiSAF based Lidar system are presented here in the form of simultaneous measurements of SO₂ and O₃ concentration profiles. Potentials of other Cerium-doped materials for Lidar applications are discussed.

The means and techniques of lidar sounding are nowadays widely used to obtain the data on the aerosol pollution of the atmosphere, including the industrial emissions and atmospheric characteristics around highways. To add to that scope, pioneering unconventional lidar sounding of optical and microphysical aerosol characteristics was organized during the recent field programs: CLE (Leningrad, 1984), Soviet-American AUTOEX experiment (Leningrad, 1988), Leningrad experiment (1991). The paper presents lidar data obtained from these programs. The problem of interpreting lidar measurements data is discussed. The relationships between optical and microphysical aerosol characteristics are analysed.

The lidar in-space technology experiment (LITE) has been developed at the NASA Langley Research Center to fly on the Space Shuttle and demonstrate the utility of lidar systems in space. An extensive correlative measurements campaign to validate LITE measurements with coincident measurements made with reliable ground-based and balloon-borne sensors was carried out both in Napoli and Potenza in the period September 10-19, 1994. The lidar in Napoli is based on a Xe:F excimer laser (351 nm), while the lidar in Potenza is based on a Nd:YAG laser operating both on the 2nd (532 nm) and 3rd (355 nm) harmonic. During this intense campaign we performed both elastic and Raman measurements for molecular nitrogen. Solar irradiance spectra at ground level were measured by an Optical Spectra Analyzer in the spectral region 0.4-1.1 micrometers , obtaining both columnar water vapor and aerosol load. Aerosol backscattering data will be presented. Elastic and nitrogen Raman signals are used for measuring atmospheric transmissivity. Finally the density and temperature profiles obtained from the simultaneous measurement of the elastic and the N₂ Raman signal will be presented. Simultaneous radiosonde measurements of temperature, pressure, and relative humidity will be used to compare lidar data.

The German Aerospace Establishment (DLR) operates an airborne backscatter lidar based on a Nh:YAG laser which is flashlamp-pumped at 10 Hz. It works on the wavelengths 1064, 532, and 354 nm. It is mounted downward-looking on the research aircraft Falcon 20, flying at about 12 km altitude at speeds of 200 m/s. We present airborne measurements correlated with the orbit tracks of the shuttle-borne LITE-instrument (lidar in-space technology experiment). The emphasis in data evalution is on the comparison between the airborne and the shuttle- borne lidars. First results show excellent agreement between the two instruments even on details of cirrus clouds. The results comprise cloud geometrical and optical depths, as well as profiles of aerosol backscattering coefficients at three wavelengths.

The Optical Science Center North Rhine-Westphalia has developed LIDAR telescopes with mirror diameters of 1150, 1500, and 1800 m. The telescopes are intended for use in the Arctic and must withstand extreme weather conditions. In addition, the parallelism of the transmitted and received beam paths must be maintained under all circumstances. It will be shown how, due to the design principle, these requirements have been fulfilled at moderate cost.

A combined Raman and elastic-backscatter lidar for independent profiling of tropospheric aerosols, moisture, and ozone and aerosol parameters is presented. GKSS operates this advanced Raman lidar at Geesthacht, Germany. First routine ozone measurements were taken between February and April 1995, Simultaneously with the European SESAME (Second European Stratospheric Arctic and Mid-latitude Experiment) campaign. The transmitter contains two lasers, a XeCl excimer laser and a frequency-tripled Nd:YAG laser. The received backscattered light is separated in an eight-cahnnel filter polychromator and detected by photomultipliers in single-photon counting mode. Ozone concentrations and aerosol and moisture profiles are obtained by applying the Raman-DIAL and conventional DIAL and the Raman lidar technique, respectively. Aerosol and moisture profiles and derived by applying the common Raman technique. Examples of the measured aerosol, ozone, moisture, and temperature profiles are shown.

The sensitivity of a CO₂-lidar system using the DAS-technique is based on the smallness of two different errors: the DAS measurement error and the error in the absorption coefficient. The first one is given by the system stability and the influence of the atmosphere on the return signal of the lidar, meanwhile the spectral characteristic of the laser radiation and the accuracy of the measurement set up are responsible for the error in the detection limits. The combination of both errors is responsible for the total measurement accuracy. This is important for the comparison of the measurement results with those of a FTIR-spectrometer. Due to a difference in the measurement principle, the spectrometer offers the advantage of a wide, continuous coverage of the spectrum (2-15 micrometers - depending on the used detector), but the usable range is restricted to a maximum distance of about 500m. This tunable lidar- system however can be used for measurement distances of up to 5 km, but is limited on a nubmer of discrete wavelengths.

We present a computer model for simulation of PRN-cw atmospheric backscatter lidar performances. The program for calculation operates on a PC type computer. The model covers a variety of cases for the lidar platforms: satellite borne (nadir-looking), airborne (both nadir- and zenith-looking) and ground based. The estimation of the lidar response function includes the following inputs: A) ESA/ATLID cloud and aerosol backscatter/extinction model and molecular atmosphere backscatter and extinction model, based on US standard atmosphere. B) Terrain surface function model. C) Different M-sequences modulation formats, sub-system parameters and solar background.

We present a pseudo-random-noise modulation, continuous-wave (PRN-cw) total backscatter lidar based on AlGaAs diode laser. The amplitude PRN modulation is introduced by AOM on the cw laser radiation. The detection makes use of a cooled PMT in photon-counting mode. The PRN waveform generator, the data acquisition system and the data processing are steered by the same PC computer. The connections from the laser to the beam-expander and from the telescope to PMT housing are made with optical fibers. Lidar signals of topographic targets, clouds, and the atmospheric return are presented.

During the last 10 years the DLR container LDA (laser doppler anemometer) was used for many wind related measurements in the atmospheric boundary layer. Based on the experiences on airborne cw-doppler lidar was developed and tested. Wind field measurements in the boundary layer and signal strength studies were performed.

Wind profiles in the atmospheric boundarylayer are a very important parameter also to study atmospheric exchange processes. Alaser Doppler anemometer was designed, constructed and testet. The system consists of the laser Doppler anemometer mounted on a pedestal and controlled by a personal computer. A sine wave fitting computer program is used to get the wind velocities and wind direction for the levels selected. This sophisticated program can distinguish between cloud and aerosol signals and uses also the azimuthal anglevelocity for extracting the direction of the wind. The wind field in the atmospheric baundarylayer is highly variable in spatial and temporal scales. For a few possible applications a more frequent wind sensing is necessary, i.e. - forairports located in low level jet areas, -forchemical plants to get information of the transport of toxic gases from leakages, -for military application (artillery). Only a few techniques can be applied to get the wind field in the boundarylayer. The laser Doppler systems are a candidate. There are a few laser anemometry projects performed during the past years (Woodfield and Vaughan,1983, KOpp et al.,1984). RSRE designed and manufactured with GECa LAser True Airspeed Sensor (LATAS) ,a very compact system in the early 80's. Also RSRE and GEC designed and manufactured a cw-laser Doppler system for DLR in 1981. This system was installed in a container and has been operated at airports, artillery ranges and m a Northsea research platform (Werner et al.,1986). Pulsed systems with larger range capacity are in use at NOAA-Boulder (M.J.Post,1990). This paper summarizes the principle technique, gives the special design of the new compact system and presents test and simulation results. The requirements for the system are a compact design and an automatic or half-automatic operation

This paper focuses on the development of very compact remote sensing systems. Accurate wind sensing plays an important role in aviation. Near term applications include: air data sensors, wind shear detection, and performance measurement. Future applications extend to space, utilizing satellites for sensing global and regional winds. These applications require practical solutions that are ultra-reliable, utilize minimal space, cooling, and power and are easily integrated into the parent system. This paper describes design approaches that can be adapted for use with rapidly advancing coherent and eyesafe semiconductor laser technology. These coherent sources have demonstrated over one watt and are commercially available. Results of hardware development using cw solid state lasers for coherent detection while utilizing internal fiber reflections as the local oscillator signal are presented. Finally, future activities are outlined.

A He-Ne laser based profiler for atmospheric wind measurements across a laser beam is compared to an instrument using incoherent infrared light from a photodiode tranmitter. Both optical crosswind profilers use the scintillation of the light source to measure the average wind across the light path. Several techniques to derive the wind velocity from the normalized time- lagged covariance function of two narrow spaced receivers are tested. Nine conventional wind sensors were placed along a 1 km long test path to get a reference wind distribution for the instruments. The tests performed over a wide variety of different weather situations with low to high wind velocities and different turbulent conditions reveal a good performance of the IR scintillometer.

In this paper experimental and theoretical results on the investigation of the statistical properties of the atmospheric aerosol by the laser sounding method and by means of the acoustic meteostation are presented. Mathematical processing of data allowed to calculate turbulent flows of pulse, heat, and aerosol in the surface air layer. The presence gradient measurements was allowed to define scales for the measurement of velocity, temperature, specific content of aerosol particles and a scale of Monin-Obukhov length, and also to estimate according coefficients of the turbulent exchange for pulse, temperature, and atmospheric aerosol.

The paper proposes the new investigation results as for creation of the contemporary neural sensors functioning in soil, water, and atmosphere. The structures possessed by a polyfunctional ecologic sensor, an optical/chemical nonreacting sensor, a polyfunctional laser sensor and a highly sensitive gravi-inertial sensor. As for the case with intelligent sensors, then the probabilistic small-size neurochips and Langmuir-Blodgett films may be used. This system is robust and it is aimed at the eco-objects which possess the undetermined parameters. The input/output sensor date are analyzed. The dynamic properties inherent in the above- mentioned sensors are ivestigated. The support development results are given.

The dialog package SAGDAM (sounding of atmospheric gases by differential absorption method) is intended for simulation of the potentialities of the DAS method for sounding water vapor and ozone on the vertical and slant directions with ground-based, airborne, and spaceborne lidars. Moreover, the package enables one to model the ground-based, airborne, and spaceborne systems for sounding the integral gas content by a long-path differential absorption method. The spectral range is near UV, visible, and infrared spectral ranges. The program calculates: a) vertical profiles of the absorption coefficients and transmittance of the gas under study and the foreign gases, as well as the transmittance of aerosol and Rayleigh atmosphere; b) spatially resolute error including random error and systematic error. The program enables one to determine the optimal pairs of wavelengths for sounding a gas in the specified altitude range and the minimum-detectable concentration of the gas under study (for the long-path method).

The dialog program LPM (long-path method) is intended for imitative modeling of the concentration gas analysis (H₂O, CO₂, O₃, NH₃, C₂H₄) with the path double-wave gas analyzer, equipped with two tunable CO2-lasers. Modeling is designed for four laser systems using the isotopes of CO₂. While modeling the program provides: 1) the calculation of transmittance for a sounding path at wavelengths 'on-line' and 'off-line'; 2) the calculation of atmospheric signals at wavelengths 'on-line' and 'off-line'; 3) the distortion of a signal with a random number for imitation of measuring noise; 4) the calculation of gas concentration from the inverse problem while imitating the sounding of a single gas; 5) the calculation of concentration of several gases (up to five gases) by using the simultaneous signal processing for several pairs of wavelengths (imitation of sounding of several gases). In addition, the program determines: i) optimal pairs of wavelengths; ii) the gas concentration reconstruction error from the sounding data, including the measuring error and the systematic error.

In this paper we present experimental data of studies of fluctuation spectra of the backscattering coefficient by the synchronous registration of three components of wind velocity, temperature and backscattering coefficient in the local air volume at height equal to 5 meter. Measurements were carried out by means of the acoustic meteostation and with the aerosol laser locator. Obtained results had verified differences between of power auto-spectra of wind velocity fluctuations and backscattering coefficient fluctuations at stable thermal stratification, presumably explained away as the effects of temperature stratification and of convective turbulence. When stratification of the surface layer is stable there appears a 'sub- area of buoyancy' (the Boljiano-Monin spectrum) in fluctuation spectra of the coefficient of backscattering. Assuming that the field of concentration of particles is formed at upper boundary of the boundary layer, and then it without substantial changes it delivers by downgoing flows to the earth surface.

MIRELA has been studied and realized in the framework of a French-American MOU on the stand-off detection of chemical agents. It is able to perform DIAL-DISC measurements in the wavelength range 9 to 11 micrometers , by using a frequency agile CO₂ TEA laser. The MIRELA main advantage is its large dynamic range allowing the simultaneous detection of a light cloud and a hard target or the one of a hard target after propagation through a highly- absorbing medium. The description of MIRELA and the results of the first field tests will be given.

We describe a method to increase the tuning rate of a grating-tuned cw CO₂ laser by using an intra-cavity ZnSe wedge as a tuning element. The wedge is mounted on a galvo element directly in front of the grating which forms one of the cavity mirrors. Its orientation determines the angle of incidence of the laser radiation on the grating, and can be adjusted thorugh the voltage applied to the galvo element. This allows fast, accurate switching between different laser lines at a switching rate of up to 30 Hz. This technique is useful for on-line background absorption correction in trace gas monitoring and for multicomponent analysis of gas samples.

The optical design comprises the photometrical calculation, the modeling of the image formation and the optimization of the optical system. This is also true for lidar and leads to specific aspects in the optical design for lidar. The lidar-equation is corrected for near distances, and it is shown that there is a difference between the photometrical calcuation of lidar systems and conventional optical systems. Moreover, for the image formation with coherent radiation one has to apply the formulas which differ from the conventional formulas for incoherent image formation. The generalized formulas for laser image formation are given. Finally, there are shown optimized lidar optical systems: classical on-axis and off-axis mirror systems and also alternative lens- and lens-mirror-solutions.