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A high-resolution helicopter cable obstacle avoidance LIDAR is designed by the laser parallel scanning method, combined with the 3 × 2 rectangular detector array, which greatly reduces the conventional laser radar in the detection of the cable blind area. By simulating the actual detection state of helicopter through the UAV hanging-off test, the cable at 150 m is clearly detected at the data refresh rate of 2 Hz. Through the range detection test, it is verified that the detection distance of the system for φ20 cable is more than 283 m. [ABSTRACT FROM AUTHOR]

In this paper, taking the tilted and off-axis partially coherent beams as the active detection laser beams, the characteristics of the active detection laser beams reflected back by a cat-eye optical lens in atmospheric turbulence are studied analytically and numerically. The analytical expressions for the centroid position deviation γ, the average intensity, the mean-squared beam width and the far-field divergence angle at the receiver plane are derived. It is found that tilted and off-axis active detection laser beams cannot be reflected back by a cat-eye optical lens in the direction of the source. The absolute deviation $$\left| \gamma \right|$$ decreases as the beam coherence decreases. Therefore, partially coherent beams are more suitable as active detection laser beams than fully coherent ones. In addition, $$\left| \gamma \right|$$ decreases greatly due to the aperture effect, and the influence of turbulence on $$\left| \gamma \right|$$ is not monotonic. On the other hand, the influence of the beam coherence and the atmospheric turbulence on the average intensity, the mean-squared beam width and the far-field divergence angle at the receiver plane is also examined, and some interesting results are obtained. The results obtained in this paper are very useful for applications of the active laser detection. [ABSTRACT FROM AUTHOR]

We characterized the white-light supercontinuum emission by a sub-petawatt laser system in the atmosphere via light detection and ranging measurements. As much as 1 J of supercontinuum is generated in the atmosphere, corresponding to a conversion efficiency of 30 %. This generation occurs at altitudes below 100 m. The high initial beam intensity results in the saturation of the number of self-guided filaments. Therefore, the 'photon bath' surrounding the filaments strongly contributes to the white-light generation. These finding is well reproduced by numerical simulations based on the experimental parameters. [ABSTRACT FROM AUTHOR]

A sensor based on a continuous wave quantum cascade laser, operating near 5.2 μm, in combination with integrated cavity output spectroscopy has been developed for simultaneous measurement of nitric oxide (NO) and carbon dioxide (CO) traces in exhaled air. A detection limit of 0.7 parts-per-billion by volume of NO (acquisition time: 1 s) is achieved. Comparison is made with the standard chemiluminescence NO analyzer and commercial CO breath sampler. The QCL-based sensor is tested on healthy subjects at various exhalation flow rates (15, 50, 100 and 300 ml/s) for both online and offline sampling procedures as well as on asthmatic children (offline sampling). Possibilities for measurements of biogenic NO in vivo, i.e., NO coming from human skin tissue, are also demonstrated. [ABSTRACT FROM AUTHOR]

This paper discusses the relationships among the aerosol extinction coefficient error (AECE), background noise, and distance associated with lidar measurements. The AECE calculation is explained in detail, revealing that the AECE is the product of background noise, range squared, and a relation function. The result of an AECE calculation that uses lidar measurements obtained in Nanjing, China, agrees with a calculation that uses a simulated lidar signal. The AECE equation is verified with lidar measurement data and a simulated lidar signal, indicating the AECE equation is reasonable. [ABSTRACT FROM AUTHOR]

Single-frequency bistability performances from a Tm,Ho:YLF laser with two Fabry-Perot etalons near room temperature is reported. For the first time to our knowledge, the single-frequency bistability at 2.05 μm is displayed in the laser operation with the bistable region width of 0-580 mW and the jump power of 0-78 mW, which can be tuned by regulating the length of the laser resonator. The maximum single frequency output power of 180 mW is obtained at the pump power of 2 W, and the laser frequency can be continuously tuned 1.25 GHz. The single frequency bistability laser can be used in laser lidar systems and all-optical switching systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new active remote sensing methodology, based on laser spectroscopy, to evaluate the content of atmospheric trace gases. Its principle consists in coupling a lidar with optical correlation spectroscopy (OCS-lidar). Our theoretical and numerical studies show that OCS-lidar is a robust measurement methodology allowing trace gases environmental, agricultural, and industrial plants surveys. The novelty of this work is threefold. Firstly, we develop a new formalism to remotely evaluate the target gas concentration from optical correlation spectroscopy. Secondly, an acousto-optical programmable dispersive filter has been used to ensure that the lidar signal be spectrally correlated with the target gas of interest. It avoids using a hazardous gas reference cell, as operated in conventional OCS devices. Moreover, a clever spectral correlation is achieved since the contribution of absorption interfering species can then be minimized. Thirdly, to evaluate the performance of the OCS-lidar methodology, a numerical study of methane greenhouse gas is presented to evidence that atmospheric methane mixing ratios are retrievable over two orders of magnitude, from background level up to 100 ppb, within 100-m range resolution. Evaluation of the accuracy and the detection limit, including statistical and systematic errors assessment, are then objectively presented and discussed. [ABSTRACT FROM AUTHOR]

We present novel frequency tuning methods for broadband mid-infrared spectroscopy that take advantage of the unique frequency sampling properties of our recently developed 'nested dual-cavity doubly resonant optical parametric oscillator' (NesCOPO). These methods, referred to as Vernier frequency sampling, enable mode-hop tuning with an adjustable virtual-cavity intermode spacing. Both frequency resolution and span are widely adjustable and can be tailored to fulfill the requirements either for broadband spectroscopy (>50 cm spectral coverage) at low resolution or for high resolution (<0.01 cm) narrow band spectroscopy. The technique is applied to short-range (10 to 30 m) atmospheric CO measurements at 4.2 µm using integrated path differential absorption LIDAR. [ABSTRACT FROM AUTHOR]

A Micro Pulse Polarization LIDAR (MPPL) has been designed and developed for aerosol and cloud studies at National Physical Laboratory, New Delhi, India (28° 35′ N, 77° 12′E) using a low-energy pico-second pulsed Nd:YAG laser at 532 nm and single PMT detector. This has been used for detecting depolarization characteristics with back-scatter coefficient of atmospheric aerosols and clouds. The back-scattered signals are detected at the emitted wavelength with co-polarization and cross-polarization discrimination with a mirror on stepper motor for aerosols and cloud. Data are obtained by MPPL and are inter-compared with a well-established commercial Leosphere made EZ LIDAR, industry standard at the same site and time, and the results are found to be in good agreement. In the present communication the back-scattered coefficient, aerosols optical depth, depolarization ratio etc. obtained using MPPL & EZ LIDAR are discussed in detail. [ABSTRACT FROM AUTHOR]

Doppler wind lidar (DWL) measurements by the fringe-imaging technique in front of aircrafts at flight speed require rapid processing of backscattered signals. We discuss the measurement principle to derive the 3D wind vector from three line-of-sight (LOS) measurements. Then we simulate realistic fringe patterns of a Fabry-Pérot-interferometer (FPI) on a 2D charge-coupled device (CCD) localized at the focal plane behind it, taking atmospheric and instrument properties like scattering and noise into account. A laser at 355 nm with pulse energies of 70 mJ at 100 Hz repetition rate and a range bin of only 10 m were assumed. This yields count rates of 24 (13) million photons per pulse at 56 (76) m distance and 8.5 km altitude that are distributed on a CCD with up to 960×780 pixels without intensification and therefore generate noisy pixel signals. We present two methods for the precise determination of the radii, i.e., wavelengths of these simulated FPI rings and show that both are suitable for eliminating pixel noise from the output and coping with fringe broadening by Rayleigh scattering. One of them proves to reach the accuracy necessary for LOS velocity measurements. A standard deviation of 2.5 m/s including center determination can be achieved with only 20 images to average. The bias is 7 m/s. For exactly known ring centers, each can be even better than 2 m/s. The methods could also be useful for high-resolution laser spectroscopy. [ABSTRACT FROM AUTHOR]

diode-pumped Q-switched and injection-seeded single-frequency laser, generating tunable laser radiation at 935 nm, is presented. Using Nd:YGG (YGaO) as the active medium, the laser that was developed to serve as a transmitter for water-vapor lidar measurements. The configuration consists of a stable resonator in rod geometry that is injection seeded by a narrowband diode laser and stabilized by the ramp-and-fire technique. Energy scaling was done in a power amplifier in slab geometry. Both oscillator and amplifier crystal were diode pumped at 806 nm. More than 30 mJ pulse energy at 100 Hz repetition rate with a beam propagation factor of M<1.4 and pulse duration of 52 ns in single-frequency mode were generated. To our knowledge this is the first direct generation of 935 nm Q-switched pulses from Nd:YGG suitable for water-vapor measurements. The reported results show great promise of this laser in applications where high efficiency and reduced complexity is indispensable, such as for spaceborne or airborne water-vapor lidar instruments. [ABSTRACT FROM AUTHOR]

diode-pumped, single-frequency laser system emitting at 935 nm has recently been developed to serve as the transmitter for water vapor differential absorption lidar (DIAL) measurements. This laser uses Nd:YGG (YGaO) as the active medium and emits radiation directly at 935 nm without the need of additional frequency conversion processes. The system was diode-pumped at 806 nm and was built up in a master-oscillator-power-amplifier configuration. It generates more than 30 mJ of pulse energy at 100 Hz repetition rate with a beam quality ( M) of better than 1.4. Since water vapor DIAL demands for stringent requirements of the spectral properties those were carefully investigated in the scope of this paper. Single-frequency operation is achieved by injection seeding and active length control of the oscillator cavity. The range of continuously tunable single-frequency radiation extends to ∼0.4 nm centered around 935.31 nm. Values of the spectral purity of >99.996% were determined using long-pass absorption measurements in the atmosphere exceeding the requirements by a large margin. Finally, for the first time water vapor DIAL measurements were performed using a Nd:YGG laser. The reported results show much promise of these directly pumped lasers at 935 nm for future spaceborne but also airborne water vapor lidar systems. [ABSTRACT FROM AUTHOR]

Validation measurement in collaboration with existing lidar sites is a very important part of CALIPSO validation program, lidar site in Hefei is invited to collaborate in the CALIPSO validation program. In this paper, ground-based lidar measurements in Hefei performed in coincidence with CALIPSO overpass are presented, attenuated backscatter profiles at 532 nm and 1064 nm, as well as volume depolarization ratio profile at 532 nm measured by CALIPSO are compared with the ones measured by ground-based lidar. The comparisons indicate that CALIPSO measurements are consistent with the ground-based lidar measurements. However, due to the fact that horizontal distributions of aerosols in the lower troposphere and clouds are in most cases inhomogeneous, there are some differences between two lidar measurements in the boundary layer and clouds. The aerosol layer below the semi-transparent thick cloud can be detected by the 532 nm channel of CALIPSO in daytime. [ABSTRACT FROM AUTHOR]

The temperature profile in the upper ocean mixed layer is of great interest for oceanography, weather forecast and climate studies—especially regarding the strong coupling between the atmosphere and the ocean. A lidar system based on Brillouin-scattering can provide such data over an extended region of the ocean. In this paper we report on studies of an excited-state Faraday anomalous dispersion optical (ESFADOF) edge-filter that, when employed as a receiver in a Brillouin-lidar, will enable range-resolved remote measurements from mobile platforms. We focus on the transmission of such a filter operating on the 5 P3/2→8 D5/2 Rb transition (543.30 nm), and its dependence on the vapor density in the high pump intensity regime. Due to quenching processes such as energy-pooling enhanced by nonlinear radiation trapping, as well as plasma formation, a limit on the lower ESFADOF level number density exists. Beyond this threshold the achievable ESFADOF transmission is limited to a few percent. However, our studies show for the first time measured ESFADOF spectra with steep transmission edges with a transmission change of 15% within a few gigahertz. [ABSTRACT FROM AUTHOR]

Coupling between the atmosphere and the ocean takes place predominantly in the upper ocean mixed layer. Knowledge of the temperature profile in this region is therefore of particular interest. In this paper we report a successful measurement of a temperature distribution in a water tube based on Brillouin scattering with a fiber amplifier as the light source. It represents an important step towards the practical implementation of a lidar system for field use. Such a system could provide cost-effective on-line data over an extended region of the ocean and has potential impact to studies concerning climate, oceanography, weather forecasting and hurricane movements. [ABSTRACT FROM AUTHOR]

We report diode end-pumped continuous-wave Tm:YAlO3 slab lasers with high power and high efficiency. At room temperature, b-cut Tm:YAlO3 slabs with doping concentrations of 1, 4 and 5 at.% pumped by fiber-coupled and fast-axis collimated laser diodes with different wavelengths are compared. Tm:YAlO3 slab lasers of 4 at.% doping concentrations have the highest optical-to-optical efficiency. When pumped with fiber-coupled and fast-axis collimated laser diodes, the maximum output powers are 11 W and 15 W, corresponding to a slope efficiency of 52% and 40%, respectively. [ABSTRACT FROM AUTHOR]

A method involving a closed loop adaptive optic system is investigated as a tool to significantly enhance the collected optical emissions, for remote sensing applications involving ultrafast laser filamentation. The technique combines beam expansion and geometrical focusing, assisted by an adaptive optics system to correct the wavefront aberrations. Targets, such as a gaseous mixture of air and hydrocarbons, solid lead and airborne clouds of contaminated aqueous aerosols, were remotely probed with filaments generated at distances up to 118 m after the focusing beam expander. The integrated backscattered signals collected by the detection system (15–28 m from the filaments) were increased up to a factor of 7, for atmospheric N2 and solid lead, when the wavefronts were corrected by the adaptive optic system. Moreover, an extrapolation based on a simplified version of the LIDAR equation showed that the adaptive optic system improved the detection distance for N2 molecular fluorescence, from 45 m for uncorrected wavefronts to 125 m for corrected. [ABSTRACT FROM AUTHOR]

A high-performance airborne water vapor differential absorption lidar has been developed during the past years. This system uses a four-wavelength/three-absorption line measurement scheme in the 935 nm H2O absorption band to cover the whole troposphere and lower stratosphere simultaneously. Additional high spectral resolution aerosol and depolarization channels allow precise aerosol characterization. This system is intended to demonstrate a future space-borne instrument. For the first time, it realizes an output power of up to 12 W at a high wall-plug efficiency using diode-pumped solid-state lasers and nonlinear conversion techniques. Special attention was given to a rugged optical layout. This paper describes the system layout and technical realization. Key performance parameters are given for the different subsystems. [ABSTRACT FROM AUTHOR]

With the help of the generalized Huygens–Fresnel integral and the ABCD matrix approach a bistatic LIDAR system involving a rough target at a distant location in a turbulent atmosphere is modeled. The system operates by means of an optical beam which has arbitrary spectral composition, and states of coherence and polarization. The rough target is modeled as a combination of a Gaussian mirror and a thin phase screen which induces phase perturbations of the components of the electric field. The analytical form of the cross-spectral density matrix of the returned beam is determined, from which the effect of the rough target on the spectral density (intensity) and polarization of the returned wave is analyzed. [ABSTRACT FROM AUTHOR]

A simple method to produce longer filaments with higher ionization density in air by controlling the diameter of an aperture in the laser beam path is studied via an analysis of the backscattered N2 fluorescence collected by LIDAR. Significant increase in the fluorescence signal (approximately by a factor of five depending on the conditions) and an increased filament length was observed at an optimum diameter. 3D + time stochastic numerical simulations have shown that the optimum aperture size corresponds to the case of multiple filament ‘squeezing’ around the propagation axis forming the regularized elongated structure with higher overall amount of plasma. The optimum range of aperture sizes is the same for the initial transverse perturbation scale variation at least within a factor of three. [ABSTRACT FROM AUTHOR]

Remote filament-induced fluorescence spectroscopy is used to probe a cloud of smoke, produced from burning mosquito coils, located at a distance of 25 m from the laser source and LIDAR detector. CN, CH and C2 molecular fragments were identified in the sample. We demonstrate that temporally gated measurement is an efficient technique to easily suppress spectral contaminations, such as white light and atmospheric N2 fluorescence. [ABSTRACT FROM AUTHOR]

Light detection and ranging (LIDAR) experiments are normally pursued for range resolved atmospheric gas measurements or for analysis of solid target surfaces using fluorescence of laser-induced breakdown spectroscopy. In contrast, we now demonstrate the monitoring of free gas enclosed in pores of materials, subject to impinging laser radiation, employing the photons emerging back to the surface laterally of the injection point after penetrating the medium in heavy multiple scattering processes. The directly reflected light is blocked by a beam stop. The technique presented is a remote version of the newly introduced gas in scattering media absorption spectroscopy (GASMAS) technique, which so far was pursued with the injection optics and the detector in close contact with the sample. Feasibility measurements of LIDAR-GASMAS on oxygen in polystyrene foam were performed at a distance of 6 m. Multiple-scattering induced delays of the order of 50 ns, which corresponds to 15 m optical path length, were observed. First extensions to a range of 60 m are discussed. Remote observation of gas composition anomalies in snow using differential absorption LIDAR (DIAL) may find application in avalanche victim localization or for leak detection in snow-covered natural gas pipelines. Further, the techniques may be even more useful for short-range, non-intrusive GASMAS measurements, e.g., on packed food products. [ABSTRACT FROM AUTHOR]

A method is proposed to aid in the comparison of spaceborne lidar measurements with ground-based lidar measurements. The downward attenuated backscatter is constructed from ground-based lidar data, and then compared to the attenuated backscatter measured by spaceborne lidar. To test the accuracy of the method, sensitivity analysis is performed. This method is applied to compare the measurements between the CALIPSO lidar and ground-based lidar at Hampton University. The comparison results show this method is a feasible and reasonable approach for spaceborne lidar validation. Moreover, it can help to retrieve aerosol optical properties. [ABSTRACT FROM AUTHOR]

CO2, CH4, and N2O are recognised as the most important greenhouse gases, the concentrations of which increase rapidly through human activities. Space-borne integrated path differential absorption lidar allows global observations at day and night over land and water surfaces in all climates. In this study we investigate potential sources of measurement errors and compare them with the scientific requirements. Our simulations reveal that moderate-size instruments in terms of telescope aperture (0.5–1.5 m) and laser average power (0.4–4 W) potentially have a low random error of the greenhouse gas column which is 0.2% for CO2 and 0.4% for CH4 for soundings at 1.6 μm, 0.4% for CO2 at 2.1 μm, 0.6% for CH4 at 2.3 μm, and 0.3% for N2O at 3.9 μm. Coherent detection instruments are generally limited by speckle noise, while direct detection instruments suffer from high detector noise using current technology. The wavelength selection in the vicinity of the absorption line is critical as it controls the height region of highest sensitivity, the temperature cross-sensitivity, and the demands on frequency stability. For CO2, an error budget of 0.08% is derived from our analysis of the sources of systematic errors. Among them, the frequency stability of ± 0.3 MHz for the laser transmitter and spectral purity of 99.9% in conjunction with a narrow-band spectral filter of 1 GHz (FWHM) are identified to be challenging instrument requirements for a direct detection CO2 system operating at 1.6 μm. [ABSTRACT FROM AUTHOR]

An incoherent Doppler wind lidar based on the iodine filter at 532 nm is presented for day and night wind measurements, which was developed by the Key Laboratory of Ocean Remote Sensing of Ministry of Education of China, Ocean University of China. The system operates with a fiber and a narrow-band interference filter to reject daylight. A photon counter is used to improve the detection range. Two iodine filters are used to lock the transmitting laser frequency and to discriminate the Doppler frequency shift, respectively. The method to retrieve the wind profile is described. The detection range of wind profiles (with a 136 m vertical resolution) extends from 100 m to 15 km at night and to 12 km during daytime. The detection range covers the troposphere in the middle and high latitude areas. The comparison experiments between the lidar and radiosonde were performed both during the night and during the day. The standard deviation of the wind direction and speed were 15.5° and 3.1 m/s at night and 15.7° and of 3.2 m/s during the day. This system also has the capability to measure the aerosol backscattering ratio. [ABSTRACT FROM AUTHOR]

The design of a 50 Hz single longitudinal mode, diode-pumped and frequency-tripled Nd:YAG master oscillator power amplifier is described, and the first measurements of output parameters are presented. The laser oscillator is injection-seeded by a tuneable monolithic Nd:YAG ring laser and frequency stabilized by minimising the Q-switch build-up time. The laser system will be an integral part of an airborne instrument demonstrator for a first satellite based Doppler wind lidar to measure vertical profiles of one component of the atmospheric wind vector. This paper focuses on the investigation of the frequency jitter and the linewidth of the laser, which are measured on a pulse-to-pulse basis. For this purpose a compact, high accuracy beat frequency monitoring system has been developed at DLR. By operating the amplifier stage at half the repetition rate (50 Hz) of the oscillator, we could reduce the frequency stability from 10 MHz (rms) to 1.3 MHz (rms) (over a 14 s period). We have determined a mean linewidth of 15 MHz (FWHM) at 1064 nm. These measured laser parameters enable wind velocity measurements in the atmosphere (0–15 km) at an accuracy of 1 to 2 m/s. [ABSTRACT FROM AUTHOR]

Forest fires can be the cause of serious environmental and economic damages. For this reason considerable effort has been directed toward forest protection and fire fighting. The means traditionally used for early fire detection mainly consist in human observers dispersed over forest regions. A significant improvement in early warning capabilities could be obtained by using automatic detection apparatus. In order to early detect small forest fires and minimize false alarms, the use of a lidar system and dial technique will be considered. A first evaluation of the lowest detectable concentration will be estimated by numerical simulation. The theoretical model will also be used to get the capability of the dial system to control wooded areas. Fixing the burning rate for several fuels, the maximum range of detection will be evaluated. Finally results of simulations will be reported. [ABSTRACT FROM AUTHOR]

We demonstrated the feasibility of remote detection and differentiation of some very similar agricultural-activity related bioaerosols, namely barley, corn, and wheat grain dusts, through nonlinear fluorescence of fragments induced by the high-intensity inside filaments of femtosecond laser pulses in air. The signals were detected in Lidar configuration with targets located at 4.7 m away from the detection system. All the species showed identical spectra, namely those from molecular C2 and CN bands, as well as atomic Si, C, Mg, Al, Na, Ca, Mn, Fe, Sr and K lines. These identical spectral bands and lines reveal similar chemical compositions; however, the relative intensities of the spectra are different showing different element abundances from these three bio-targets. The intensity ratios of different elemental lines were used to distinguish these three samples. Good reproducibility was obtained. We expect that this technique could be used at long distance and thus played as a sensor of similar biological hazards for public and defense security. [ABSTRACT FROM AUTHOR]

We present measurements of tropospheric O3, SO2 and aerosol from a volcanic emission event using new multi-wavelength differential absorption lidar (DIAL) techniques that enable us to remove the mutual effects between O3 and SO2 from the raw measurements. The aerosol extinction coefficient is retrieved directly from the lidar return signal at the “off” wavelength and is used to estimate aerosol effects on O3 and SO2measurements. Null error, statistical error, and absorption cross-section error are also analyzed. The O3 and SO2 concentrations at height between 1000 m and 2000 m for a volcanic event on September 10, 2001 were about 20 ppb and 10–35 ppb, respectively, with an error less than 10 ppb. The measured SO2 concentration was much higher than the normal SO2 background value (∼1 ppb) in the troposphere. We also measured O3 concentrations from 13 December 2000 to 06 January 2001 and investigated O3 diurnal variation during a 24-hour period on November 24, 2000. A high O3 concentration of about 250 ppb was observed in late December 2000. [ABSTRACT FROM AUTHOR]

A new subnanosecond pulsed laser-source for mid-infrared (MIR) LIDARbased on difference-frequency generation (DFG) in periodically poled LiNbO3 (PPLN) is developed. An output pulse energy of up to 36 pJ is achieved by amplification of the pump and signal laser. A pulse duration of Δτ=538 ps has been measured using silver thiogallate as a non-linear device for an upconversion cross correlation experiment. The mid-infrared pulse duration corresponds to a spatial resolution of Δs≈8 cm in the LIDAR system. [ABSTRACT FROM AUTHOR]

The fluorescence spectrum of ethanol molecules induced by femtosecond laser pulses has been recorded as the fingerprint of the molecules. It was demonstrated that, if this is combined with a LIDAR technique, the fluorescence from pollutants in the atmosphere could be detected over a long distance. [ABSTRACT FROM AUTHOR]

Aerosol and temperature are important parameters for forecasting the weather. Rotational Raman signals of atmospheric molecules and an elastic signal of the molecule and aerosol give good information about the temperature and aerosol extinction and backscattering coefficients. For a rotational Raman signal, we have designed a new kind of lidar signal receiving system which can sum different rotational quantum numbers from J=2, to 9 and J=11, to 20. This integration signal gives a good signal to noise ratio when compared with the temperature lidar system which use an interference filter for a single quantum number. From this new system, we can obtain the temperature parameter and aerosol scattering coefficient with good signal to noise ratio the (SNR) with a normal laser and a small telescope up to several kilometers. Temperature profiles and aerosol profiles show different shapes in different weather conditions. [ABSTRACT FROM AUTHOR]

We report, for the first time to our knowledge, efficient passive Q-switching of the 1.54-μm laser transition in an Er–Yb-doped crystalline medium. The laser configuration is a compact microchip design that is suitable for a range of practical applications such as range finding and lidar. The slope efficiency of 11.6%, pulse duration of 5–6 ns and average output power of 88 mW are all comparable with standard Er–Yb:glass lasers. [ABSTRACT FROM AUTHOR]

We present a general methodology for evaluating the capabilities of a general lidar system encompassing both backscatter (elastic and Raman lidar) and topographic targets. By introducing a well-defined atmospheric reference medium and by individually examining and decomposing the contributions of lidar system parameters including lidar transmitter power, field of view, receiver noise, atmospheric conditions, and sky background on the signal-to-noise ratio, we obtain a simple dimensionless parameterization of the lidar system. Using this parameterization, numerical simulations are carried out to determine achievable lidar performance including operation range, minimum detectable gas concentration, and so on. [ABSTRACT FROM AUTHOR]

A Monte Carlo-based evaluation of the multiple-scattering influence on ground-based Raman lidar measurements is presented. The lidar returns from cirrus clouds are analyzed in order to evaluate vertical profiles of the extinction and backscattering coefficients. Results show that for the typical cirrus cloud, the presence of the multiple scattering can lead to an underestimation of the extinction coefficient by as large as 200% whereas the backscattering coefficient is almost unaffected for the Raman lidar technique. An algorithm to select one or a set of phase functions which fit to the lidar data is also presented. It is an iterative procedure based on Monte Carlo scattering simulation. By comparison of the experimental value of the lidar ratio, corrected for the multiple scattering influence, and the phase function used in the Monte Carlo simulation, one can determine a suitable phase function. The validity and sensitivity of the algorithm have been demonstrated by applying it to simulated cases. The application to some real cases indicates that our procedure allows for the establishing of a practical scattering model for the cirrus clouds. [ABSTRACT FROM AUTHOR]

Ocean temperature profiles are of great importance in oceanography. For instance, an efficient remote sensing measurement technique of these profiles will facilitate climate studies and improvements in weather forecast. In this paper we describe developments towards a practical implementation of a Brillouin-LIDAR system capable of measuring temperature profiles in the ocean. In particular, we focus on our recent work on fiber amplifiers and a receiver unit based on a Faraday anomalous dispersion optical filter. [ABSTRACT FROM AUTHOR]

Implementation of the pure-rotational Raman (PRR) lidar method for simultaneous measurement of atmospheric temperature, humidity, and aerosol extinction and backscatter coefficients is reported. The isolation of two wavelength domains of the PRR spectrum and the suppression of the elastically scattered light is carried out by a double-grating polychromator. Experiments involving elastic backscatter from dense clouds and a solid target confirm the high level of suppression of the elastic light in the corresponding acquisition channels of the two selected PRR domains. Calibration of the temperature channel was done both by comparison with an experimentally verified atmospheric temperature model profile and by inter-comparison with radiosondes. Night-time temperature profiles with high vertical resolution were obtained up to the lower stratosphere. The PRR temperature profile combined with the water vapor mixing ratio obtained from the ro-vibrational Raman channel is used to estimate the relative humidity. [ABSTRACT FROM AUTHOR]

Differential absorption lidar (DIAL) measurements are usually made on single compounds by alternately switching the wavelength between on and off a resonance line. The selection of more than two wavelengths is a mathematical necessity for simultaneous measurement of multiple species or for resolving interference effects between a compound of interest and a background gas such as water vapour or carbon dioxide. This is especially true in the mid-IR region, where many hydrocarbon compounds have important spectral features. We present a method for remote measurement of gas mixtures in the mid-IR region based on a newly developed fast-switching, frequency-agile optical parametric oscillator lidar transmitter. A multivariate statistical procedure has also been applied for this system, which combines a genetic algorithm for wavelength selection with a partial least squares method for identifying individual compounds from their combined absorption spectrum. A calibration transfer is performed for compounds of interest using reference spectra from an absorption spectra database. Both indoor absorption cell measurements and outdoor remote range resolved measurements of hydrocarbon mixtures were performed to explore the performance of the method. [ABSTRACT FROM AUTHOR]

A new approach to remote sensing of the ocean is proposed. It is based on a combination of Brillouin scattering, incoherent lidar techniques and high-resolution frequency discrimination via gas absorption cells. The results of theoretical and experimental research are given. This approach provides the capability of rapid real-time monitoring of sound-speed or temperature profiles both in the open ocean and in littoral zones with high resolution and high accuracy. [ABSTRACT FROM AUTHOR]

A general methodology for rating both performance and potential of lidar systems used for detection of atmospheric trace constituents including pollutants and gas leaks is developed. By individually examining and decomposing the contribution of both lidar system parameters and atmospheric operating conditions on signal-to-noise-ratio, a generalized figure of merit, V, for lidar quality is introduced and evolved. Computer simulations based on V and atmospheric parameters are carried out to determine achievable lidar performance. A simple design procedure is outlined for determination of lidar instrumentation parameters to ensure the best monitoring efficiency for a given set of initial parameters/requirements, including operation range, minimum detectable gas concentration, and so on. [ABSTRACT FROM AUTHOR]

The effective length of self-induced long (∼100 meters) plasma filaments, generated by intense femtosecond near IR laser pulses in air, was measured remotely using a lidar technique. This technique is based on detecting the backscattered fluorescence signal from nitrogen molecules excited along the intense laser pulse propagation path. This opens up the possibility of measuring remotely long filaments extending over hundreds of meters in the atmosphere. [ABSTRACT FROM AUTHOR]

A deconvolution filtering model of multiple scattering in ground-based single field of view (SFOV) LIDAR returns is described. It is based on time series deconvolution techniques. The contribution of multiply scattered photons in SFOV LI-DAR returns can be numerically modeled by processing LIDAR signals without additional information about aerosol properties and measurement geometry. Deconvolution results are in good agreement with those performed by Monte Carlo calculations, showing that the significance of multiply scattered photons is strongly correlated with aerosol concentration. It is found that, for ground-based LIDAR, the contribution of multiply scattered photons to LIDAR signals is typically below 5% in a clear urban atmosphere, and up to 14% in a very dirty urban atmosphere in Hong Kong during winter seasons. [ABSTRACT FROM AUTHOR]

Aerosols can introduce significant errors in measurements of trace gas concentration profiles with differential absorption lidar (DIAL). Here, a solution to counteract the aerosol effect is introduced, which does not depend on additional measurements and is applicable when absorption at the off-wavelength is not negligible. It is based on a numerical solution of the coupled lidar equations and calculates the trace-gas concentration and the aerosol backscatter ratio simultaneously. Consequently, most of the errors introduced by aerosols to DIAL measurements are inherently corrected and, additionally, the aerosol backscatter profiles at the DIAL wavelengths are obtained. [ABSTRACT FROM AUTHOR]

The efficiencies of direct lidars operating at 355, 532, 1064 and 1540-nm radiation wavelengths for early forest fire detection were compared. For each wavelength, the range for reliable smoke-plume detection was estimated on the basis of a computer simulation plume using a one-dimensional "top-hat" gas dynamic model for the calculation of the backscattering and extinction-coefficient profiles within the plume. The agreement between the predicted signal-to-noise ratio (SNR) and experimental results for 532 and 1064-nm wavelength radiation is good. The decrease of the signal-to-noise ratio with distance is maximum for 355 nm and minimum for 1064 nm. At 1540 nm, the decay of SNR with distance is slightly faster, but the SNR is higher than for other wavelengths, leading to the highest detection efficiency for the same energy of the probing laser pulse. For a burning rate of 2 kg/s and a laser beam divergence of 2.5 mr, the maximum distance for reliable detection varies between 6 and 12 km, depending on the wavelength. [ABSTRACT FROM AUTHOR]

The results of statistical simulation of the spatiotemporal structure of the multiply scattered component of lidar returns by the Monte Carlo method are discussed for the case of monostatic sensing geometry. The spatial characteristics of the region of the medium where occurs the last scattering of photon before arriving at the reciever. This region of the medium is called the instantaneous brightness body of multiply scattered radiation. It is demonstrated that the instantaneous brightness body of multiply scattered radiation that propagates toward the receiver may occupy a large volume that does not necessarily coincide with the region of formation of the singly scattered component. The main factors influencing the spatial and brightness characteristics of this volume source are established. The effect of scattering order on the spatiotemporal structure of lidar returns is analyzed for the case of sensing of aerosol haze and advective and radiative fogs with optical thickness 2 < τ < 8. [ABSTRACT FROM AUTHOR]

A novel airborne all-solid-state DIAL system for water vapour measurements in the upper troposphere and lower stratosphere has been developed at DLR. Its transmitter is based on an injection-seeded KTP optical parametric oscillator (OPO) pumped by the second harmonic of a Q-switched, diode-pumped single-mode Nd:YAG laser at a repetition rate of 100 Hz. The OPO is optimised for operation in the spectral region between 920-950 nm with an average output power of 1.2W and a spectral purity higher than 99%. The latter is controlled on a pulse-by-pulse basis during in-flight operation. The system is also designed to perform simultaneous polarisation-sensitive backscatter measurements at 532 nm and 1064 nm for aerosol detection. For the first time, daytime measurements of two-dimensional water vapour cross sections with high vertical (500-750 m) and horizontal (6-20 km) resolution were performed in the tropopause region. Very low mixing ratios (10-50 ppmv) and strong gradients were observed inside stratospheric intrusions. The sensitivity (1-σ error) of the DIAL in the centre of the stratospheric intrusions ranges from 3% (0.6 ppmv) in the near field to 12% (5 ppmv) in the far field (∼ 4 km). First comparisons with in situ measuring instruments show very good agreement. [ABSTRACT FROM AUTHOR]

A pulsed optical parametric oscillator (OPO) with intracavity sum frequency mixing was developed generating energies of up to 16 mJ in the 281-293 nm wavelength range. Both OPO process and sum frequency mixing are pumped by the harmonics of a single, medium-sized Nd:YAG laser. The system is characterized by a high overall efficiency (∼ 4% conversion from 1064 nm to the UV), a very compact set-up and stable and reliable operation. This system was successfully employed to measure tropospheric ozone using the differential absorption lidar (DIAL) technique and shows much promise as a lidar transmitter in airborne case studies as well as in unattended lidar systems for long-term monitoring. An unattended ozone profiling system could already be successfully realized. [ABSTRACT FROM AUTHOR]

Continuous mapping of an ozone episode in Paris in June 1999 has been performed using a differential absorption lidar system. The 2D ozone concentration vertical maps recorded over 33 h at the Champ de Mars are compiled in a video clip that gives access to local photochemical dynamics with unprecedented precision. The lidar data are compared over the whole period with point monitors located at 0-, 50-, and 300-m altitudes on the Eiffel Tower. Very good agreement is found when spatial resolution, acquisition time, and required concentration accuracy are optimized. Sensitivity to these parameters for successful intercomparison in urban areas is discussed. [ABSTRACT FROM AUTHOR]

Provides information on a study which analyzed the lidar, Light Detection and Ranging technique using nonparametric kernel regression methods. Details on the experimental setup; Statistical model of the study; Results of the study.

The possibility of detecting small forest fires with the help of a simple and cheap lidar operating at 0.532-μm wavelength up to distances of about 6.5 km is demonstrated. The values of the signal-to-noise ratio (SNR) achieved in the experiments are consistent with theoretical estimations obtained by computational modeling of the lidar detection process, including simulation of the smoke-plume shape and of the laser beam–plume interaction. This model was used to assess the potential of the lidar technique for fire surveillance in large forest areas. In particular, the upper limiting range for effective detection (SNR>5) of small localized fires in dry- and clear-weather conditions is estimated at 7–15 km depending on operation mode, burning rate, and observation geometry. [ABSTRACT FROM AUTHOR]