The U.S. Air Force seeks reliable wind measurements in the vicinity of clouds from the perspective of a satellite platform or high altitude aircraft. These wind observations may be used as input to tactical decision aids or assimilated into weather forecast models. There is also interest in making direct wind measurements below clouds by sampling through optically thin gaps. Ground-based and airborne-based lidars have demonstrated the ability to make direct measurements of horizontal winds based on determination of the wind-induced Doppler shift in the backscatter signal. To develop an optimal design concept for space-based lidar platforms, a simulation model has been developed to address questions of optimum laser wavelength, pulse length, minimum power, scanning strategies, optimal signal processing and wind computation algorithms. This paper presents an operational simulation model, the Defense Lidar Simulation Model (DLSM), for space- based/airborne coherent and incoherent Doppler lidar wind sounders that produces simulated Doppler lidar winds using either global or mesoscale atomospheric model wind fields.

We present a holographic Raman lidar system, which can provide temperature profiles of the atmosphere. The Raman lidar has the potential to operate continuously over a 24 hr period, with a predicted accuracy of 1% at altitudes greater than 20 km. The distinguishing feature of our lidar that allows 24 hr measurements is the holographic optical element. The holographic optical element can resolve individual rotational Raman lines at high efficiency. Furthermore, this high resolution substantially increases the signal to noise of the lidar system, thereby allowing daytime measurements with out appreciable increase in error.

Raman lidar techniques have been demonstrated which provide most valuable descriptions of the evolution of air pollution events. The vibrational and rotational Raman lidar signals provide simultaneous profiles of meteorological data, ozone and measurements of airborne particulate matter. An operational prototype Raman lidar instrument was prepared and demonstrated for the US Navy and is now used for scientific investigations. It makes use of second and fourth harmonic generated laser beams of a Nd:YAG laser to provide both daytime and nighttime measurements. The Raman scatter signals from vibrational states of water vapor and nitrogen provide robust profiles of the specific humidity in the lower atmosphere. The temperature profiles are measured using the ratio of rotational Raman signals at 530 and 528 nm from the 532 nm (second harmonic) beam of the Nd:YAG laser. In addition, the optical extinction profiles are determined from the measured gradients in each of several molecular profiles compared to the molecular scale height. We currently use the wavelengths at 284 nm (nitrogen vibrational Raman), 530 nm (rotational Raman) and 607 nm (nitrogen vibrational Raman) to determine profiles of optical extinction. The ozone profiles in the lower troposphere are measured using a DIAL analysis of the ratio of the vibrational Raman signals for nitrogen (284 nm) and oxygen (278 nm), which are on the steep side of the Hartley band of ozone. Several data sets have been obtained during air pollution events and the results from these events have been the subject of recent studies. The examples presented in this paper have been selected to show the new level of understanding of air pollution events that is being gained from applications of lidar techniques.

The carried out experimental measurements of structures of speed and the directions of a wind with the help created meteorological lidar MEL-01 have confirmed perspective of its use for sounding of bottom troposphere. The results of numerical modeling of sounding of the atmospheric temperature and humidity profiles by differential absorption method in the near IR spectral range by means of the MEL-01 meteorological lidar show that the three-frequency method using the absorption lines from the band 0.72 in tropics and mid-latitude summer can compete with the two-frequency method of separate sounding of temperature and humidity. Only the two-frequency method is practical in the Arctic winter conditions. The absorption band of 0.94 is only weakly suitable for sounding in the atmospheric boundary layer.

In this study laser scanner canopy height metrics data from the laser scanner Toposys-1 were investigated to derive forest attributes such as timber volume, tree height, and crown area coverage for the use in forest inventories. Investigations were based both on single tree information from crown segmentation and stand-wise assessments. while the statistical stand-wise approach only utilizes mean values for stand areas, the single tree classification approach makes use of the full potential of the high resolution laser scanner data. Forest inventory parameters were classified on the base of single trees or small groups of trees using digital image processing methods such as segmentation and data filtering. Stand-wise forest inventory data and single tree information were regressed against laser-derived features. Accuracy for additional stand parameters depends on crown closure and tree species. The obtained accuracy for tree heights from the approaches described is within the accuracy of conventional field based measurements. Further, it was investigated in how far laser scanner data is appropriate to assess timber volume. The described approaches can be used operationally for stand- wise forest inventories. Especially the single tree approach can be used instead of time- and cost-intensive field work in cases when full enumeration is required.

One of the limits to the sensitivity of differential absorption lidar (DIAL) when using a topographic reflector is the spectral variation of the reflectance of the topography (differential albedo). This is especially a problem when DIAL is attempted from a mobile platform that views changing background scenes. Recent advances in technology allow one to generate laser radiation that is tunable over broad spectral ranges. We show that the differential albedo problem can be largely corrected by judicious selection of a set of at least three lidar wavelengths to detect and measure each single species of interest. We show that the degree of correction which can be obtained depends on the joint spectral properties of the reflectance of the background and of the species absorption coefficient. We show that use of a simple polynomial model for the background reflectance provides detection sensitivities at the part per million-meter level for hydrocarbon species in the 3 micron region. We propose that the multi-wavelength technique can also be used to determine changes in background absorption when that background absorption is not small.

This paper focuses on an adaptive multi-resolutional algorithm for generating forest floor digital elevation models by processing the three dimensional data acquired by the laser scanner. The adaptivity of our algorithm ensures that it can be used successfully in flat, hilly, and mountainous terrain and deliver accurate results. A large set of GPS ground reference points are used to verify the algorithm along with others commonly used. First results show that the average error is between 0,5 and 1m for an Alpine region in Austria which is very close to the error the laser scanner data distributor claims for flat terrain. This study is part of the HIGH-SCAN project (EU IV Framework/Center of Earth Observation), a project whose objective is to provide methods to integrate high satellite imagery and laser scanner data for forest inventory.

High-pulse-rate laser scanners are capable to detect single trees in boreal forest zone, since significant amount of laser pulses reflect directly from the ground without any interaction with the canopy. This allows detailed investigation of forest areas and the creation of a 3- dimensional tree height model. By extracting the height, location and crown dimension of the trees from the 3- dimensional tree height model and by using the tree species information available in aerial photographs and in laser scanner data, important tree attributes, such as stem volume, basal area, and age, can be estimated for single trees. By knowing the characteristics of single trees, forest characteristics for sample plots, stands and larger areas, such as stem volume per hectare [m³/ha], basal area per hectare [m²/ha], mean height, dominant height, mean age, number of stems [pc/ha] and development class, can be calculated. The advantage of the method is the capability to measure physical dimensions from the trees directly and the capability to use existing conversion formulas for stand attributes. This paper describes the methods and gives a first indication of the performance of the developed method. It is shown that tree heights of individual trees in the dominating storey can be obtained with less than 1 m standard error. In addition, the following standard errors were obtained for mean height, basal area and stem volume at stand level: 2.3 m (13.6%), 1.9 m²/ha (9.6%), and 16.5 m³/ha (9.5%), respectively, even without using the tree species information. The accuracy was better than the accuracy of conventional standwise field inventory. It was also demonstrated that laser scanner is significantly more accurate than imaging spectrometer AISA in the stand attributes retrieval.

This paper evaluates and discuses the accuracy of laser scanner in DTM (digital terrain model) generation in forested and suburban areas. Special emphasis is laid in order to optimize the selection of ground hits used for the creation of the DTM of future high-pulse-rate laser scanners. A novel DTM algorithm is depicted in detail. The algorithm is based on five phases: (1) calculation of the original reference surface, (2) classification of vegetation and removal of the vegetation from the reference surface, (3) classification of the original cloud of points using the reference surface, (4) calculation of the DTM based on the classified ground hits, and (5) interpolation of the missing points. Standard error of 15 cm was obtained for flat forest areas and the error increased with increasing terrain slope to the value of approximately 40 cm at the slope of 40%. The average standard error for forest area was slightly better than 25 cm. The laser-derived DTM of the forest road deviated only 8.5 cm from the true height. An optimum performance for the DTM generation was obtained by averaging the ground hits which located, at the maximum, 60 cm above the minimum terrain values. A simplified algorithm was suggested for more operational use based on the first pulse mode data. Special cases of the suburban area DTM were verified including terrain heights below the buildings and bridges, terrain heights of roads, terrain heights below large outdoor light fixture, to name but a few. About 100 special cases in suburban/urban environment for DTM verification were searched. The corresponding standard error between the laser-derived values and reference data was 45 cm.

On February 14, 2000, after a 4-year transit, the recently renamed Near-Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft entered a 300-km orbit around the asteroid 433 Eros. Onboard the spacecraft, the NEAR Laser Rangefinder facility instrument began operation providing high-resolution topographical profiles of Eros. Developed at the Johns Hopkins University Applied Physics Laboratory, the NLR is a bistatic, direct-detection laser altimeter. The transmitter uses a gallium arsenide diode-pumped Cr:Nd:YAG laser at 1.064 micrometer. This lithium-niobate Q-switched transmitter emits 15-ns pulses at 15.3 mJ/pulse (1/8 to 8 Hz), permitting reliable NLR operation at the required 50-km altitude. The separate receiver employs an extended infrared-sensitive avalanche-photodiode detector with a 7.62-cm clear aperture Dall-Kirkham collecting telescope. End-to-end calibration capability exists between the transmitter and receiver via a 109.5-m spooled fiber-optic. A fraction of each emitted outgoing laser pulse is sampled, optically delayed and injected into the receiver optics providing a 'fixed target' to the NLR. In preparation for sampling Eros, the NLR has been operated numerous times during the 4-year transit period. These 'post-launch tests' provided housekeeping and calibration data useful in characterization and verification of the NLR design. This article summarizes the design used, post-launch test results, and implementation details used to control the NLR illustrating the complexity of operating an instrument in deep space. Additionally, preliminary evaluation of NLR performance using preliminary altimetry data of 433 Eros is presented.

The comparative research of the chlorophyll contents for number of wood plants by traditional spectrophotometric and fluorescent laser methods is carried out.The seasonal changes of the chlorophyll sums in the sprint-summer period at coniferous and deciduous wood plants are analyzed. The supervision over changes in the chlorophyll contents in connection with a withering of needles and leafs are carried out. The experimental results are received by spectrophotometric and lidar methods of study of a course of chlorophyll seasonal dynamics and pigment complex destruction of during a withering of needles and leafs of wood plants. The results of the joint analysis have shown identity of results received essentially by various methods.

The U.S. Army Research Laboratory (ARL) is currently investigating unique self-mixing detectors for ladar systems. These detectors have the ability to internally detect and down-convert light signals that are amplitude modulated at ultra-high frequencies (UHF). ARL is also investigating a ladar architecture based on FM/cw radar principles, whereby the range information is contained in the low-frequency mixing product derived by mixing a reference UHF chirp with a detected, time-delayed UHF chirp. When inserted into the ARL FM/cw ladar architecture, the self-mixing detector eliminates the need for wide band transimpedance amplifiers in the ladar receiver because the UHF mixing is done internal to the detector, thereby reducing both the cost and complexity of the system and enhancing its range capability. This fits well with ARL's goal of developing low-cost, high-speed line array ladars for submunition applications and extremely low-cost, single pixel ladars for ranging applications. Several candidate detectors have been investigated for this application, with metal-semiconductor-metal (MSM) detectors showing the most promise. This paper discusses the requirements for a self-mixing detector, characterization measurements from several candidate detectors and experimental results from their insertion in a laboratory FM/cw ladar.

A novel approach to the measurement of electromagnetic fields is described and demonstrated. The approach is based on the use of a local oscillator which is tuneable in a spatial mode sense. The technique provides a field analysis capability equivalent to that achievable with a phased array receiver but only requires a single aperture and a single detector. The principle behind the concept is described and successfully demonstrated with a hollow multimode waveguide version of the Michelson interferometer, a CO₂ laser source and a thermopile detector. Measurements of the waveguide mode spectra excited by the field returned from a tilted plane mirror target positioned at the exit of the interferometer are shown to be in good agreement with theoretical predictions. The technique has the interesting property that the spatial resolution with which fields can be analyzed is independent of detector dimensions. In suitable technologies the underlying concepts should be applicable across the electromagnetic spectrum.

Previous efforts to develop 3-D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes the progress that has been made in program developing an approach that will enable a complete 3-D ladar image (angle-angle-range) to be captured with a single pulse. It has been previously reported that a unique processor chip was designed and fabricated that was intended to be bump bonded directly behind a detector array, the sensor provides separate independent range finder circuitry for each pixel. The time-of-flight for each pixel is recorded on the chip and the values are then read out serially. This approach allows the range resolution to be determined by the laser pulse width and electronics bandwidth and to be independent of image framing rates. The original version of this concept is a 32 X 32-pixel device. A silicon photo-diode array was bonded to the processor chip. This limited the useful wavelength of the sensor 1 micron and below. Images generated using this sensor will be presented. The effects of shot-to-shot fluctuations, turbulence and scintillation on image quality will be discussed. The next generation, under development at this time, will also be presented. This sensor will be a 64 X 64-pixel device. The detectors will be electron-capture anode plates and the device will be sealed into an image intensifier tube. The photocathode material will be InGaAs, engineered to be sensitive to 1.5 microns. Results from the photocathode development effort, including quantum efficiency and micro-channel plate gain will be presented.

Hyperspectral imaging has demonstrated impressive capabilities in airborne surveys, particularly for mineral and biomass characterizations. Based on this success, it is believed that other applications like search and rescue operations, and detection/identification of various ground military targets could greatly benefit from this technology. The strength of hyperspectral imaging comes from the access to another dimension of information: the spectral content of the detected return signal for each spatial pixel. In the case of conventional hyperspectral imaging, the return signal depicts the spectral reflectance of the day irradiance from the scene within the field of view of each pixel. However, by inserting a range-gated intensifier into a hyperspectral camera and by combining the camera with selected pulsed lasers, it becomes possible to relate the returned spectral information to specific light/matter interactions like induced fluorescence. This new technique may be referred to as 'active hyperspectral imaging.' Among its advantages, this approach is independent of the ambient lighting conditions and can be customized in excitation wavelengths. Moreover, by using a range-gated intensified camera, it is possible to survey limited area with a significant increase in signal-to-noise ratio. A camera of this type has been built by our group in collaboration with private industry and is described in this paper. The internal design of the camera is discussed, new issues concerning the calibration of the camera are depicted and a model based on signal-to-noise ratio analysis is presented. From the fluorescent characteristics of surrogate land mines measured in the laboratory, this model is used to predict the capabilities of detecting surface-laid mines from an aerial platform based scenario.

We describe the technical approach, component development, and test results of a line imager laser radar (ladar) being developed at the Army Research Laboratory (ARL) for smart munition applications. We obtain range information using a frequency modulation/continuous wave (FM/cw) technique implemented by directly amplitude modulating a near-IR diode laser transmitter with a radio frequency (rf) subcarrier that is linearly frequency modulated. The diode's output is collimated and projected to form a line illumination in the downrange image area. The returned signal is focused onto a line array of metal-semiconductor-metal (MSM) detectors where it is detected and mixed with a delayed replica of the laser modulation signal that modulates the responsivity of each detector. The output of each detector is an intermediate frequency (IF) signal (a product of the mixing process) whose frequency is proportional to the target range. This IF signal is continuously sampled over each period of the rf modulation. Following this, a N-channel signal processor based on field- programmable gate arrays (FPGA) calculates the discrete Fourier transform over the IF waveform in each pixel to establish the ranges to all the scatterers and their respective amplitudes. Over the past year, we constructed the fundamental building blocks of this ladar, which include a 3.5-W line illuminator, a wideband linear FM chirp modulator, a N-pixel MSM detector line array, and a N-channel FPGA signal processor. In this paper we report on the development and performance of each building block and the results of system tests conducted in the laboratory.

This paper proposes a new optoelectronic delay locked loop (OE-DLL) and its use in optical ranging systems. The so called PMD-DLL receiver module is based on a novel electro-optical modulator (EOM), called the Photonic Mixer Device (PMD). This sensor element is a semiconductor device, which combines fast optical sensing and mixing of incoherent light signals in one component part by its unique and powerful principle of operation. Integration of some simple additional on-chip components offers a high integrated electro-optical correlation unit. Simulations and experimental results have already impressively verified the operation principle of PMD structures, all realized in CMOS technology so far. Although other technologies are also promising candidates for the PMD realization they should not be further discussed in this contribution. The principle of the new DLL approach is intensively discussed in this paper. Theoretical analysis as well as experimental results of a realized PMD-DLL system are demonstrated and judged. Due to the operation principle of sophisticated PMD devices and their unique features, a correlation process may be realized in order to synchronize a reflected incoherent light wave with an electronic reference signal. The phase shift between both signals represents the distance to an obstacle and may be determined by means of the synchronization process. This new approach, avoiding so far needed critical components such as broadband amplifiers and mixers for the detection of small photo currents in optical distance measurement, offers an extremely fast and precise phase determination in ranging applications based on the time- of-flight (TOF) principle. However, the optical measurement signal may be incoherent -- therefore a laser source is not needed imperatively. The kind of waveform used for the modulation of the light signal is variable and depends on the demands of every specific application. Even if there are plenty other alternatives (e.g., heterodyne techniques), in this contribution only so called quasi-heterodyne techniques - - also known as phase shifting methods -- are discussed and used for the implementation. The light modulation schemes described in this contribution are square-wave as well as pseudo-noise modulation. The latter approach, inspired by the wide spread use in communication as well as in position detection (e.g., IS-95 and GPS), offers essential advantages and is the most promising modulation method for the ranging approach. So called CDMA (code division multiple access) systems form a major task in communication technology investigations since the third generation mobile phone standard is also partly based on this principle. Fast and reliable synchronization in direct sequence spread spectrum communication systems (DSSS) differs hardly from the already mentioned ranging approach and will also be discussed. The possibility to integrate all components in a monolithic PMD based DLL design is also presented and discussed. This method might offer the feature to integrate complete lines or matrixes of PMD based DLLs for highly parallel, multidimensional ranging. Finally, an outlook is given with regard to further optimized PMD front ends. An estimation of the expected characteristics concerning accuracy and speed of the distance measurement is given in conclusion.

In this paper, a digital time of flight laser range finder is presented. This measurement method has been simulated and experimentally evaluated using an eye-safe (class IIIA) laser range finder based on a passively Q-switched microchip laser as emitter and an avalanche photodiode as receiver. This new concept of measurement overcomes instability of classical time of flight laser range finder versus the reflectivity of the target, the atmospheric transmittance and the photoelectric noise. Classical laser range finder uses analog techniques to measure the time elapsed between the start and stop laser pulses: start time and stop time are defined by analog thresholds, therefore accuracy is greatly affected by the SNR in the receiver and associated electronics. This SNR is also dependent on emitter and receiver geometric configuration. Therefore the power seen by the receiver as a function of the distance measurement has been estimated theoretically and observed in experiments in order to optimize SNR over a chosen range. A new technique to overcome this lack of accuracy has been implemented using a fast digitizer with an acquisition rate of 10 GS/s and digital signal processing algorithms. Accuracy of about +/- 5 mm for a single shot without averaging and +/- 0.5 mm for averaging 20 shots have been demonstrated from 10 meters to 250 meters using only one photodetector for the start and stop pulse. Such a system will have an interest in the area of 3D vision laser ranging where there is a need of high accuracy measurements.

Free space optical beam propagation is largely limited by the visibility of the channel at a particular location and at a particular time. In the absence of highly scattering particles, such as rain drops and snow flakes, the scintillation is the most severe limitation to system performance in an optical channel. An area of application mathematically similar to optical communications is laser radar. In a laser radar, a beam is transmitted through a channel, the atmosphere in our case, reflected by a target and received either at the same location it was transmitted from (monostatic channel) or another location (bistatic channel). Knowledge of the scintillation of the reflected beam could not only help design an appropriate receiving system, but could also give information about the reflecting object that could be utilized in forming its optical signature. Using our recently developed theory, we calculate the scintillation of a Gaussian beam propagating through atmospheric turbulence and reflected by a point target. The double pass scintillation is investigated for monostatic and bistatic channels and results are compared with our experimental data collected by an eight aperture heterodyne detection system.

A 3-D laser tracking scanner system analysis focusing on immunity to ambient sunlight and geometrical resolution and accuracy is presented in the context of a space application. The main goal of this development is to provide a robust sensor to assist in the assembly of the Space Station. This 3- D laser scanner system can be used in imagery or in tracking modes, using either time-of-flight (TOF) or triangulation methods for range acquisition. It uses two high-speed galvanometers and a collimated laser beam to address individual targets on an object. In the tracking mode of operation, we will compare the pose estimation and accuracy of the laser scanner using the different methods: triangulation, TOF (resolved targets), and photogrammetry (spatial resection), and show the advantages of combining these different modes of operation to increase the overall performances of the laser system.

Laser radar systems are required for various military applications including obstacle detection, target recognition, and terrain mapping. Each application requires different system parameters such as pulse energy, repetition rate, and field of view. This paper is the second in a series of papers describing the progress toward a multifunction laser radar system under construction for the Cooperative Eyesafe Laser Radar Program (CELRAP) of the U.S. Army CECOM Night Vision and Electronic Sensors Directorate.

This paper describes the development of real-time non-contact metrology based on holographic interferometry and neural network fringe analysis software to detect defects in composite materials. The object under inspection is illuminated by a high-power solid-state laser, and the light scattered from the material surface is recorded in real time using a double-exposure holographic interferometer, which can detect minute surface deformation caused by defects in the material. Thermal stimulation of the object creates a non- uniform time-varying material reaction, which causes surface deformation that is characteristic of the material's internal structure. This deformation in turn creates time-varying interference patterns, which are recorded by a real-time holographic interferometric system and displayed on the computer monitor through a CCD camera. The system allows real- time, in-depth non-contact inspection of composite materials used in aircraft and other military vehicles. A genetic algorithm has also been developed for fast data processing in a non-laboratory environment. The sophisticated neural network recognizes the types of defects at high speed.

Multiple-Slit Streak Tube Imaging Lidar (MS-STIL) represents a new method for using streak tubes in a laser radar configuration. The MS-STIL approach uses several slits instead of the usual single slit to provide a number of additional capabilities over conventional laser radar systems. System configurations for providing 3D single-laser-pulse scannerless imaging, 3D multispectral imaging, 3D multispectral fluorescence imaging, 3D polarimetry, and combined 3D spectro- polarimeters are presented. In addition, a very high-speed laser diagnostic system capable of measuring laser wavefront changes at GHz rates is discussed.

We are developing a laser radar to meet the needs of NASA for a 5-lb, 150 in³ image sensor with a pixel range accuracy of 0.1-inch. NASA applications include structural dynamics measurements, navigation guidance in rendezvous and proximity operations, and space vehicle inspection. The sensor is based on the scannerless range imager architecture developed at Sandia. This architecture modulates laser floodlight illumination and a focal plane receiver to phase encode the laser time of flight (TOF) for each pixel. We believe this approach has significant advantages over architectures directly measuring TOF including high data rate, reduced detector bandwidth, and conventional focal plane array (FPA) detection. A limitation of the phase detection technique is its periodic nature, which provides relative range information over a finite ambiguity interval. To extend the operating interval while maintaining a given range resolution, a LADAR sensor using dual modulation frequencies has been developed. The modulation frequency values can be scaled to meet the resolution and range interval requirements of different applications. Results from the miniature NASA sensor illustrate the advantages of the dual-frequency operation and the ability to provide the range images of 640 by 480 pixels at 30 frames per second.

A simple analytical model of a laser radar's subtended irradiance probability-density-function has been developed for both direct detection and coherent detection laser radar. The vacuum speckle irradiance statistics are developed following Goodman's 'M parameter' treatment for direct detection ladar and also by setting the M-parameter equal to one (negative- exponential power statistics) for coherent laser radar. A 'turbulence M parameter' is then computed using the round-trip aperture averaging analyses of Gudimetla and Holmes based on the Rytov-variance parameter computation over an atmospheric path of interest. The 'vacuum M parameter' and the 'turbulence M parameter' are then combined to form an 'effective M parameter.' This effective M parameter is used in an analytically simple gamma distribution probability-density- function for the laser radar's subtended irradiance. We will show excellent agreement with the more analytically complicated two-parameter K-distribution from the literature. We will also indicate how one may include the turbulence scintillation in addition to the fundamental vacuum speckle, with increasing levels of turbulence to determine ladar performance.

The number of photons returning from a target in a given time interval is a negative-binomially distributed random variable. The resulting detected photon 'electron pulses' produced by a photomultiplier tube (PMT) photon-counting detector are also negative-binomially distributed per time bin with a reduced mean. These time distributed electron pulses are amplified and filtered by the receiver electronics, prior to digitization and signal processing. The voltage output pulse per individual photo-electron event is known as the 'impulse-response- function' of the detector and amplifier. The random summation of these voltage impulse-responses, as created by the negative-binomial photon arrival times and photo-electron creation, is the classical electronic 'shot-noise' random process. We derive the voltage probability density function of this 'negative-binomial driven shot-noise' random process following the stochastic process literature. We also show a technique to include PMT variations in gain, known as the 'pulse height distribution,' and also to incorporate Gaussian baseline-noise voltage. Agreement with several experiments is shown to be excellent.

Physical Optics Corporation (POC) is developing an innovative light illumination system for a continuous wave imaging laser radar that is being investigated at the Army Research Laboratory. The illumination system will combine the output power from a number of laser diodes into one highly collimated beam with a divergence of three angular minutes. This will provide a 10-m diameter illumination spot at a distance of 5 km, and therefore, a high-power illumination field at the object of interest. The illumination system consists of several fiber-coupled laser diodes, mechanical and optical assemblies for focusing light from every fiber to a collimator focus point, and a non-imaging beam combiner-collimator with 180 degree acceptance aperture. The outgoing clear aperture of the combiner-collimator element is about 80 mm; overall the entire illuminator is compact, light-weight, and cost- effective in mass production.

The paper describes recent work on the development of hollow waveguide integrated optic systems with integrated laser sources. Both monolithic and hybrid laser integration concepts have been considered. The hybrid approach has been carried through into the design, manufacture and demonstration of a homodyne system. Details of design, manufacturing and assessment issues, and the demonstration of the system as a Doppler anemometer, will be discussed.

Coherent laser radar and other demanding applications require extremely stable, environmentally immune cw laser sources to act as single frequency references in the Doppler measurement process. Powerful new techniques such as micro-Doppler remote vibration sensing place even greater demands on these reference oscillators, which require sub-kHz absolute reference frequency stability over several milliseconds to resolve sub-mm/sec vibration signatures at many ten's of kilometers range. We report on progress toward super-stable (1 - 100 Hz relative stability over relevant lidar times of flight) cw eyesafe master oscillators for such applications, incorporating active frequency stabilization techniques. We also describe wide band agile frequency offset locking between two frequency-stable oscillators, relevant to the problem of compensating for large platform-induced Doppler shifts in space-borne coherent lidar applications. In these experiments, two cw lasers were programmably offset locked across a +/- 4.5 GHz span, to an accuracy of 5 kHz.

The radiation at around 1.5 micrometer has been extensively investigated over the last few years for eye-safe applications. This paper describes the development and performance of a pulsed solid-state laser based on nonlinear frequency conversion of the Nd:KGd(WO₄)₂ fundamental radiation into the near-infrared region of the spectrum. Neodymium-doped potassium gadolinium tungstate Nd:KGd(WO₄)₂ (Nd:KGW) possesses a combination of spectral and lasing characteristics uniquely favorable for laser operation. The explanation for the high efficiency which can be achieved with this material follows from high effective stimulated- emission cross section of laser transition. Also, in contrast to Nd:YAG, Nd:KGW is an efficient Raman medium. In the present paper most attention has been concentrated on the self- conversion of the laser wavelength at 1.351 micrometer to the first Stokes line at 1.538 micrometer. In conclusion, we have demonstrated a compact low-threshold source for the near-IR in configuration of an intra-cavity solid-state Raman laser based on a flashlamp-pumped Nd:KGW laser crystal. The small size and high efficiency of this laser makes it an attractive source for a large number of applications such as communications and optical atmospheric studies.

We present the concept of a Multispectral Polarization Active Imager operating in the visible range. The acquisition of three degree of polarization (0% < Dp < 100%) images and three intensity images at different wavelengths (RGB) enables to get information about the spectral signature of targets as well as their polarization properties. A theoretical analysis and an experimental validation of this technique are presented. The device is operating in a monostatic configuration, using a white light source to illuminate the target. The reception system consists of a liquid crystal achromatic polarization rotator followed by a liquid crystal color filter and a CCD camera, all driven by a computer. The three polarization images can be merged in one by using a RGB coding in order to visualize the whole polarization information. Results with different targets will be presented, emphasizing polarization effects about backscattering. In particular the degree of polarization is found to be highly correlated to the reflectance of diffuse materials like paints, papers and other coatings. A first interpretation is given to explain this phenomenon. Application to identification of targets with low sensitivity to irradiance can be envisaged thanks to multispectral polarization signature.

In long-range applications, a laser beam propagating through atmosphere or particulate systems is depolarized due to multiple scattering. The transfer function of the state of polarization is given by the Mueller matrix associated to that system. We present here a systematic study of the polarization transfer function associated with multiple scattering systems. Real-time measurements of the Mueller matrix are presented for systems with various optical densities. We have specifically addressed the problem of noise reduction by overdetermining the Mueller Matrix. Experimental results of depolarization effects due to multiple scattering are shown for standard media that mimic atmospheric, plum or underwater propagation. This method aims at: (1) accounting for depolarization effects in long-range target identification and (2) remote monitoring and characterization of particulate systems.

The purpose of active imaging system is to provide discrimination at long ranges independently from the surrounding illumination by using and controlling its own light source. Parameters such as the Doppler shift for coherent devices, the range, or the intensity of the light back scattered by objects have already been used to encode images. However, another parameter characterizing the electromagnetic field can help to discriminate the target: its polarization. In this paper we demonstrate that images resulting from the analysis of the polarization of light can offer better contrasts than classical images encoded by the intensity of light back-scattered. The emitting part of the imaging polarimeter built at CREOL (Polarization State Generator) is a doubled YAG pulsed laser with external polarization controllers. At the receiving part, the Polarization State Analyzer separates the incoming light so as to provide two crossed polarized images of the target.These images are acquired simultaneously by two high-resolution progressive scan digital cameras controlled by a computer. Afterwards, the computer processes the acquired data and displays two new images encoded by polarization parameters (depolarization ratio for example). In several examples and experiments, the influence of the geometry of the target (roughness, shape) on the incident state of polarization will be discussed.

This paper describes a signal processing technique that has been developed for a vibration-sensing laser radar. The sensor has successfully acquired data from moving objects. Vibrations on the surface of the object can be induced by internal machinery and, when stationary, would normally be seen as modulations about a fixed carrier frequency. Thus a straightforward demodulation technique can be used to identify any important vibration characteristics. However, for a moving object, the laser transmit frequency is Doppler-shifted upon reflection by an amount proportional to the object's velocity resolved along the line-of-sight of the sensor. Therefore, the carrier frequency of the return signal is not known and the range of frequencies that it could occupy is large in comparison to the bandwidth of the modulations. The algorithm locates the carrier frequency within some large range (typically tens of Megahertz) and generates a synthetic mixing signal that allows the carrier to be down-shifted to baseband. Tracking is performed using a series of Kalman filters on all likely signal candidates and the synthetic mixing signal is made up of the set that scores highly in terms of carrier-to- noise ratio, for example. Following the mix, the resultant signal is decimated so that modulations corresponding to the surface vibration can be studied. This paper illustrates the signal tracking technique applied to a number of real data sets and discusses the benefits of using a predictive method.

Lidar remote sensing of micro-Doppler signals is important for a large number of civilian and military applications. The single most important performance metric of these sensors is their velocity measurement precision. The velocity precision of a micro-Doppler lidar is limited by any one of various noise sources, which include shot-noise, local-oscillator frequency noise, speckle decorrelation noise, refractive turbulence advection noise and pointing jitter. In this paper, we present a theory, which describes these noise sources and their wavelength dependence. For example, it will be shown that the turbulence advection noise is wavelength independent while speckle decorrelation noise is proportional to the illumination wavelength and that the noise sources are, to a first-order, independent of the interrogation waveform classification (i.e., pulsed or CW). The results from recent field measurements using a doublet-pulse lidar will be compared with theory.

The technique of laser vibrometry is used to generate vibration images, i.e. data cubes where the target vibration amplitude distribution across the target, for a given vibration frequency, is mapped onto the x-y-plane, and frequency varies along the z-direction. Sample vibration images were taken by laser radars at (lambda) equals 10.6 micrometer (CO₂ laser) and (lambda) equals 1.54 micrometer (erbium fiber laser) at ranges over 1 km. The first ever taken vibration images of motorized vehicles at such distances will be presented. Vibration imagery offers new possibilities for target classification, and for investigating and monitoring vibration behavior of large scale structures. Experimental and theoretical comparisons of laser vibrometry techniques with and without spatial resolution capability will be presented.

The goal of this work is possibility investigation for developing of high efficient and high output power mini TEA CO₂ laser Second Harmonic Generators (SHG) applicable to use in mobile gas analysis lidars. Efficiency of SHG with Te, CdGeAs₂, ZnGeP₂, AgGaSe₂ AgIn_0.4Ga_0.6Se₂, Tl₃AsSe₃, and GaSe nonlinear crystals was estimated by solving shortened equations for interacting waves in combination with thermodynamic one. The latter equation allowed us to take into account the crystal self-heating effect (thermal refraction and lens effect) and inhomogeneous disturbance of SHG phase-matching, as well as took into account an energy transfer from the pumping wave to SH, optical losses, aperture and diffraction effects. In so doing we demonstrate SHG efficiencies using the following CO₂ pumping laser parameters: wavelength (lambda) equals 9.3 micrometer, pulse duration (tau) equals 50 ns, pulse repetition rate f equals 1000 Hz, pulse power E equals 50 mJ. The pulse repetition rate satisfies condition of the 'frozen' atmosphere and the energy is sufficiently large for working on topographic targets that are 10 km off using both CO₂ laser emission and its SH (the conversion efficiency is from 5 to tens of percent). Besides, we believed that the laser is operated in TEM₀₀ mode, the pumping intensity was assumed to be a half of the threshold pumping intensity (it provides for stable SHO operation), the time shape and intensity distribution in the beam cross section were assumed to be Gaussian. These parameters as a whole correspond to ones of the typical mini TEA CO₂ lasers, which are used in mobile lidars. Additional angular tuning of the crystals, that maximizes SHG efficiency, as well as the optimal crystal lengths, giving its absolute maximum for the fixed pumping pulse repetition rate, were also determined.

Laser vibration sensing provides a sensitive non-contact means of measuring vibrations of objects. These measurements are used in industrial quality control and wear monitoring as well as the analysis of the vibrational characteristics of objects. In laser vibrometry, the surface motion is monitored by heterodyne laser Doppler velocimetry, and the received heterodyne signal is sampled to produce a time-series which is processed to obtain a vibrational spectrum of the object under test. Laser vibrometry data has been processed with a traditional FM discriminator approach and by spectrogram and time-frequency distribution processing techniques. The latter techniques have demonstrated improved performance over the FM discriminator method, but do not take full advantage of the prior knowledge one has about the signal of interest. We consider here a statistical signal processing approach to laser vibrometry data. In this approach the quantities of interest are the frequencies of vibration, while the phase and quadrature amplitudes are considered nuisance parameters. Because of the optimal use of prior knowledge about the laser vibrometry signal, the frequencies can be determined with much greater precision and greater noise immunity than using Fourier- or time-frequency-based approaches. Furthermore, the statistical approach is known to have superior performance when the data extends over a small number of vibrational periods. We illustrate the method with data from a fiber-optic laser Doppler velocimeter. Our results show that while the choice of processing method for determining the instantaneous velocity is relatively unimportant, the Bayesian method exhibits superior performance in determining the vibrational frequency.

This paper describes the method and algorithms for analysis of moving object image, which was obtained by Doppler laser radar. A Doppler image is 2D image, in which any pixel represents a value of Doppler shift (the radial velocity) for the area element of observed scene. It is difficult for human-operator to percept a Doppler image on radar display. However, Doppler image contains the greater amount ofinformation for computer analysis and automatic determination ofobject features. For features extraction of dynamic object, we propose to analyze the projections of Doppler image in coordinates an horizontal direction - Doppler shift and vertical direction - Doppler shift, named as Space-Doppler projections. SpaceDoppler projections are mutual associated images and they have unique form for each type of object. For example, SpaceDoppler projections of moving car look like letter H, have clearly recognizing areas of rotating wheels and car body. The detailed analysis of Space-Doppler projections allow to define the angular position of car wheels, the line of land osculation, line connecting centers of rotating wheels, size of wheels, space orientation of car and other features. This information allows to create the formalized description ofobserved object and to define its type.

There are several techniques for performance evaluation of an imaging system (IS). The first is the classical one: performance is considered as a characteristics called minimum resolvable temperature difference (MRTD). The second one is fidelity which is a parameter based on the least-square error between output signals of the idealized IS and an investigated one. The least-square error takes into account noise and distortions introduced by high spatial frequencies suppression. The third technique is defined via correlation coefficient between output signals of the idealized IS and a definite one. The paper discusses the application of the mentioned approaches for performance evaluation.

This paper presents the results of experimental studies and design development of basic models of uncooled compact pulsed lasers with lamp pumping. The lasers are intended not only to be used independently but also to function as component of optoelectronic devices. The mass of the radiators is 50 - 200 g. A modern set of components, developed at the S. I. Vavilov State Optical Institute, is used in the radiator. It is envisaged that it will be simple to replace the individual modules and elements and that additional optical devices can be built in.

This paper presents a model used to predict the performances of a burst illumination imaging lidar propagating through the atmosphere. The laser beam propagates near the ground on a long distance and undergoes strong perturbations due to atmospheric turbulence. This model takes into account both propagating paths: forward propagation as the wavefront progresses towards the observed object and backward propagation as the light is reflected back to the receiver.

The Russian Mjasishchev 55 (M-55) <<Geophysica>> high altitude aircraft is dedicated to atmospheric science research. It carries onboard a set of mutually complementary instruments for in- situ and remote sensing. The Green Miniature Aerosol Lidar (GMAL) has been developed to operate automatically on this platform. It is a short-range, zenith-looking, depolarization elastic-backscatter lidar based on a 532 nm micro-chip Nd-YAG laser. Compact, low-power consuming, it stands in a 27-litre isolating and warmed hermetic box. The device participated successfully to an extended test campaign in Italy during December 1998 and January 1999, and to the APE/THESEO campaign in the Indian Ocean during February-March 1999. It also showed capabilities for unattended measurement of the low troposphere from the ground. Description of the instrument and preliminary results are presented.

The UAV platform is ideal for remote sensing. A powerful remote sensing tool is a laser based lidar system. Two significant constraints on this platform are the size and mass of payloads. An additional constraint is the opto-mechanical precision required for a diffraction limited lidar telescope. A solution to these challenges can be found using lightweight, stiff carbon fiber composite materials. The authors report on the requirements, design, analysis, and manufacturing of a carbon fiber composite telescope for a UAV platform. In addition to meeting the required precision assembly and tolerances under various load cases, the telescope features a moisture barrier. Typical carbon fiber composites absorb moisture from ambient humidity, causing minute expansion of the material. The moisture barrier of prevents moisture from being absorbed by the material, eliminating distortions in the telescope due to moisture.

It's proposed reaction-diffusion mathematical model for evaluating efficiency and area of destruction of brain's tumor under photodynamic-laser therapy. The modeling is based on physical mechanism of tissue's effect by singlet oxygen, which display oxidizer's function. Kinetic description of process is proceeded from model of M.J.C. van Gemert, that was worked out diffusion's mechanism of oxygen's spreading in tissue. All calculations are carried out for red laser with wavelength 630 nm and photofrin2, as photosensitizer. The space-time dependencies of concentrations of possibility conditions of oxygen and photosensitizers are calculated. As was theoretical shown, effect of photodynamic destruction of tumor, particularly in brain, not depends from intensity of laser's irradiation, but depends from summation of dose, which is absorbed by tissue in all time of process. The temperature's effects in tumor, that accompany of photodynamic therapy, were calculated also.