The Air Force Wright Laboratory has successfully flown two micron laser radars and is preparing to fly a third. These systems are designed to provide real-time 3D maps of the wind fields between the aircraft and the ground. This paper briefly describes these systems and the demonstrated performance of each. Future measurement efforts of this program ar also discussed.

Recently NASA Langley Research Center's (LaRC) Aerosol Research Branch conducted an aircraft exhaust particle experiment involving tow ground based lidar systems and NASA's B737-100, T39 and OV10 aircraft. The experiment took place at LaRC in February and March of 1996. During flight, exhaust particles exiting the two wing-mounted engines of the B737 become quickly entrained into the aircraft's wingtip vortices. The LaRC lidar systems were used to measure the distribution and optical properties of these exhaust particles as the B737 overflew the lidar facility. Two lidar systems, located in a common facility, were utilized for this experiment. One system was a fixed zenith- viewing lidar with a 48-inch receiver and a 2J transmitter, and the second was a scanning lidar with a 14-inch receiver and a 600 mJ transmitter. Two measurement geometries were employed for the experiment. In the first geometry, the B737 flew upwind of the lidar facility and perpendicular to the ambient wind. The second design had the aircraft fly directly over the facility, and parallel to the ambient wind.Under either scenario data were acquired at 20 and 30 Hertz, by the fixed zenith and scanning system respectively, as the ambient wind carried the vortex pair across the field of view of the lidars. The two supporting aircraft were used to collect in-situ particle data and to measure atmospheric turbulence, respectively. In this paper all aspects of the experiment will be discussed including the lidar systems, the geometry of the experiment, and the aircraft used. Also, selected data obtained during the experiment will be presented.

Active imaging laser radars form 3D images which can be processed to provide target identification and precision aimpoint definition in real time. Earlier raster-scanned and pushbroom-scanned 3D imaging laser radar receivers required multiple laser pulses to assemble a complete 3D image frame. Platform/target motion and atmospheric effects caused tearing and jitter in the assembled 3D images, which complicated the subsequent image processing and necessitated the use of stabilized scanning systems. This paper describes the current status of the parallel/multichannel imaging laser radar receiver (PMR) which is being developed under an SBIR Phaser II program by the USAF Wright Laboratories Armament Directorate. The PMR uses an array of multichannel laser radar receivers to form single-pulse, 3D laser radar images, thus eliminating the complex and costly scanning system, and enabling much higher frame rates than were ever before possible. The heart of the PMR is the multichannel optical receiver photonic hybrid (MORPH), a high performance 16-channel laser radar receiver module which uses an array of InGaAs avalanche photodiodes for eyesafe operation. The MORPH provides high downrange resolution, multihit range data for each detector on a compact circuit card. Optical flux is transferred from the receiver focal plane to each MORPH via a fiber optic ribbon cable. An array of MORPHs are plugged into a compact passive backplane, along with a single digital control card (DCC). The DCC, which is the same form factor as the MORPH, synchronizes the MORPHs and transfers the digital range information to the host processor over a standard parallel data interface cable. The system described here illustrates one approach to integrating and packaging high-density photonic arrays and their associated signal processing electronics to yield a compact, low power, scannerless, high performance imaging laser radar receiver, using existing technology.

We investigated laser radar technology for tactical intelligence; that is, we wanted to build a camcorder-sized device for information on terrain, and for reconnaissance and surveillance of various targets. Our performance requirements were; field of view 15 mrad by 150 mrad, image resolution 0.15 mrad, range 1 km, range depth resolution 15 cm, and acquisition time one third of a second. We designed imaging devices using two of the most promising technologies that we found. The first imager uses a digital CCD camera with a modulated image intensifier. The laser is a Q- switched, flashlamp-pumped, Nd:YAG laser. THere is no scanner in this system. The range is obtained by a technology similar to classical continuous phase detection. The second imager uses a diode-pumped solid state laser, and fiber optics to relay the image to thirty-two avalanche photo-diodes. The laser beam is split into thirty-two beams and a binary optics scanner is used for scanning between beams. The range is obtained with time-of-flight electronics. BOth imaging system designs meet the basic requirements, and could also be used in automatic target recognition, aimpoint selection, target tracking, obstacle avoidance, and other imaging laser radar applications.

A kilowatt class, pulsed CO₂ laser radar has been developed at Textron under a joint US Army-Air Force program. It is currently undergoing field trials; and successful coherent imaging and tracking experiments have been conducted over the past two years at the Air Force Maui Space surveillance Site. This paper describes the receiver- processor architecture of the laser radar system, the algorithms and waveforms, and the output products which are high resolution range-Doppler and range-amplitude image. Attention will be paid to the hardware and software methods used to achieve real-time, wideband operations.

The HI-CLASS is a high power, wideband, coherent laser radar for long range detection, tracking, and imaging located at the Maui Space Surveillance Site (MSSS). HI-CLASS will be used to provide high precision metrics as well as information for images of space objects and remote sensing with the same system. The HI-CLASS system is currently in the final of four phases. During Phase 1, breadboard hardware was built which led to a fully integrated laser radar system at MSSS. During Phase 2, an improved system oscillator and receiver-processor were built and integrated which brought the system capability to 12 Joules at 30 Hz. The Phase 3 system has the addition of a power amplifier to the transmitter which brought the system capability to 30 Joules Hz. The HI-CLASS system will validate technology and designs required for fielding operational systems since it has the potential to address operational areas of need for increased capability for information about space objects. HI-CLASS will provide high accuracy tracking in position and velocity simultaneously, and by ultimately providing size, shape and orientation information which will help assess adversary capabilities.

The detection and processing of laser communication signals are drastically affected by the fading induced onto these signals by atmospheric turbulence. One method of reducing this fading is to use an array of detectors in which each of the detector outputs are added together coherently. This requires measuring the phase difference between each of the receivers and co-phasing each of the detector outputs. This paper presents experimental verification at the Innovative Science and Technology Experimentation Facility over an outdoor range of a 1.06 micron eight element coherent receiver used to mitigate the effects of fading. The system is composed of a 60 mw Nd:Yag laser used as the transmitter and a 27 MHz AO modulator used to frequency shift the transmitted beam. The receiver is composed of eight 1 cm lenses launching the eight received optical signals into eight signal mode optical fibers. Phase compensation between each of the eight receivers is accomplished using single mode fibers wrapped around PZT cylinders that are controlled by phase compensating electronics. The carrier-to-noise (CNR) ratio was measured on a single channel and was then compared with the CNR obtained from the coherent sum of the eight channels. The improvement of the CNR for the coherent sum as compared to a single channel was then compared against theoretical predictions.

The effects of round-trip atmospheric turbulence on ladar for unresolved target detection are being investigated using a Monte Carlo code with many phase-screens to simulate atmospheric turbulence effects. These phase-screens are located along the outward path of the laser-mode and the inward path of the backscattered laser speckle pattern. The targets used are variable in size and smaller than the propagated laser-mode transverse dimension, and they are therefore termed 'unresolved'. In this paper previous round- trip turbulence analyses and data are reviewed, and the current Monte Carlo simulation code for unresolved targets is discussed. Simulation results to date are presented indicating that intensity fluctuations are best described by a new two-parameter K-distribution probability density function. This intensity distribution may then be used in deriving a ladar receiver-operating-characteristic for determining the target detection probability including round-trip turbulence.

Laser radar image of an outdoor target scene were collected in adverse weather such as rain and fog during the course of one year. Included in this collection is imagery in fogs with visibilities less than 0.2 km and rains with rain rates of up to 180 mm/hr. The targets were small buildings, target panels and a mobile target, all approximately 500 m in distance from the laser radar system. The laser radar system used was a direct-detection 1.06 micrometers system designed to operate at 1 km in clear weather. Using these collected images, dropout pixels and false returns were correlated with rain rate and visibility. Dropouts and false returns were found to follow a linear relationship with rain rate and an exponential decreasing relationship with visibility. Empirical equations were developed from least square fits of the data to predict the dropouts and false returns, given the rain rate and visibility. Finally, fog and rain data from 450 images was combined and correlated into visibility intervals so that one can predict the dropout and false return percentages given a visibility in either fig or rain.

This paper summarizes the theoretical and experimental results on the problems into the development and application of adaptive systems, obtained at the Laboratory of Applied and Adaptive Optics. The problems of adaptive systems evolution are underlines, i.e., developing of modern numerical models and performing of structural analysis of the most promising algorithms of adaptive correction. We are developing the methods and setups for sounding of optically- active atmospheric layer as well as the models of the atmosphere.

NASA's Marshall Space Flight Center has developed an active sensor system, the ideo guidance sensor (VGS), to provide near-range relative position and attitude data. The VGS will be part of an automatic rendezvous and docking system. The VGS determines the relative positions and attitudes between the active sensor and the passive target. It works by using laser diodes to illuminate the retro-reflectors in the target, a solid-state camera to detect the return from the target retro-reflectors, and a frame grabber and digital signal processor to convert the video information into relative positions and attitudes. The current sensor design is the result of several years of development and testing, and it is being built to fly as an experiment payload on the space shuttle. The VGS system is designed to operate with the target completely visible within a relative azimuth of +/- 10.5 degrees and a relative elevation of +/- 8 degrees. The system will acquire and track and target within that field-of-view anywhere from 1.0 meters to 110 meters range at any relative roll angle and relative pitch and yaw attitudes of up to +/- 10 degrees. The data is output from the sensor at 5 Hz, and the target and sensor software have been designed to permit two independent sensors to operate simultaneously for redundancy.

The video guidance sensor is a key element of an automatic rendezvous and docking program administered by NASA. The system sues laser illumination of passive target in the field of view of an on-board camera and processes the video image to determine the relative position and attitude between the target and the sensor. Theoretical predictions and evaluations, and laboratory measurements and test are presented for the lasers, target components, camera system, signal processor, and a solar simulator.

The ROBS instrument has recently acquired unique imagery of a missile intercepting an airborne drone target. We present a summary of that mission. We also present imagery of three airborne targets collected while the ROBS instrument simultaneously tracked all three aircraft. The recent test data highlights the capability of the ROBS instrument for autonomous acquisition, tracking, and imaging of multiple targets under field test conditions. We also describe improvements to the optical system currently underway.

The Armament Directorate of Wright Laboratory is tasked with pursuing technologies that lead towards autonomous guidance for conventional munitions. Seeker technologies pursued include SAR, imaging infrared, millimeter wave, and laser radar seekers. Laser Radar, or LADAR, systems using uncooled diode pumped solid state lasers operating around 1 micrometers are active sensors providing high resolution range and intensity imagery. LADAR is not susceptible to variations common to thermal IR systems, allowing greater simplicity of autonomous target acquisition algorithms. Therefore, LADAR sensors combined with advanced algorithms provide robust seeker technology capable of autonomous precision guidance. The small smart bomb (SSB) is a next generation weapon concept requiring this precision guidance. The 250 pound SSB penetrator provides the lethality of 2000 pound penetrators by delivering 50 pounds of high explosive with surgical precision. Space limitations, tightly controlled impact conditions, and high weapon velocities suggest laser radar as a candidate seeker. This paper discusses phase I of the DASSL program in which SSB weapon requirements are flowed down to seeker requirements through a structured system requirement analysis, and discusses how these seeker requirements affect seeker design.

A high repetition rate 10Hz diode side pumped erbium glass laser transmitter for rangefinder and radar applications was demonstrated. Without cooling it was operated at 10Hz for more than 30 seconds. With forced air it was run continuously at 10Hz with an output of 5-10mj and 25-30nsec pulsewidth.

We are presenting the status of an eyesafe laser radar under development at NAWCAD. It is based on a Nd:YAG pumped LiNbO₃ or KTA OPO operating near 1555 nm combined with a 7.5 inch aperture receiver and an InGaAs detector. Results at ranges beyond 10 km and against various targets will be presented.

Recent advances in high powered laser diodes and fiber optic coupling a low efficient integration of laser systems into existing gimbal systems. A high power, divergent beam can be used to illuminate a scene providing enhanced performance in poor weather, the recording of registry and augmentation to existing night vision devices. This paper describes the enabling technologies, applications and performance or recording alphanumeric.

Previous efforts to develop 3D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes an approach that will enable a complete 3D ladar image to be captured with a single pulse. Using a unique processor chip that is bump bonded directly behind the 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. This paper will discuss the status of the imager that is being assembled as well as preliminary results form field demonstrations. The specifications of the demonstration unit are for a 32 by 32 pixel imager with a resolution of .3 by .3 by .3 meters. The system is expected to operate at approximately video framing rates and the resulting image will be displayed in a false color picture on the processor monitor.

The concept of a wide field-of-view coherent detection insensitive to the wavefront distortions of the signal to be detected is proposed. The principal of this detection is based on two-wave mixing in photorefractive materials. The experimental validation of this concept is demonstrated at (lambda) equals 0.5 micrometers using a photorefractive crystal of Bi₁₂SiO₂₀. The sensitivity of the detection is theoretically and experimentally analyzed. It led to the conception of a wide field-of-view coherent detection demonstrator operating in the eye-safe band using a photorefractive crystal of CdTe. The application of this device to vibrations analysis of a mechanical structure and the determination of its resonance frequency are demonstrated.

Many problems exist in ophthalmology, where accurate measurements of eye structure and its parameters can be provided using optical radar concept is of remote sensing. Coherent and non-coherent approaches are reviewed aiming cornea shape measurement and measurement of aberration distribution in the elements and media of an eye. Coherent radar techniques are analyzed taking into account non- reciprocity of eye media and anisoplanatism of the fovea, that results in an exiting image being not an auto- correlation of the point-spread function of a single pass, even in the approximation of spatial invariance of the system. It is found, that aberrations of the cornea and lens are not additive, and may not be brought to summary aberrations on the entrance aperture of the lens. Anisoplanatism of the fovea and its roughness lead to low degree of coherence in scattered light. To estimate the result of measurements, methodology has been developed using Zernike polynomials expansions. Aberration distributions were gotten from measurements in 16 points of an eye situated on two concentric circles. Wave aberration functions have been approximated using least-square criterion. Thus, all data were provided necessary for cornea ablation with PRK procedure.

The linear frequency-modulation chirp pulse compression technique of classical microwave radar is examined in the context of coherent laser radar. A coherent CO₂ laser radar may operate near 9.115 micrometers and 33,000 GHz. Because of this short wavelength, a large target Doppler-spread is realizable in a single ladar measurement. In addition, target surface roughness with respect to wavelength causes the target backscatter points to be uniformly distributed over 2(pi) radians in phase resulting in Gaussian/Rayleigh/negative-exponential receiver statistics. Target Doppler spread and speckle as well as target down- range extent affect the linear-FM-chirp pulse compression efficiency thereby degrading the peak compressed-pulse carrier-to-noise. This degradation in carrier-to-noise is quantified using a 'maximum of M Rayleighs' detector model which allows a simple scale factor degradation for other coherent ladar wavelengths, chirp magnitudes, and pulse lengths. The receiver-operating-characteristic of the sum of many Rayleigh distributed random variables is also developed for comparison to the classical sum of many negative- exponential statistics.

The relationship between two different motions which influence beam displacement in space, the movement of the flight vehicle and the rotation of the deflector were studied in a case of across-track scanning. The general equations were derived. The mathematical model of data processing was presented. The simulation of a 3D beam scanning was performed using the MATLAB-software.

This paper presents the signal processing method of laser images used for detection of small collinear obstacles in helicopter airborne applications. It is very difficult, if not almost impossible, for a regular passive imaging sensor based on CCD/FLIR detectors to detect such small, remote objects. It was shown in the literature that the fusion of range and intensity data is needed for such a task. The paper presents a new and improved algorithm for real time image processing which enable detection of small tiny objects, from a fast moving platform. Two issues related to 3D visual sensing from laser sensors are addressed here. First, concerning the filtering and reduction of the large amount of data to be coped with for enabling real-time detection with low false alarm rate, in any ambient light conditions. Second, the fusion of range and intensity data for detecting small objects form cluttered data with high probability of detection. The preliminary experimental results show the potential of the proposed algorithm, based on spatio-temporal integration, to detect with high probability such objects like electrical cables from ranges of up to 400 meters.

It is solved the problem of the velocity maximum likelihood estimation for laser Doppler velocimeter. It is found also potential accuracy of this estimation.

Many vehicle targets of interest to military automatic target recognition (ATR) possess articulating components: that is, they have components that change position relative to the main body. Many vehicles also have multiple configurations wherein one or more devices or objects may be added to enhance specific military or logistical capabilities. As the expected target set for military ATR becomes more comprehensive, many additional articulations and optional components must be handled. Mobile air defense units often include moving radar antennae as well as turreted guns and missile launchers. Surface-to-surface missile launchers may be encountered with or without missiles, and with the launch rails raised or lowered. Engineers and countermine vehicles have a tremendous number of possible configurations and even conventional battle tanks may very items such as external reactive armor, long- range tanks, turret azimuth, and gun elevation. These changes pose a significant barrier to the target identification process since they greatly increase the range of possible target signatures. When combined with variations already encountered due to target aspect changes, an extremely large number of possible signatures is formed. Conventional algorithms cannot process so many possibilities effectively, so in response, the matching process is often made less selective. This degrades identification performance, increase false alarm rates, and increases data requirements for algorithm testing and training. By explicitly involving articulation in the detection and identification stages of an ATR algorithm, more precise matching constraints can be applied, and better selectivity can be achieve. Additional benefits include the measurement of the position and orientation of articulated components, which often has tactical significance. In this paper, the result of a study investigating the impact of target articulation in ATR for military vehicles are presented. 3D ladar signature data is used. An algorithmic solution is proposed and directions for further research are noted.

We investigate the phenomenology and modeling for the development of an active multispectral laser radar (LADAR) sensor to image and identify ground targets in the 1 to 5 micrometers wavelength region. This sensor will be especially useful in high clutter situations or situations where the target is partially concealed. A continuously tunable optical parametric oscillator using a periodically poled lithium niobate (PPLN) nonlinear optical crystal is investigated as a candidate light source for the sensor. A 1 micrometers Nd:YAG laser was frequency shifted in PPLN to produce continuously tunable output between 1.35 to 5 micrometers wavelengths and signal output energy of up to 3.3 mJ in a 3 ns pulse. A tunable monostatic reflectometer system is fabricate for the measurement of the bidirectional reflectance distribution function of the LADAR target materials A method or band selection is formulated and tested using library reflectance spectra. Results of this work will be used for tower based imaging of different targets in cluttered backgrounds at ranges out to 3 km.

This paper discusses the development of an imaging laser radar system working with a gated viewing camera at the eye- safe wavelength of 1574nm. The system is compared to an eye- safe imaging scanner system at 1574nm and a gated viewing system working at 532nm. The requirements for the system are a range between 0.5 to 4km at bad weather conditions and a high vertical and horizontal resolution. Therefore we examine the different imaging laser radar systems with a computer simulation tool, especially the capabilities and performance at different weather conditions. The laser radar should be part of a real-time 3D-visualization system for enhanced and synthetic vision to detect real objects in the field of view.

BNL has been developing a remote sensing technique for the detection of atmospheric pollutants based on the phenomenon of resonance Raman LIDAR that has also incorporated a number of new techniques/technologies designed to extend its performance envelope. When the excitation frequency approaches an allowed electronic transition of the molecule, an enormous enhancement of the inelastic scattering cross- section can occur, often up to 2 to 4 orders-of-magnitude, and is referred to as resonance Raman, since the excitation frequency is in 'resonance' with an allowed electronic transition. Exploitation of this enhancement along with new techniques such as pattern recognition algorithm to take advantage of the spectral fingerprint and a new laser frequency modulation technique designed to suppress broadband fluorescence, referred to as frequency modulated excitation Raman spectroscopy and recent developments in liquid edge filter technology, for suppression of the elastic channel, all help increase the overall performance of Raman LIDAR.

Lidar systems developed over the last decade have demonstrated impressive results when applied to the detection of specific volatile chemicals. MOst of these systems are limited to a single wavelength or, at best, a narrow wavelength band. Exceptions are DIAL systems, CO₂ lidars, and dye laser sources. Currently under development at INEEL and PASSAT Ltd. are technologies that convert Nd:YAG laser energy to the 8-11 micrometers band with an output of 20 millijoules/pulse or higher. Wavelength shifting is accomplished using a tunable optical parametric oscillator and amplifier, and stimulated Raman scattering cells as the emitter. This system can be made tunable continuously from 6-11 microns which makes this an eyesafe laser system. In addition, identical SRS cells are used as low noise, narrow band receivers that are sensitive to extremely low levels of scattered laser radiation. Use of this technology is to generate a pair of pulses at different wavelengths for DIAL applications. A description of this system will be provided along with test results.

ABLE ACE was a high-altitude, laser-propagation experiment in which a series of measurements were made of laser propagation between two aircraft flying at 13 to 14 km altitude and at up to 200 km separation. The measurements included a pupil plane scintillation image, an atmospheric tilt sensor, a wavefront sensor, and a differential phase measurement, across a 50 cm aperture. In addition, a small- aperture, high-bandwidth scintillometer and simultaneous aerothermal-probe measurements were made. The purpose of these measurements was to validate wave-optics propagation codes for high-altitude, long horizontal-path propagation, and to better understand what parameters were important to include in the codes. Additionally we sought to directly understand laser propagation characteristics in the regimes of the flights. This paper provides an overview of ABLE ACE. It discusses the sensor suite, the missions, and the code validation methodology as well as the conclusions of the program.

The US Air Force Phillips Laboratory recently completed an extensive series of flight test experiments to determine the effects of optical turbulence in the 35,000 to 47,000 foot altitude regime. The test series, known as ABLE ACE or Airborne Laser Extended Atmospheric Characterization Experiments, yielded the most precise information on the effects of stratospheric turbulence on laser beam propagation than has ever been previously obtained. The data gathered by this technology program is essential for validating laser beam propagation models and simulation tools used for designing and building the Air Force's Airborne laser. The high vibration environment of an airborne platform poses a unique requirement for scientific instruments that are designed to yield estimates of image and wavefront quality. This paper describes the primary optical sensor used to gather that data. The instrument is a differential phase measuring interferometer that is also insensitive to local turbulence effects.

The ABLE ACE experiment involved measurements of effects of stratospheric turbulence on the propagation of laser beams over nearly horizontal paths between two aircraft flying in the vicinity of the tropopause. The simulations described in this talk were performed in support of the ABLE ACE data reduction effort, and as a means of anchoring the validity of the propagation codes and the atmospheric turbulence models used in these codes. At the outset of this work we were unsure whether the standard turbulence models applied at the altitudes of interest. Turbulence parameters at issue in this regard are the: (1) the spectrum, (2) the inner and outer scale lengths, and (3) the strength as a function of position along the path. Most of the simulations assumed a Kolmogorov spectrum with finite inner and outer scale lengths; and we believe that the ABLE ACE data are consistent with these assumptions. Anemometer and scintillometer measurements of turbulence strength in ABLE ACE indicate that stratospheric turbulence is highly intermittent. Techniques for accounting for this intermittency in the simulations will be discussed. Comparison of simulation results and predictions of theory for weak turbulence indicates that the codes accurately model such effects.

As a segment of a broader program to assess optical properties of the atmosphere in the vicinity of the tropopause, the refractive index structure constant was measured by an airborne anemometry method. This paper discusses details of the anemometer, its implementation as well as some results. The anemometry method emphasizes turbulence with horizonal scales lying between 6 meters and 60 meters. A subsequent overflight, to be reported elsewhere, of the 50 MHz radar at White Sands Missile Range indicates that the horizontally derived structure constants, C_n², are comparable to the vertically derived structure constants obtained from radar. For some flights C_n² appears to be log-normal at least in the asymptotic sense, i.e. only for small deviations from the mean. Large deviations are clearly sub log-normal and occur less frequently than would be the case were the structure constant a true log-normal variable. On other flights inhomogeneity was encountered in the sense of an exit form one air mass and entry into a second. This condition resulted in a bimodality of the statistics. On the whole, however, the entire data set collected in pat over the far east and in part of the western US also appears to be well approximated by an overall log-normal distribution in spite of the obvious inhomogeneity of the atmospheric masses encountered in the collection.

A low noise, high resolution Shack-Hartmann wavefront sensor was included in the ABLE-ACE instrument suite to obtain direct high resolution phase measurements of the 0.53 micrometers pulsed laser beam propagated through high altitude atmospheric turbulence. The wavefront sensor employed a Fired geometry using a lenslet array which provided approximately 17 sub-apertures across the pupil. The lenslets focused the light in each sub-aperture onto a 21 by 21 array of pixels in the camera focal plane with 8 pixels in the camera focal plane with 8 pixels across the central lobe of the diffraction limited spot. The goal of the experiment was to measure the effects of the turbulence in the free atmosphere on propagation, but the wavefront sensor also detected the aberrations induced by the aircraft boundary layer and the receiver aircraft internal beam path. Data analysis methods used to extract the desired atmospheric contribution to the phase measurements from the data corrupted by non-atmospheric aberrations are described. Approaches which were used included a reconstruction of the phase as a linear combination of Zernike polynomials coupled with optical estimator sand computation of structure functions of the sub-aperture slopes. The theoretical basis for the data analysis techniques is presented. Results are described, and comparisons with theory and simulations are shown. Estimates of average turbulence strength along the propagation path from the wavefront sensor showed good agreement with other sensor. The Zernike spectra calculated from the wavefront sensor data were consistent with the standard Kolmogorov model of turbulence.

The problem of tracking of a ballistic missile during the boost phase is very challenging and is of high interest to the Airborne Laser Program (ABL). One of the components of accomplishing missile tracking is the ability to compensate for the tilt induced by the atmosphere. The ABL technology program's airborne laser extended atmospheric characterization experiment project included the task of measuring the atmospheric tilt. This effort was accomplished by propagating an optical beacon from one aircraft and receiving it at a second aircraft using a quad cell detector. This paper will describe how the Air Force obtained the atmospheric tilt calculations from quad cell data that was corrupted with noise. A comparison to ray optics tilt simulations was sued throughout to understand the data and evaluate the noise sources. The result is a comparison of simulated data and measured data with explanations of observed differences.

This paper describes the differential phase experiment (DPE) which formed a major part of the ABLE ACE suite of experiments conducted by the Air Force. The work described covers the rationale for the experiment, the basic experimental concept, the analysis of the differential phase, the optical and software design analysis, a discussion of the polarization scrambling characteristics of the optics, calibration of the equipment and a presentation of some of the major results of the data reduction effort to date. The DPE was a propagation experiment conducted between two aircraft flying at an altitude of 40,000 feet whose purpose was to measure the phase difference between two beams propagating at slightly different angels through the atmosphere. A four bin polarization interferometer was used to measure the differential phase. Due to the high level of scintillation that was presented branch points were present in the phase function. Rytov theory, wave optics simulation and the experimental measurements are in general agreement. Self consistency checks that were performed on the data indicate a high level of confidence in the results. Values of C_n² that are consistent with the measurements of the differential phase agree with simultaneous scintillometer measurement taken long the same path in levels of turbulence where the scintillometer is not saturated. These differential phase based C_n² estimates do not appear to saturate as is typical of scintillometer measurements and appear to extend the range over which high levels of C_n² can be estimated. In addition the differential phase and anisoplanatic Strehl computed from the data is consistent with Rytov theory and wave optics simulations.

The ABLE ACE pupil plane imaging experiment (PPI) measured the irradiance distributions of individual pulses originating from two laser sources on the ABLE ACE transmitter aircraft and incident upon the aperture of the receiver aircraft. The laser pulses were very short, and PPI has high spatial resolution but very low temporal sampling, so the PPI data is simply a series of uncorrelated snapshots of the illuminated aperture.Form the PPI data we can compute the irradiance variance, the probability density function of irradiance, the irradiance covariance function, and the amplitude correlation function, and other irradiance statistics. These statistics can be used for comparison with theory, simulation, and other measurements, and also to estimate the strength of turbulence. The amplitude correlation function is a direct measure of the Strehl ration and optical transfer function that would be achieved with perfect phase correction; this gives us an upper bound on the performance of an actual ABL system. We have PPI data from all ABLE ACE flights, over almost all of the time the science lasers were firing. We have compared PPI results with theory, simulation, simultaneous measurements, and a previous experiment. We see good agreement on all counts.

The idealized performance of a direct-detection differential absorption lidar (DIAL) with an atmospheric backscatter reference has been previously formulated using a radar range equation for meteorological echoes. Performance of several systems is describe here under the assumptions of non- Gaussian speckle and log-normal atmospheric differential backscatter noise. Performance evaluations are presented in detail for a NO₂ detection system. Discussions on the preferred wavelengths for candidate gases, and a review of a new laser radar DIAL performance equation are presented.

Optical measurement of the Doppler shift of laser backscatter, using a near-IR, visible, or ultraviolet laser, is potentially more robust and field reliable than coherent, heterodyne measurement with an IR laser. The direct measurement of the displacement of Fabry-Perot interference fringes is possible, but entails expensive, technically challenging, imaging detectors. The 'edge technique' permits Doppler shift measurements with relatively simple detectors and detector electronics, and has been implemented with Fabry-Perot etalons and with atomic line filters. Simple analytical models of the fringe imaging and edge detection techniques are presented, permitting ready calculation of the potential performance of either, for various atmospheric conditions and for various lidar hardware configurations. The predictions of the analytical models are confirmed by computer models, which in turn allow more detailed considerations of complicating factors such as solar backgrounds and the Rayleigh backscatter signal It is shown that, in virtually all cases of practical interest, for a given lidar signal level, the fringe imaging technique, implemented with either a tunable laser or with a tunable etalon, will yield substantially higher wind speed measurement precision than the edge technique. The result support cost-benefit comparisons of the two approaches to direct detection Doppler wind speed measurement.

We define two simple metrics for accuracy of models built from range imaging information. We apply the metric to a model built from a recent range image taken at the laser radar Development and Evaluation Facility, Eglin AFB, using a scannerless range imager (SRI) from Sandia National Laboratories. We also present graphical displays of the residual information produced as a byproduct of this measurement, and discuss mechanisms that these data suggest for further improvement in the performance of this already impressive SRI.

This paper describes the satellite laser ranging system which was integrated and operated by the Naval Research Laboratory at the USAF Phillips Laboratory's Starfire Optical Range. A 300 mJ, 250 ps, 10 Hz doubled Nd:YAG laser system has been integrated on the 3.5 meter telescope at that facility. It operated in a campaign driven mode from March, 1995, to March, 1997. During that time, NRL at SOR has provided support to the Geoscience community for spacecraft as low as GFZ and as high as GPS; been key in an international SLR campaign to improve the orbits of the GPS NAVSTAR satellites which have retroreflectors; supported the Tether Physics Experiment in Space and obtained the first laser radar returns from that target; externally calibrated for the first time the NAVSPACMD 'fence' receivers; and obtained data on 'unenhanced' targets at LEO.