An eye safe Ho:YAG laser operating cw at 2.09 micrometers was used as the transmitter for this laser radar (ladar) system. The diode pumped Ho:YAG laser provided up to 100 mW of single frequency output power. An InGaAs detector was selected as the off-set homodyne receiver for vibration signatures. This paper describes the design and characteristics of the laser vibration sensor that is based on laser Doppler radar. Initially, the sensor was calibrated using a piezoelectric loudspeaker, then vibrational signatures were obtained for automobiles having four and eight cylinder engines. This two micron laser Doppler radar permitted high- resolution vibrational signatures detection, remotely, at ranges up to 50 meters.

The Scanning Laser Vibrometer (SLV) is becoming widely used as a cost effective tool for automated vibration measurement and analysis of aerospace structures and components. Applications include developing techniques for identifying damage in commercial aircraft, analyzing damage initiation mechanisms during environmental testing of circuit boards and optimum locations for active vibration dampers. The primary advantage of the SLV is the speed with which vibrational velocity measurements can be made over an area. An SLV scan of a structure such as the interior of a fuselage, gathering multi-frequency phase and amplitude values at every point, can be accomplished in less than the time taken to attach and acquire data from a single accelerometer. Results are superimposed in color on a digitized video image of the area tested. Laser vibrometers that offer finer velocity resolution, wider operating range and higher linearity are now available in a fully automated scanning package with ultra-high optical sensitivity. This optical sensitivity for testing untreated areas such as flat black surfaces of graphite composites has been limited in the past to low frequencies and amplitudes. Low optical sensitivity has especially restricted applications such as damage detection -- until now.

A coherent laser radar system based on semiconductor laser technology has been designed and built. The compact design and the absence of adjustments makes the system mechanically robust and easy to use. The present system has an output power of 50 mW and a line width of 280 kHz (HWHM). The laser radar system has been used in vibrometry measurements. For vibrometry of moving objects, adaptive signal processing is required in order to obtain the vibration signature. Especially for unresolved objects, interference between different vibrating parts will complicate the analysis. Model based estimation techniques are used to obtain the parameters which determine the dynamics of the reflecting object.

Studies of various multicomponent laser Doppler radar (MLDR) demonstrated that polarization phase effects of scattering can in some cases considerably affect the signal-to- noise (s/n) ratio of the Doppler signal. A study of the Doppler signal is possible on the basis of the vector scattering theory and optical coherence theory. Simple expressions of the Doppler signal at the photodetector output, the polarization matching coefficient and photocurrent modulation depth for MLDR with a small angle between probing beams using various polarizations were arrived at. Analysis of these expressions demonstrates that if the probing beams have linear mutually orthogonal polarizations then intense influence of the polarization effects on the Doppler signal can be observed in the scattering plane with an angle of 45 degrees. On the basis of generalized results of the conducted studies of Doppler signal parameters for different probing beams' polarization, general properties of changes in Doppler signal's phase, that are observed independent of the scattering particles' parameters, are formulated.

The electric utility marketplace is undergoing tremendous changes. These changes are due in part to the passage ofthe Energy Policy Act of 1992. Under the jurisdiction ofthe Federal Energy Regulatory Commission (FERC), this act requires wholesale wheeling and provides guidelines for requesting and providing such service. Wheeling is the condition whereby a transmission owner has 60 days to respond to a request for transmission service. This act of Congress has an spurred increase in competition among the electric utility companies. The increase in competition due to the "wheeling factor" is not the only challenge that the electric utility market is facing. The increased pressure to control costs; do more with lower operations and maintenance budgets; increase profits; be responsive to environmental agencies; and increase customer satisfaction is causing the electric utility industry to re-examine how it conducts business. Certain traditional methods are being replaced by innovative and cost effective alternatives. The use of technology is seen as a key to combat these challenges and to provide the leverage over the competition. One cost of particular concern to the electric utilities is the surveying of transmission line rightof-ways. Surveying may be due to maintenance upgrades, new line construction, engineering conductor sag studies, facilities mapping efforts, or in response to wheeling requests. The traditional method of manual surveys is slow and can cost several thousand dollars per mile. In some cases the surrounding terrain makes the manual survey efforts almost impossible. In addition, the right-of-ways may need to be inspected on a periodic basis as part ofthe tree trimming and vegetation control programs. Southern Applied Technologies (SAT) has developed a high technology airborne sensing system designed to provide a cost effective method to map transmission line right-of-ways.

Range information from a laser radar can be used to rapidly converge target track files for theater missile defense from an airborne sensor platform. This paper examines the application of laser radar technology to this mission. Eyesafe lasers including carbon dioxide, holmium/thulium, and YAG shifted by optical parametric oscillators or Raman cells are considered. Performance analyses include the effects of wavelength dependent target cross sections, atmospheric attenuation and background radiation, and either direct or heterodyne detection processes on the received signal to noise ratio. Signal processing analyses include the effects of noise statistics, target fading for either direct or heterodyne detection, and the optical wavelength dependent effects of atmospheric turbulence on system false alarm and detection probabilities.

Lawrence Livermore National Laboratory developed a space-qualified high resolution (HiRes) imaging LIDAR (light detection and ranging) system for use on the DoD Clementine mission. The Clementine mission provided more than 1.7 million images of the moon, earth, and stars, including the first ever complete systematic surface mapping of the moon from the ultra-violet to near-infrared spectral regions. This article describes the Clementine HiRes/LIDAR system, discusses design goals and preliminary estimates of on-orbit performance, and summarizes lessons learned in building and using the sensor. The LIDAR receiver system consists of a HiRes imaging channel which incorporates an intensified multi-spectral visible camera combined with a laser ranging channel which uses an avalanche photo-diode for laser pulse detection and timing. The receiver was bore sighted to a lightweight McDonnell-Douglas diode-pumped Nd:YAG laser transmitter that emitted 1.06 micrometer wavelength pulses of 200 mJ/pulse and 10 ns pulse-width. The LIDAR receiver uses a common F/9.5 Cassegrain telescope assembly. The optical path of the telescope is split using a color-separating beamsplitter. The imaging channel incorporates a filter wheel assembly which spectrally selects the light which is imaged onto a custom 12 mm gated image intensifier fiber-optically coupled into a 384 multiplied by 276 pixel frame transfer CCD FPA. The image intensifier was spectrally sensitive over the 0.4 to 0.8 micrometer wavelength region. The six-position filter wheel contained 4 narrow spectral filters, one broadband and one blocking filter. At periselene (400 km) the HiRes/LIDAR imaged a 2.8 km swath width at 20-meter resolution. The LIDAR function detected differential signal return with a 40-meter range accuracy, with a maximum range capability of 640 km, limited by the bit counter in the range return counting clock. The imagery from the HiRes is most useful for smaller scale topography studies, while the LIDAR data is used for global terrain and inferred gravity maps.

Recent intelligent transportation systems (ITS) initiatives sponsored by commercial transportation companies and the U.S. Department of Transportation include an area dedicated to Automated Vehicle Control Systems (AVCS). AVCS systems are dedicated to improving passenger automobile safety, efficiency, and impact on the environment. Minimizing the number of automobile collisions through automated obstacle detection and vehicle response is vital to this effort. Simple, reliable, low cost sensors installed in automobiles to provide driver warning and/or input to vehicle systems such as braking or cruise control are the key piece to making this technology as common as air bags and seat belts. EPA emission regulations now require specific areas to periodically report the mix of vehicle types. These reports must include in the mix the 13 possible categories for vehicles. Simple low cost senors installed as part of the traffic management system will facilitate the determination of vehicle category. Laser Atlanta has recently developed two distinct types of sensors that utilize a unique multi- beam approach to detect `targets' that are potential hazards. They also provide range and range rate data to automobile control and traffic management systems.

Scannerless range imaging (SRI) is a unique approach to three dimensional imaging without scanners. SRI does, however, allow a more powerful light source to be used as compared to conventional laser radar (LADAR) systems due to the speed of operation associated with this staring system. As a result, a more efficient method of operation was investigated. As originally conceived, SRI transmits a continuous intensity modulated sinusoidal signal; however, a square wave driver is more energy efficient than a sinusoidal driver. In order to take advantage of this efficiency, a square wave operational methodology was investigated. As a result, four image frames are required for the extraction of range using a square wave to unambiguously resolve all time delays within one time period compared to a minimum of three frames for the sinusoidal wave.

Wright Laboratory and Loral Vought Systems (LVS) have been involved for the last nine years in the research and development of high power diode pumped solid state lasers for medium to long range laser radar (LADAR) seekers for tactical air-to-ground munitions. LVS provided the lead in three key LADAR programs at Wright Lab; the Submunition Guidance Program (Subguide), the Low Cost Anti-Armor Submunition Program (LOCAAS) and the Diode Laser and Detector Array Development Program (3-D). This paper discusses recent advances through the 3-D program that provide the opportunity to obtain three dimensional laser radar imagery in captive flight at a range of 5 km.

This paper treats a practical adaptation of frequency modulation (FM) radar ranging principles to an incoherent laser radar (ladar). In the simplest sense, the ladar's laser transmitter output is amplitude modulated with a radio-frequency subcarrier which itself is linearly frequency modulated. The subcarrier signal may have a start frequency in the tens to low hundreds of megahertz and stop frequency in the hundreds of megahertz to low gigahertz. The difference between the start and stop frequency, (Delta) F, is chosen to establish the desired range resolution,(Delta) R, according to usual equation from FM radar theory, (Delta) R equals c/(2(Delta) F), where c is the velocity of light. The target-reflected light is incoherently detected with a photodiode and converted into a voltage waveform. This waveform is then mixed with an undelayed sample of the original modulation waveform. The output of the mixer is processed to remove `self-clutter' that is commonly generated in FM ranging systems and obscures the true target signals. The clutter-free waveform is then processed coherently using the discrete Fourier transform to recover target amplitude and range. A breadboard of the ladar architecture was developed around a 30-mW GaAlAs diode laser operating at 830 nm. Imagery and range responses obtained show that the theoretical range resolution of 0.25 m was attained for a (Delta) F of 600 MHz. Embodiments of this ladar are likely to be practical and economical for both military and commercial applications because low-cost continuous wave laser diodes are used, coherent optical mixing is not required, and the post- mixing processor bandwidth is low.

This paper describes a light-weight, low volume, CO₂ ladar based on the multiple-folded laser (MFL). The MFL is an rf excited CO₂ waveguide laser with a unique, patented multiple folded resonator design. High resolution ladar data for selected hard targets is presented as well as MFL laser performance characteristics.

A low cost heterodyne receiver assembly has been designed and fabricated for systems such as the U.S. Army's Multiple Launch Rocket System (MLRS). The receiver assembly was fabricated from `commercial off the shelf' (COTS) components, taking advantage of the low cost of volume production for the dewar, detector, and cryogenic cooler. The design and performance of the heterodyne receiver assembly is the subject of the present paper. With minor modifications to the standard `imaging photodiode' process, heterodyne quantum efficiencies of 30% have been demonstrated at 2 GHz. While the performance achieved so far has been encouraging, further improvements in device design and processing technology can serve to enhance the performance. With these changes, we believe that heterodyne quantum efficiencies of 40% with bandwidth exceeding 3 GHz is achievable. These changes are also expected to reduce the cost of fabrication of these photodiodes.

Optimal algorithms were found for the optical signal parameters estimation in the presence of nonstationary shot noise, which was born of signals itself. The problem was solved by the way of reaching likelihood function maxima.

One of the major problems of remote sounding is determining the relations between the characteristics of echo-signals and the state of the scattering objects. In some cases the total solution of this problem in an experiment goes with unresolvable difficulties. Some very important practical results could be gotten, if experiments are being combined with mathematical and imitative simulations. A model of the processes of inverse scattering in atmospheric aerosols during sounding with pulse signal is being worked out. In the model considerations were made of the dielectric permeability, form and orientation peculiarities of the scatterers, their size-distribution, wind and turbulent pulsation characteristics, movement effects of the locator, and the beam-scanning effects. One of the peculiarities of the approach used in the model is separating the scattering volume not only into series of physical separate parts but also into series of partial components that are obliged to different groups of scatterers' sizes. The research done through imitative and statistical modeling allowed us to know the statistical characteristics of the echo-signals with respect to turbulent intensity. The received data agree with experimental results. They can be used in many practical applications. 11

This paper summarizes test results of the Helicopter Laser Radar (HLR) System which has been developed at Fibertek, Inc. The HLR program is under the direction of the U.S. Army Night Vision and Electronic Sensors Directorate, Air Systems Division, as part of the Army Helicopter Obstacle Avoidance System (OASYS) program. The HLR system is a direct detection laser radar system using a diode-pumped solid-state laser operating at 1.54 micrometer. A diode-pumped system offers small size, robust range performance, small output aperture, and a short pulse length for high range resolution. The output wavelength was chosen for extended eyesafety limits and covertness.