Researchers have long recognized that robust solutions to many difficult image analysis tasks might be achieved if image data could be acquired as range mapped (3-D) representations of the scene. Research published as early as 1976 reported the demonstration of a range mapping imager based on laser radar. Perceptron has recently developed a commercially practical scanning laser radar capable of rapid acquisition of range mapped images. This technology has been applied to the development of an autonomous robotic bin picking work cell. The work cell and the laser radar system are described. Additional current applications of the scanning laser radar are also mentioned.

A scannerless laser detection and ranging (LADAR) system is presently in development for applications at Sandia National Laboratories. This LADAR design eliminates the need for a mechanical laser beam scanner which is often the system component that limits the use of laser radars for many applications. Range to the target scene is determined in this approach by measuring the phase shift of the intensity modulation on the received optical return compared to the reference. The approach used in this LADAR is unique because the method used to detect this phase shift is an array of time integrating detectors that also records the image of the target scene. An analytical model is presented that describes the LADAR system performance. Applications of this LADAR system also are reviewed. They include terminal guidance of advanced conventional munitions, perimeter surveillance of secure facilities, mapping potholes/cracks in the U.S. highway system for improved maintenance scheduling, active collision avoidance of commercial/private vehicles, robotic vision integrated into advanced manufacturing concepts, and a novel airborne multi-sensor system containing LADAR, SAR, and LIDAR to locate and measure the thickness of ocean oil spills.

Performance projections based on the analytical model of a scannerless laser radar system (presented in a companion paper) are compared to laboratory simulations and to field data measurements. Data and characteristics of the system, including camera response, image spatial resolution, and contributions to the signal-to-noise ratio are presented. A discussion of range resolution for this system also is presented, and finally, the performance characteristics of the prototype benchtop system are summarized.

There exists a need for a low-cost aircraft collision-avoidance system suitable, and affordable, for general aviation use. The fact that most of all of mid-air collisions occur under high visibility conditions, and many in and near terminal airspace, allows the consideration of optical means such as a LIDAR system for ranging and tracking to other aircraft to determine if a collision threat exists. This paper presents a system parametric analysis and discusses the LIDAR design tradeoffs with consideration of atmospheric attention, false target discrimination, threat scenario, scanning dynamics, wide FOV retroreflector array performance, and sizing for airframe ease of mounting and minimal aerodynamic effects. Further, concepts for the optical design and mechanization of the scanner are presented as well as a pilot warning/display means for evasive maneuver consideration.

An internal research and development program at Teledyne Brown Engineering has produced a laser radar device to measure velocities of projectiles as they travel through the barrel of a gun. The technique measures velocities directly via the Doppler shift imposed on a retro- reflected laser beam. The device, called the In-Bore Chronograph (IBC), is believed to be the first coherent laser radar to be offered commercially. The IBC measures in-bore velocities from 5 to 2500 m/sec.

Vibration signatures of the Low Power Atmospheric Compensation Experiment (LACE) satellite were obtained using a ground based CO₂ laser radar. The laser radar operated in a cw mode and utilized autodyne receivers to extract relative target velocity information between a germanium retroreflector located at the base of the satellite and a retroreflector array located at the tip of an extended forward boom. Time-frequency analysis algorithms were applied to the vibration data to investigate the correlation between excitations and modal structure. The resultant analysis suggests that vibration modes of an on-orbit space craft can be suppressed using simple open-loop techniques.

Our paper presents a new optical distance sensor, which can be used in applications. The sensor measures the time interval between the emission of a modulated laser signal and the detection of a small fraction of the signal reflected from the measured object. Maximum likelihood optimization of the transmitted signal and the structure of the receiver lead to a pseudo noise (PN) signal, which modulates a cw diode laser in conjunction with a delay locked loop (DLL) receiver. The measured distance is determined from the zero crossing of the crosscorrelation of the received and the transmitted signal. The variation of time delay is realized by means of the variation of the frequency of the voltage controlled oscillator (VCO), which provides the clock signal for the PN-generator. The VCO frequency is inversely proportional to the distance to be measured so that the spatial resolution is directly proportional to the distance. The theoretical results are verified by means of more detailed numerical simulations. The simulations were also used for the optimization of the whole system as well as the particular subsystems. Results of measurements demonstrate the practical feasibility of the system.

Laser vibration sensing has traditionally relied on the use of limiters and frequency modulation (FM) discriminators to process frequency modulated laser radar returns. The performance of the traditional FM discriminator approach can be limited by laser radar target characteristics and motion (speckle noise) and laser temporal coherence. In this paper we examine a novel laser vibration signal processor, a spectrogram processor, and compare its performance with the traditional limiter/FM discriminator signal processor used to process laser radar vibration measurements. The two processes are also compared using some laser radar measurement data.

A time-frequency distribution (TFD) signal processor, developed at the Applied Physics Laboratory, is currently under evaluation using simulated signals and actual laser vibration sensor (LVS) data that we collected on various ship targets. Preliminary results for one instantaneous frequency (IF) estimator implementation, the smoothed cross Wigner-Ville Distribution (XWVD), indicate 8 to 10 dB demodulation (CNR) advantage compared to a digital FM limiter-discriminator. A second approach, using the unsmoothed XWVD TFD, demonstrated a 3-5 dB advantage. Regarding spectral estimation, we are investigating performance of our reduced interference distribution (RID) implementation through comparison with the short-time Fourier transform (STFT). From the LVS data processed, indications are that a significant increase in spectral and temporal resolution exists using our RID approach. Our processor also provided improved detectability over the STFT for transient signals and short-lived sinusoids. Significant correlation between accepted acoustic lines and LVS-derived vibration lines are indicated. Details are presented that describe our signal simulation, the LVS measurements, and signal processing implementations along with assumptions based on measured speckle-induced amplitude modulation.

an acousto-optic signal processor (AOSP) has been developed for use with laser-based velocity measurement instruments. It has been demonstrated with Doppler laser radar and laser velocimeter systems. Due to its inherent ability to display information about its entire spectral range without post-processing of data, the AOSP is deemed to be superior to conventional spectrum analyzers for some applications.

A concept for integrating the airborne sensing capabilities of synthetic aperture radar (SAR) with laser detection and ranging (LADAR) for terminal guidance is presented. The advantages of each technology in the reconnaissance and terminal guidance roles for target acquisition are exploited. The concept is directed at terminal guidance against fixed and quasi-fixed targets (i.e., targets expected to be in approximately the same location and orientation from the time of reconnaissance to the time of targeting). The advantages of airborne SAR are high resolution, all-weather, standoff reconnaissance capabilities. The advantages of LADAR are high resolution in the real aperture mode using moderately sized and priced optics, and good performance over modest ranges (on the order of a kilometer or less). Within the concept, LADAR would provide terminal guidance using two SAR provided data sets: (1) target estimated coordinates, and (2) the SAR imagery of target/surround. Technical risks are: lack of a demonstrated capability for SAR-to-LADAR image correlation; lack of analysis of low- cost, light weight LADAR and real-time correlators; and lack of analysis of adequate signal- to-noise in a range of atmospheric environments. This paper is directed at the use of SAR image by the LADAR for aim point refinement. It addresses geometric differences in the SAR and LADAR images, the effect of different reflectances on scene segmentation, and the basis for an approach for developing common geometric projections for the SAR and LADAR image correlations.

The speckle bandwidth in a CO₂ laser radar return is measured by applying a tilt motion to a diffuse target which is also driven with a piston motion by a loudspeaker. The speckle bandwidth vs. tilt frequency is reported. The frequency and amplitude characteristics of a glint target undergoing piston motion only are also described.

A generalized model for the calculation of heterodyne efficiency has been developed. The model permits the calculation of the mixing efficiency for arbitrary amplitude profiles, wave front descriptions, and angles of incidence. The model is used to calculate the heterodyne efficiency of a CO₂ coherent laser radar as a function of amplitude profile, image translation, wave front tilt and curvature. Analytical results are used to develop a concise set of selection rules for coherent laser radars.

This paper summarizes progress toward developing coherent ladar technology using arrays of subapertures for coping with target-induced speckle which can reduce the carrier-to-noise ratio for ladar systems. We have selected an optimum receiver design, developed algorithms for determining how to co-phase the IF signals from the different sub-apertures/receivers, and have begun to test these on a two-aperture, coherent 1064 nm ladar. Computer simulations of the ladar are being developed including partially developed speckle effects from the target. Target speckle has been measured from different materials and at two different wavelengths for bench-marking the computer simulations. We have measured and are developing the theory for the time-dependent optical phase shifts observed from a rough, rotating target. The signal enhancement has been calculated that might be expected for a rough target illuminated by a coherent, 1064 nm laser. Finally, we have designed and are beginning to implement an experiment to show that imaging through a turbulent medium can be achieved.

We investigated a space diversity optical heterodyne array receiver for optimal coherent detection of finite transverse coherence length fields. In such an array receiver, each of the independent IF signals are appropriately phase-shifted and summed to generate a single IF signal with improved statistical qualities. In this paper we show that the advantages offered by a coherent array are both an increased average carrier-to-noise ratio and a reduction in carrier fading. We also show that the equal gain diversity reception technique performs almost as well as the maximal ratio technique with significantly less hardware complexity. Finally, we present the experimental results from a two element, one micron, laboratory breadboard ladar system.

A theoretical model is presented for the mutual coherence function that describes the power spectrum of the intermediate frequency (IF) signal resulting from coherent laser radar detection of a fully illuminated rough rotating cylinder. Preliminary calculations for the correlation length and bandwidths of the coherently detected dynamic speckle fields show that Doppler effects on speckle dynamics are on the same order of magnitude as speckle translation effects, and that scatterer exchange effects are negligible. We show that for a fully diffuse object, the shape of the spectrum (and autocorrelation function) is Gaussian. The spectrum appears to be the sum of two Gaussian functions when the scattering object has a near-specular component, one due to the specularly reflected field and the other due to the diffusely reflected field. While the IF BW of the signal resulting from the diffusely scattered field depends upon the cylinder's radius, the IF BW of the specularly reflected field depends upon the width of a window function, which is wavelength dependent.

A model dust distribution over the lunar terminator region, based on instrument measurements and observations by Apollo astronauts, is used to assess the feasibility of detecting and mapping the dust distribution with a lunar-based lidar instrument. We assume a refractive index appropriate to volcanic dust, and use Mie scattering formalism along with the model dust distribution to determine the expected lidar backscatter coefficient as a function of range cell location. Requirements for peak transmitter power, pulse length, and pulse repetition rate are examined. This analysis is carried out both for a lunar surface instrument package and for a lunar orbiting instrument. Orbital instrument requirements are analyzed for orbital altitudes of 60, 80, and 100 km above the lunar surface. Expected signal-to-noise ratios and additional performance parameters are presented for these candidate lidar systems. Size and power requirements for the instruments are also discussed.

A ground-based lidar facility, which has been in operation at the NASA Langley Research Center since 1974, has been substantially upgraded with state-of-the-art technology, including 12-bit CAMAC based digitizers and a 386 computer with a laser printer and optical disk drive. An Nd:YAG laser was added to the system to provide wavelengths at 1064 nm and 532 nm. A new detector package was added to accommodate the ruby 649 nm and the YAG 532 nm wavelengths with provisions to add a detector for 1064 nm later. Photon counting at 532 nm is also possible with the addition of the new detector package and a cooled photomultiplier tube. Backscatter measurements from the stratospheric aerosol cloud, produced by the 1991 eruption of Mount Pinatubo, have been obtained with the system operating in the analog mode at 694 nm. Regular measurements, approximately weekly, were made over a period of a year and a half after the eruption. The results indicate a continuous aerosol increase, with multi-layered structure, over the measurement site for the first eight months following the eruption, after which the aerosol loading started decreasing and has continued, but the aerosol backscatter a year and a half after the eruption was still substantially above the pre-Pinatubo levels.

Development of a wavelength-stabilized laser diode injection-seeded alexandrite laser for differential absorption lidar (DIAL) measurements of atmospheric water vapor in the 727 nm region is described.

In this paper, we summarize the design and preliminary performance evaluation of a new raster-scanning BAGI imager that is intended for long-range operation, at a target range of 300 m. A system capable of imaging at this range is desired to make airborne gas imaging from a low-flying airplane or helicopter possible. The system uses a 20 W CO₂ laser and a redesigned scanner that employs telescopic transmission and receiving optics. Model predictions of the performance of the new system and some recent field testing results are presented. Issues relating to gas imaging at long ranges are also discussed.

It has been theoretically shown that vertical distribution of sea water scattering coefficient b(z) can be derived from temporal dependence of backscattered pulse polarization degree when sounding sea water by linear polarized light pulses. Experimental examination of the theoretical method has been carried out by using airborne lidar receiving two orthogonal polarized components of backscattered pulse. Measurements of the lidar signals are accompanied by shipboard measurements of the vertical distribution of the sea water attenuation coefficient c(z). Obtained data show that the backscattered pulse depolarization degree is small and doesn't exceed 6 - 8% at the time interval until 150 ns. The comparison of theoretical calculations and experimental results concerning depolarization degree allow us to evaluate the important parameter of sea water Mueller matrix- `depolarization factor' describing the difference between the first and second diagonal elements of the scattering matrix.

Results of preliminary measurements of aerosol concentrations and fluxes in the coastal zone above Gdansk Bay are presented. The measurements were carried out by means of the lidar system FLS-12 from the coast of South Baltic in Sopot and Hel, from June to November 1992. Using lidar data the authors calculated height profiles of particle concentrations. Also, the influence of wind speed on particle fluxes and total particle mass were investigated.

A discussion of the multifrequency lidar inverse problem in aerosol research is given. Two models of marigenic aerosol are described for water and water/salt aerosol ensembles. The Tikhonov functional solution method of the inverse problem for both models is described. The algorithms for calculating the values of the scattering medium optical parameters and the size- distribution functions of the aerosol are discussed. The numerical simulations done to test the inverse problem solution algorithms are described and a short discussion of the results is given.