Active Infra-Red (IR) systems developed in the past ten years are now available for missile defense applications. The main purpose of this paper is to describe the advantages an active IR system could offer to a ballistic missile defense (BMD). The active IR system considered in this paper is a LIDAR (LIght Detection And Ranging) system. Historically, the Lincoln Laboratory in the USA began using lasers in the early 1960's. The initial applications included the development of a LIDAR system enabling the measurement of the distance between the earth and the moon in 1962. Satellite tracking using LIDAR began early in 1973. Today, technological developments, with the miniaturization of systems and increased performance levels, have enabled new ambitious projects such as the Discrimination Interceptor Technology Program (DITP) program started in 1998 and the use of LIDAR to help in the discrimination of future exo-atmospheric interceptors within the framework of BMD. The first part of this paper presents the possible contribution of LIDAR to BMD: the main roles, objectives, and strategic advantages. The second part gives a brief overview of the technological features of a generic LIDAR instrument, rapidly addressing laser sources, detectors, optics and electronics. Finally, a modeling of an IR LIDAR system, limited solely to direct detection, and an estimation of performance levels will be presented. A list of possible IR active discriminators will be then presented on the basis of the previous analysis and proposed as new constraints in the design of discrete objects.

The construction of 3D models from light detection and ranging (LIDAR) data requires reliable and accurate alignment of multiple overlapping scans. While established manual and automated 3D alignment methods generally perform well, aligning scans of complex scenes from arbitrary perspectives with small amounts of overlap remains challenging. The projection information available with scanned LIDAR data is generally underutilized and may be better exploited to simplify the alignment process, avoiding manually specified algorithm parameters and improving reliability. In this work, we present projective methods for manual and automated 3D alignment and introduce a projective measure of surface interpenetration to quantify alignment error. Performance is demonstrated with a combination of indoor and outdoor scan sets, including cluttered forest scenes, and compared to results obtained using an established commercial product.

A 2-μm wavelength coherent Doppler lidar system under development at NASA Langley Research Center in Virginia is discussed from the perspective of signal processing. The current data processing algorithm returns a variety of wind parameters such as power spectra, Doppler shift, wind speed, and wind direction. This paper compares the quality of selected wind parameter estimates by computing the power spectral density of stochastic lidar return data via the periodogram and the maximum likelihood power estimation method. The improvement in resolution of power spectra and Doppler shift estimates is witnessed by means of zero padding before the power spectral density was estimated in each range bin.

The wind parameter estimates from a state-of-the-art 2-μm coherent lidar system located at NASA Langley, Virginia, named VALIDAR (validation lidar), were compared after normalizing the noise by its estimated power spectra via the periodogram and the linear predictive coding (LPC) scheme. The power spectra and the Doppler shift estimates were the main parameter estimates for comparison. Different types of windowing functions were implemented in VALIDAR data processing algorithm and their impact on the wind parameter estimates was observed. Time and frequency independent windowing functions such as Rectangular, Hanning, and Kaiser-Bessel and time and frequency dependent apodized windowing function were compared. The briefing of current nonlinear algorithm development for Doppler shift correction subsequently follows.

In this paper a knowledge base driven technique is presented to detect targets based on the geometric properties of the "shadows" cast by the targets in laser radar (LADAR) range images. The geometric properties of the shadows are relatively easy to compute and are less susceptible to target obscuration. In this technique synthetic images of targets are utilized to populate the knowledge base. The validity of the approach is demonstrated by detecting an armed personnel carrier and a tank utilizing data from captive flight tests.

EADS Germany is the world market leader in commercial Helicopter Laser Radar (HELLAS) Obstacle Warning Systems. The HELLAS-Warning System has been introduced into the market in 2000, is in service at German Border Control (Bundespolizei) and Royal Thai Airforce and is successfully evaluated by the Foreign Comparative Test Program (FCT) of the USSOCOM. Currently the successor system HELLAS-Awareness is in development. It will have extended sensor performance, enhanced realtime data processing capabilities and advanced HMI features. We will give an outline of the new sensor unit concerning detection technology and helicopter integration aspects. The system provides a widespread field of view with additional dynamic line of sight steering and a large detection range in combination with a high frame rate of 3Hz. The workflow of the data processing will be presented with focus on novel filter techniques and obstacle classification methods. As commonly known the former are indispensable due to unavoidable statistical measuring errors and solarisation. The amount of information in the filtered raw data is further reduced by ground segmentation. The remaining raised objects are extracted and classified in several stages into different obstacle classes. We will show the prioritization function which orders the obstacles concerning to their threat potential to the helicopter taking into account the actual flight dynamics. The priority of an object determines the display and provision of warnings to the pilot. Possible HMI representation includes video or FLIR overlay on multifunction displays, audio warnings and visualization of information on helmet mounted displays and digital maps. Different concepts will be presented.

Although laser ranging and scanning sensors are widely used in a variety of industries, a sensor designed for spacecraft operations, including autonomous rendezvous, inspection and servicing remains a challenge. This is primarily due to critical requirements, including the need to have simultaneous high sampling speed, and good range and lateral resolution at both short range of a few meters and at long range of a few hundred meters. A typical LIDAR sensor is not suitable for tracking at the close-in distance, just before rendezvous, or during a critical close-up inspection, since its range resolution is in the tens of millimeters and can only be improved by averaging at the expense of speed. A laser triangulation sensor is capable of simultaneously having both high range resolution (~1mm) and high speed (~10kHz) at short distance. But the range resolution of a triangulation sensor reduces rapidly as range increases, its performance is inferior compared to a LIDAR based sensor at long range. NEPTEC TriDAR (triangulation + LIDAR) is a hybrid sensor that combines a triangulation sensor and a TOF sensor for spacecraft autonomous rendezvous and inspection. It has been developed in part from technology used in NEPTEC's OBSS (Orbiter Boom Sensor System) 3D laser camera. The OBSS LCS was used for inspection of the Shuttle tiles on STS-114. In this paper, the TriDAR design that combines triangulation and LIDAR to produce high speed and high resolution for both short and long range is described. To successfully produce this sensor for space, an athermalized optical steering system shared by the two sensors has been developed. Results from performance testing of a prototype, designed for autonomous rendezvous, are given.

Lidar has been used to track the downwind dispersion of rocket launch contrails and also to determine the particle size distribution of the primary Al₂O₃ smoke particles in the contrail. However, the determination of primary particle size from such lidar measurements is complicated by the presence of secondary smoke in the contrail composed of aqueous hydrochloric acid droplets. In addition, the secondary smoke tends to condense upon the Al₂O₃ primary smoke particles in the form of a liquid coating, with the primary smoke particles acting as condensation nuclei. The potential effect of this liquid coating upon the lidar backscatter return from the rocket contrail is estimated using a standard light scattering model (BHCOAT) for two-zone core-mantle particles.

Through the utilization of scanning MEMS mirrors in ladar devices, a whole new range of potential military, Homeland Security, law enforcement, and civilian applications is now possible. Currently, ladar devices are typically large (>15,000 cc), heavy (>15 kg), and expensive (>$100,000) while current MEMS ladar designs are more than a magnitude less, opening up a myriad of potential new applications. One such application with current technology is a GPS integrated MEMS ladar unit, which could be used for real-time border monitoring or the creation of virtual 3D battlefields after being dropped or propelled into hostile territory. Another current technology that can be integrated into a MEMS ladar unit is digital video that can give high resolution and true color to a picture that is then enhanced with range information in a real-time display format that is easier for the user to understand and assimilate than typical gray-scale or false color images. The problem with using 2-axis MEMS mirrors in ladar devices is that in order to have a resonance frequency capable of practical real-time scanning, they must either be quite small and/or have a low maximum tilt angle. Typically, this value has been less than (< or = to 10 mg-mm²-kHz²)-degrees. We have been able to solve this problem by using angle amplification techniques that utilize a series of MEMS mirrors and/or a specialized set of optics to achieve a broad field of view. These techniques and some of their novel applications mentioned will be explained and discussed herein.

Gas monitoring over long distances using Frequency Modulation (FM) spectroscopy require phase insensitive detection scheme because of the severe scintillation problem. We report our effort to develop a long working distance CO2 monitoring LIDAR that uses phase insensitive Two-Tone Frequency Modulation (TTFM) spectroscopy technique. We could detect 10^-4 single pass absorption, and could detect 1ppm CO2 level change in normal air.

Rapid and efficient detection of surface mines, IED's (Improvised Explosive Devices) and UXO (Unexploded Ordnance) is of high priority in military conflicts. High range resolution laser radars combined with passive hyper/multispectral sensors offer an interesting concept to help solving this problem. This paper reports on laser radar data collection of various surface mines in different types of terrain. In order to evaluate the capability of 3D imaging for detecting and classifying the objects of interest a scanning laser radar was used to scan mines and surrounding terrain with high angular and range resolution. These data were then fed into a laser radar model capable of generating range waveforms for a variety of system parameters and combinations of different targets and backgrounds. We can thus simulate a potential system by down sampling to relevant pixel sizes and laser/receiver characteristics. Data, simulations and examples will be presented.

In this paper, a number of techniques for segmentation and classification of airborne laser scanner data are presented. First, a method for ground estimation is described, that is based on region growing starting from a set of ground seed points. In order to prevent misclassification of buildings and vegetation as ground, a number of non-ground regions are first extracted, in which seed points should be discarded. Then, a decision-level fusion approach for building detection is proposed, in which the outputs of different classifiers are combined in order to improve the final classification results. Finally, a technique for building reconstruction is briefly outlined. In addition to being a tool for creating 3D building models, it also serves as a final step in the building classification process since it excludes regions not belonging to any roof segment in the final building model.

Advanced optical fuze (OF) technology based on high-performance optoelectronic sensor is developed for munitions applications. The compact and robust design of the OF employed high-power vertical-cavity surface-emitting lasers (VCSELs), the metal-semiconductor-metal photodetectors, SiGe ASIC driver, miniature optics, and the corresponding electronic signal processors. Mounted on the front of the projectile, the laser transmitter sends out a highly collimated beam that is amplitude modulated with a chirped RF signal. The reflected optical signal from the target is picked up by the photoreceiver on the projectile which also has its electrical bias modulated at the same time-dependent operational frequency as the transmitted optical signal. The on-board signal processor heterodynes both transmitted and the delayed optical waveforms and generates an intermediate frequency corresponding to the time delay due to the travel time of the light. Further measurement of the mixed signals yields directly the range information of the target.

We describe all solid state differential absorption lidar (DIAL) based on the mid-infrared (IR) tunable Optical Parametric Oscillator (OPO). Generation of tunable mid-infrared laser radiation using a two stage tandem OPO was demonstrated. The first stage was based on the nonlinear KTP crystal and produced up to 45 mJ of 1.57 μm radiation, while pumped by a commercial Q-switched Nd:YAG laser. The quality of signal beam was improved by the use of unstable resonator. The AgGaSe₂ crystal was used in the second stage OPO. Idler energies up to 1 mJ were generated at this stage within tuning range from 6 to 12 μm. The receiver consisted of a 250 mm gold mirror telescope, two channel detection system and control electronics. We have designed a photoacoustic cell for wavelength calibration of lidar. Preliminary lidar field test results are presented.

This paper presents the status of an indoor artifact-based Performance Evaluation Facility at the National Institute of Standards and Technology (NIST) for 3D imaging systems, a terminology pre-standard, and a summary of the ranging protocol pre-standard. The indoor facility will be used to develop test protocols and performance metrics for the evaluation of terrestrial 3D imaging systems. The NIST facility was initiated in response to a workshop which was held at NIST in 2003 to determine future efforts needed to standardize 3D imaging system testing and reporting and to assess the need for a neutral performance evaluation facility. Three additional workshops have since been held at NIST with the most recent on March 2-3, 2006. These workshops provided further guidance in defining priorities and in identifying the types of measurements that are of most interest to the terrestrial scanning community. The two pre-standards were developed based on feedback from the workshops.

Employing a modified photon mapping technique that originated within the computer graphics community, a first-principle based elastic LIDAR model was developed within the Digital and Remote Sensing Image Generation (DIRSIG) framework that calculates time-gated photon counts at a sensor from topographic reflections and multiply scattered returns. The LIDAR module handles a wide variety of complicated scene geometries, diverse surface and participating media optical characteristics, multiple bounce and multiple scattering effects, and a variety of source and sensor models. This flexible modeling environment allows the researcher to evaluate sensor design trades for topographic systems and the impact that scattering constituents (e.g. water vapor, dust, sediment, soot, etc.) could have on a Differential Absorption LIDAR (DIAL) system's ability to detect and quantify constituents of interest within volumes including water and atmospheric plumes. This paper will present the numerical approaches employed to predict sensor reaching photon counts including specific approaches adopted to model multiple scattering and absorption within a plume. These approaches will be discussed and benchmarked against analytically predicted results using a non-stationary, diffusion approximation and a multiple scattering LIDAR equation. The analytical development and consistency of the modified photon mapping method with the underlying physics and radiative transfer theory for participating media is also presented. A representative dataset generated by DIRSIG of a DIAL system will be presented and analyzed for a synthetic scene containing a factory stack plume containing absorption and scattering effluents.

32×32 element InGaAsP/InP avalanche photodiode arrays operating at 1.06 μm have been fabricated and characterized. Material characterization data on uniformity and layer quality have been correlated to array performance using the McIntyre model. Sheet resistivity maps, Hall mobility, dark current, capacitance and gain data are presented. These devices have showed gain as high as 75 with low dark current. Both device and materials uniformity characterization data will be presented.

The Digital Imaging and Remote Sensing Image Generation (DIRSIG) model is an established, first-principles based scene simulation tool that produces synthetic multispectral and hyperspectral images from the visible to long wave infrared (0.4 to 20 microns). Over the last few years, significant enhancements such as spectral polarimetric and active Light Detection and Ranging (LIDAR) models have also been incorporated into the software, providing an extremely powerful tool for algorithm testing and sensor evaluation. However, the extensive time required to create large-scale scenes has limited DIRSIG's ability to generate scenes "on demand." To date, scene generation has been a laborious, time-intensive process, as the terrain model, CAD objects and background maps have to be created and attributed manually. To shorten the time required for this process, we are initiating a research effort that aims to reduce the man-in-the-loop requirements for several aspects of synthetic hyperspectral scene construction. Through a fusion of 3D LIDAR data with passive imagery, we are working to semi-automate several of the required tasks in the DIRSIG scene creation process. Additionally, many of the remaining tasks will also realize a shortened implementation time through this application of multi-modal imagery. This paper reports on the progress made thus far in achieving these objectives.

We report on the design, construction and operation of a new multiwavelength lidar developed for the Agricultural Research Service of the United States Department of Agriculture and its program on particle emissions from animal production facilities. The lidar incorporates a laser emitting simultaneous, pulsed Nd laser radiation at 355, 532 and 1064 nm at a PRF of 10 kHz. Lidar backscatter and extinction data are modeled to extract the aerosol information. All-reflective optics combined with dichroic and interferometric filters permit all the wavelength channels to be measured simultaneously, day or night, using photon counting by PMTs, an APD, and high speed scaling. The lidar is housed in a transportable trailer for all-weather operation at any accessible site. The laser beams are directed in both azimuth and elevation to targets of interest. We describe application of the lidar in a multidisciplinary atmospheric study at a swine production farm in Iowa. Aerosol plumes emitted from the hog barns were prominent phenomena, and their variations with temperature, turbulence, stability and feed cycle were studied, using arrays of particle samplers and turbulence detectors. Other lidar measurements focused on air motion as seen by long duration scans of the farm region. Successful operation of this lidar confirms the value of multiwavelength, eye-safe lidars for agricultural aerosol measurements.

USU LadarSIM Release 2.0 is a ladar simulator that has the ability to feed high-level mission scripts into a processor that automatically generates scan commands during flight simulations. The scan generation depends on specified flight trajectories and scenes consisting of terrain and targets. The scenes and trajectories can either consist of simulated or actual data. The first modeling step produces an outline of scan footprints in xyz space. Once mission goals have been analyzed and it is determined that the scan footprints are appropriately distributed or placed, specific scans can then be chosen for the generation of complete radiometry-based range images and point clouds. The simulation is capable of quickly modeling ray-trace geometry associated with (1) various focal plane arrays and scanner configurations and (2) various scene and trajectories associated with particular maneuvers or missions.

This paper presents a generic simulation model for a ladar scanner with up to three scan elements, each having a steering, stabilization and/or pattern-scanning role. Of interest is the development of algorithms that automatically generate commands to the scan elements given beam-steering objectives out of the ladar aperture, and the base motion of the sensor platform. First, a straight-forward single-element body-fixed beam-steering methodology is presented. Then a unique multi-element redirective and reflective space-fixed beam-steering methodology is explained. It is shown that standard direction cosine matrix decomposition methods fail when using two orthogonal, space-fixed rotations, thus demanding the development of a new algorithm for beam steering. Finally, a related steering control methodology is presented that uses two separate optical elements mathematically combined to determine the necessary scan element commands. Limits, restrictions, and results on this methodology are presented.

Ladar systems are an emerging technology with applications in many fields. Consequently, simulations for these systems have become a valuable tool in the improvement of existing systems and the development of new ones. This paper discusses the theory and issues involved in reliably modeling the return waveform of a ladar beam footprint in the Utah State University LadarSIM simulation software. Emphasis is placed on modeling system-level effects that allow an investigation of engineering tradeoffs in preliminary designs, and validation of behaviors in fabricated designs. Efforts have been made to decrease the necessary computation time while still maintaining a usable model. A full waveform simulation is implemented that models optical signals received on detector followed by electronic signals and discriminators commonly encountered in contemporary direct-detection ladar systems. Waveforms are modeled using a novel hexagonal sampling process applied across the ladar beam footprint. Each sample is weighted using a Gaussian spatial profile for a well formed laser footprint. Model fidelity is also improved by using a bidirectional reflectance distribution function (BRDF) for target reflectance. Once photons are converted to electrons, waveform processing is used to detect first, last or multiple return pulses. The detection methods discussed in this paper are a threshold detection method, a constant fraction method, and a derivative zero-crossing method. Various detection phenomena, such as range error, walk error, drop outs and false alarms, can be studied using these detection methods.

Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges. Since IRST systems cannot measure range and line-of-sight velocity, they have difficulty distinguishing missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a chirped amplitude modulation ladar to provide range and velocity measurements for tracking of targets handed over to it by the distributed aperture system IRST (DAS-IRST) under development at the Naval Research Laboratory (NRL) under Office of Naval Research (ONR) sponsorship. By using an array receiver based on Intevac Inc.'s Electron Bombarded Active Pixel Sensor (EBAPS) operating near 1.5 μm wavelength, ARL's ladar also provides 3D imagery of potential threats in support of the force protection mission. In Phase I, ARL designed and built a breadboard ladar system for proof-of-principle static platform field tests. In Phase II, ARL is improving the ladar system to process and display 3D imagery and range-Doppler plots in near real-time, to re-register frames in near real-time to compensate for platform and target lateral motions during data acquisition, and to operate with better quality EBAPS tubes with higher quantum efficiency and better response spatial uniformity. The chirped AM ladar theory, breadboard design, performance model results, and initial breadboard preliminary test results were presented last year at this conference. This paper presents the results of tests at the Navy's Chesapeake Bay Detachment facility. The improvements to the ladar breadboard since last year are also presented.

In ARL's current chirped amplitude modulation (AM) ladar prototypes using unity gain solid state detectors, amplifier noise limits the receiver sensitivity. This noise is well above the signal shot noise limit. We are developing a method using Geiger-mode avalanche photodiode (Gm-APD) photon counting detectors in the chirped AM ladar receiver to yield sensitivities approaching the signal shot noise limit. This method is based on the fact that the chirped AM waveform that modulates the transmitted laser power also modulates the average photon arrival rate at the receiver with a delay corresponding to the round-trip time between the transceiver and the target. We present the concept, and computer and electronic simulation results for ARL's chirped AM ladar operating with a photon counting receiver. We also present the design and initial results of the proof-of-principle laboratory optical experiment that we recently performed. The simulation and experimental results predict significant improvements in the ladar's receiver sensitivity.

The Active Range of the Optical Systems Test Facility was established in 2003 to allow for rapid development and demonstration of active electro-optic technology in a system context, investigate critical phenomenology issues in a repeatable environment, and enhance expertise in electro-optic technology. The test facility consists of four major parts: a control room, a 50-m range with installed ladar systems, a far-field emulator comprising of a 1-m primary mirror and zoom optics, and a dynamic target manipulator for full-scale (1-m) targets. This paper will focus on the capabilities of the Optical Systems Test Facility and present some examples of laser radar experiments and data taken in the range.

We present an improved method for estimating the dark count rate of single-photon-sensitive avalanche photodiodes (SPADs) with either InP or InAlAs multiplication layers. Our simulation of junction breakdown probability can easily accommodate arbitrary electric field profiles and APD bias conditions. In combination with local models of dark carrier generation, our technique can provide more realistic estimates of dark count rate than are obtained by multiplying the primary dark current by a single junction breakdown probability, or by assuming constant electric fields in the multiplication layer. Our method can assist in the design of SPADs for demanding laser radar applications.

NASA is developing state-of-the-art, all-solid-state, conductively cooled, diode-pumped, single longitudinal mode, tunable, short-pulsed, and high energy UV transmitters for ozone sensing measurements based on the Differential Absorption Lidar (DIAL) technique. The goal is to demonstrate output pulse energies greater than 200 mJ at pulse repetition frequencies of 10 Hz to 50 Hz, and pulsewidths in the range of 10 ns to 25 ns at UV wavelengths of 308 nm to 320 nm. The proposed scheme is to utilize the robust Nd:YAG pump laser technology in combination with nonlinear optics arrangement comprising of a novel optical parametric oscillator (OPO) and a sum frequency generator (SFG) to generate required UV wavelengths. In this paper, recent results of the development of Nd:YAG pump laser and UV converter module are presented. At 1064 nm, an output pulse energy of 1020 mJ at 16 ns pulsewidth and 50 Hz PRF yielding greater than 7% wall plug efficiency has been demonstrated. With improved drive electronics, this pump laser has the potential to generate greater than 1.2 J/pulse. The refined OPO module to aid in the generation of >200 mJ/pulse of UV radiation is also presented. The UV transmitters are being designed for DIAL operation under strong daylight conditions from space based platforms.

Applications of a laser radar system with depth accuracy down to 0.2 mm for high accuracy 3-D imaging are described. The system is based on a green pulsed laser triggering a picosecond ICCD camera with data recording of only a few seconds. The submillimeter accuracy gradually degrades at ranges above a few hundred meters due to turbulence, vibrations, etc. As a specific example, we show 3-D accuracy for surface tile inspection of a miniature space shuttle and the resolution of cracks and defects is demonstrated, which is relevant for the planned laser radar inspections from the space shuttle boom and the longer range survey from the International Space Station. By coupling the laser light through a Raman fiber we also demonstrate multispectral 3-D imaging.

High range-resolution active imaging requires high-bandwidth transmitters and receivers. At Lockheed Martin Coherent Technologies (LMCT), we are developing both linear Frequency Modulated Continuous Wave (FMCW) and short pulse laser radar sensors to supply the needed bandwidth. FMCW waveforms are advantageous in many applications, since target returns can be optically demodulated, mitigating the need for high-speed detectors and receiver electronics, enabling the use of much lower bandwidth cameras. However, some of the penalties paid for these transceivers include a finite range search interval (RSI) and the requirement for slow chirp or long-duration waveforms, owing to the relatively slow sample frequency of the cameras used in the receiver. For applications requiring larger RSI's and short duration waveforms, LMCT is also developing high bandwidth pulsed ladar waveforms and receivers. This paper will include discussion of these two methods, their tradeoffs and sample imagery collected at LMCT.