This PDF file contains the front matter associated with SPIE Proceedings Volume 8037, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

An active imaging system using UV fluorescence for target discrimination is proposed. The emission wavelength is characteristic of the target material and allows spectral discrimination of targets from clutter. The burst-illumination-LIDAR system transmits a laser pulse and the fluorescent return is detected with a synchronised gated imaging receiver. The short gate length (~ns) allowed by a micro-channel plate CCD reduces solar clutter. Detector noise is not the limiting factor because of the high MCP-CCD detectivity. Laser choice is constrained by the required laser pulse energy, laser size and robustness. The COTS solution identified is a diode-pumped, 4th harmonic converted, 1064nm laser. Nd:YAG, Nd:YLF and Nd:Alexandrite lasers have superior performance but require some development for this application. A pessimistic range model evaluates the optical powers. Comparison of the received fluorescent energy to the detector noise equivalent energy and the solar energy received provides the detection range limit. Performance of the proposed systems exceeds the detection range requirement for all samples evaluated and all varying conditions explored. The lowest range is for black paint with the COTS laser system and is 2860m; the best ranges exceed 5km.

This paper will report experiments, analysis and simulations of slant path imaging using 1.5 μm gated imaging. The measurements were taking place at a former airfield along a 2 km path. The sensor was elevated by a lift in steps from 2-12.5 meters. Targets were resolution charts. The turbulence was measured along the path with a scintillometer. Turbulence information was also obtained at various path positions including the elevated cage using anemometers. The camera was collecting both passive and active images in the SWIR region. In the passive mode (using solar illumination) the noise due to speckles are eliminated and the influence by scintillation limited. In the active mode on the other hand these noise sources are present to a varying degree depending on stabilized frame averaging and on the sensor elevation. A trend is that the image quality is improved for elevated sensor positions. Two light sources in the camera FOV (head lights from a car) gave independent turbulence level estimates. The paper will present evaluated images for both passive and active modes obtained at different elevations and the result will be compared with theory including image simulation.

Potential asymmetric threats at short range in complex environments need to be identified quickly during coastal operations. Laser range profiling is a technology that has the potential to shorten the OODA loop (Orient, Observe, Detect, Act) by performing automatic characterisation of targets at large distance. The advantages of non-cooperative target recognition with range profiles are: (a) a relatively short time on target is required, (b) the detection range is longer than in the case of passive observation technologies such as IRST, and (c) characterisation of range profiles is possible at any aspect angle. However, the shape of a range profile depends strongly on aspect angle. This means that a large data set is necessary of all expected targets with reference profiles on a very dense aspect angle grid. Analysis of laser range profiles can be done by comparing the measured profile with a database of laser range profiles obtained from 3D models of possible targets. An alternative is the use of a profile database from one or several measurement campaigns. A prerequisite for this is the availability of enough measured profiles of the appropriate targets, for many aspect angles. Comparison of measured laser range profiles with a reference database can be performed using, e.g., formal statistical correlation techniques or histogram dissimilarity techniques. In this work, a field trial has been conducted to validate the concept of identification by using a laser range profiling system with a high bandwidth receiver and short laser pulses. The field trial aimed at characterization of sea-surface targets in a coastal/harbour environment. The targets ranged from pleasure boats like sailing boats, jet skis, and speed boats to professional vessels like barges, cabin boats, and military vessels, all ranging from 3 to 30 meters in length. We focus on (a) the use of a reference database generated via 3D target models, and (b) the use of a reference database of measured laser range profiles. A variety of histogram dissimilarity measures was examined in order to enable fast and reliable classification algorithms.

Repetitive surveying of inshore waters is becoming more and more essential to evaluate reservoir sedimentation, river degradation, water flow and water level dynamics, structure and zone variations of rivers and riparian areas. This can only be achieved in an effective way by employing hydrographic airborne laser scanning. A new laser scanner for acquisition of high-resolution hydrographic data dedicated for surveying inland waters and shallow coastal zones is introduced. Measurement results obtained with the compact airborne laser scanning system employing a narrow laser beam at 532 nm, operating at a net measurement rate of 110 kHz are presented. Advantages and limitations of this new approach are discussed and potential fields of applications are assessed.

The compressive sensing (CS) theory has drawn great interest in signal processing community in recent years and led to new image acquisition techniques in many different fields. This research attempts to develop a CS based underwater laser serial imaging system. A Digital Mirror Device (DMD) based system configuration is proposed. The constraints due to scattering medium are studied. A multi-scale measurement matrix design, the "model-assisted" image reconstruction concept and a volume backscattering reduction technique are proposed to mitigate such constraints. These concepts are also applicable to CS based imager in other scattering environment such as fog, rain or clouds. Simulation results using a modified imaging model developed by HBOI and Metron and experimental results using a simple optical bench setup are presented. Finally the proposed technique is compared with traditional laser line scan (LLS) design and other structured illumination based imager.

We present experimental results of a high-speed 3-D laser scanner developed for the European Space Agency within an activity dealing with a high precision relative attitude control sensor for formation flying. By employing pulsed-time-offlight measurement, we demonstrated sub-mm accuracy and precision as well as unprecedented resolution of single-shot measurements to natural targets at distances up to 150 m. The instrument is based on RIEGL's commercial terrestrial laser scanners with a scan range of 100° x 360° and a net measurement rate of 125 kHz. The system's performance is demonstrated with different test setups and potential fields of application are assessed.

As a result of recent achievements in the field of laser radars, new options are available for their operation as system components. In addition to complementing and cross-checking one another, system components can generate new synergetic values. In this article, we address various roles and functions that laser radar may perform in a complete system context. Special attention is paid to range-gated imaging ladars operating in conjunction with infrared 2D sensors providing target recognition/identification at long distances and under adverse conditions of natural illumination. The multi- or hyper-spectral features of passive IR or visible sensors may be complemented by multispectral, broadband, tunable or switchable 3D imaging ladar in order to exploit the differences in target reflectance and absorption. This option opens another possibility for multi-spectral, mid-IR ladar to differentiate targets of various types, or to enhance the visualization potential and to facilitate the scene description with small targets like mines or mine-like objects. The recently discovered specificity of Raman scattering in the perturbed sea water makes the long-standing efforts in submarine wake detection more viable. Furthermore, the combination of microwave radar and laser radar, when amplified with new achievements in the fourth generation dual-mode imaging sensors, creates the possibility of single payload configurations suitable for small platforms. Emphasis is also made of the efficiency of Doppler velocimetry for precise vehicle navigation, such as for advance cruise missile control or autonomous landing. Finally, recent advances in coherent micro-ladars for optical coherence tomography now permit the reconstruction of time resolved 3D (i.e., 4D) dynamics of blood flow in heart vessels.

We developed a LIDAR system with a sensor head as small as 22 cc, in spite of the inclusion of a scanning mechanism. This LIDAR system not only has a small body, but is also highly sensitive. Our LIDAR system is based on time-of-flight measurements, and it incorporates an optical fiber. The main feature of our system is the utilization of optical amplifiers for both the transmitter and the receiver, and the optical amplifiers enabled us to exceed the detection limit of thermal noise. In conventional LIDAR systems the detection limit is determined by thermal noise, because the avalanche photo-diodes (APD) and trans-impedance amplifiers (TIA) that they use detect the received signals directly. In the case of our LIDAR system, received signal is amplified by an optical fiber amplifier in front of the photo diode and the TIA. Therefore, our LIDAR system can boost the signal level before the weak incoming signal is depleted by thermal noise. There are conditions under which the noise figure for the combination of an optical fiber amplifier and a photo diode is superior to the noise figure for an avalanche photo diode. We optimized the gain of the optical fiber amplifier and TIA in our LIDAR system such that it is capable of detecting a single photon. As a result, the detection limit of our LIDAR system is determined by shot noise. This small and highly sensitive measurement technology shows great potential for use in LIDAR with an optical preamplifier.

Modern small-footprint LIDAR systems have the ability to resolve structural details at sub-meter sizes, which make them ideal for collecting information to use in line-of-sight analysis. Many existing techniques used to map line-of-sight apply simple surface triangulation to the LIDAR point cloud, but are not well suited to scenes with significant 3D structure and overlapping objects. Newer voxel-based techniques have the ability to describe scene structure accurately, but typically suffer from a lack of information if all scene surfaces are not exhaustively sampled by the LIDAR. LIDAR instrument position is typically discarded after producing the point cloud, but we show how it can be used to identify areas in voxel maps where insufficient data are available. Using this knowledge of under-sampled areas we demonstrate construction of an improved line-of-sight map with metrics that indicate where and why errors in the line-of-sight are likely to occur. During the summer of 2010 an airborne experiment over the RIT campus collected both LIDAR and high resolution visible imagery. The LIDAR point cloud was sampled at several returns per square meter, and the accompanying visible imagery is used to provide context and truth information for LIDAR derived products. A realworld voxel line-of-sight map created from this LIDAR collection is presented along with an analysis of the associated derived errors.

Modern LADAR sensors have the potential to utilize a number of sensing modalities that provide a rich array of information in addition to traditional 3D geometry. Imaging polarization, multi-spectral reflectance/absorption and vibration spectral signature characteristics can all be sensed, potentially in a single LADAR sensor. This paper will examine how these rich sensing capabilities enhance the utility of LADAR signature exploitation. This research utilizes a strong understanding of underlying physical phenomena, enabling the development of data exploitation capabilities that are not brittle to small variations from assumed targets and environmental conditions, and minimizing the need for experimentally obtained training data. Physics-based signal processing research has demonstrated a promising ability to extract useful and actionable intelligence from the various sensing modalities of modern LADAR systems. A summary of the intelligence provided by the LADAR sensing modalities is presented as well as a demonstration of how the individual modes and combinations of LADAR sensing modes can be leveraged to add unique and valuable information to intelligence gathering missions. Particular utility is demonstrated for detection of adversary presence in cluttered, obstructed, hidden or underground environments. Furthermore, research has shown 3D geometry, polarization, multi-spectral and vibrometry LADAR sensing modalities can provide valuable intelligence for identifying and/or classifying the adversary and analyzing threat.

Stationary lidar (Light Detection and Ranging) systems are often used to collect 3-D data (point clouds) that can be used for terrain modelling. The lidar gathers scans which are then merged together to map a terrain. Typically this is done using a variant of the well-known Iterated Closest Point (ICP) algorithm when position and pose of the lidar scanner is not accurately known. One difficulty with the ICP algorithms is that they can give poor results when points that are not common to both scans (outliers) are matched together. With the advent of MEMS (microelectromechanical systems)-based GPS/IMU systems, it is possible to gather coarse position and pose information at a low cost. This information is not accurate enough to merge point clouds directly, but can be used to assist the ICP algorithm during the merging process. This paper presents a method called Sphere Outlier Removal (SOR), which accurately identifies outliers and inliers, a necessary prerequisite to using the ICP algorithm. SOR incorporates the information from a low cost GPS/IMU to perform this identification. Examples are presented which illustrate the improvement in the accuracy of merged point clouds when the SOR algorithm is used.

Terrain classification, or bare earth extraction, is an important component to LADAR data analysis. The terrain classification approach presented in this effort utilizes an adaptive lower envelope follower (ALEF) with an adaptive gradient operation for accommodations of local topography and roughness. In order to create a more robust capability, the ALEF was modified to become a strictly data driven process that facilitates a quick production of the data product without the subjective component associated with user inputs. This automated technique was tested on existing LADAR surveys over Wyoming's Powder River Basin and the John Starr Memorial Forest in Mississippi, both locations with dynamic topographic features. The results indicate a useful approach in terms of operational time and accuracy of the final bare earth recovery with the advantage of being fully data driven.

There is a growing need for rapid and accurate damage and debris assessment following natural disasters, terrorist attacks, and other crisis situations. This research enhances existing algorithms for LiDAR point classification (ground/non-ground), feature classification (buildings, vegetation, roads, etc.), and seeks to develop new algorithms for building damage and debris detection and quantification-work evaluated using LiDAR data of Port-au-Prince, Haiti, collected by RIT just days after the January 12, 2010 earthquake. Normalized height, height variation, intensity, and multiple return information are among the parameters being used to develop rules for building extraction and vegetation removal. Various approaches are being explored to perform damage assessment, with a focus on the slope and texture of roof planes. Initial results show a general over-segmentation in a 457x449 m region-of-interest (ROI)-the building detection algorithm autonomously identified 206 buildings, while only 98 buildings actually exist in the ROI. Further, four buildings went completely undetected. The accuracy of the damage detection algorithm was assessed only in regions where the building detection algorithm results overlapped actual building locations. The overall damage detection accuracy was 73.40%, but with a low Kappa accuracy of k = 0.275. The algorithms will be implemented in a common programming language where the processing will be optimized for large data sets. The goal is for the operational tool to be implemented in the field, using available equipment in a close to real-time environment.

Large LiDAR (Light Detection And Ranging) data sets are used to create depth mapping of objects and geographic areas. The suitability of image compression methods for these large LiDAR data sets was explored, analyzed and optimized. Our research interprets LiDAR data as intensity based "depth images", and uses k-means clustering, reindexing and JPEG2000 to compress the data. The first step in our method applies the k-means clustering algorithm to an intensity image creating a small index table, an index map and residual image. Next we use methods from previous research to re-index the index map to optimize compression when using JPEG2000. And lastly we compress both the reindexed map and residual image using JPEG2000, exploring the use of both lossless and lossy compression. Experimental results show that in general we can compress data to 23% of the original size losslessly and even further allowing for small amounts of loss.

Mobile LIDAR scanning typically provides captured 3D data in the form of 3D 'Point Clouds'. Combined with colour imagery these data produce coloured point clouds or, if further processed, polygon-based 3D models. The use of point clouds is simple and rapid, but visualisation can appear ghostly and diffuse. Textured 3D models provide high fidelity visualisation, but their creation is time consuming, difficult to automate and can modify key terrain details. This paper describes techniques for the visualisation of fused multispectral 3D data that approach the visual fidelity of polygon-based models with the rapid turnaround and detail of 3D point clouds. The general approaches to data capture and data fusion are identified as well as the central underlying mathematical transforms, data management and graphics processing techniques used to support rapid, interactive visualisation of very large multispectral 3D datasets. Performance data with respect to real-world 3D mapping as well as illustrations of visualisation outputs are included.

Several quantitative data quality metrics for three dimensional (3D) laser radar systems are presented, namely: X-Y contrast transfer function, Z noise, Z resolution, X-Y edge & line spread functions, 3D point spread function and data voids. These metrics are calculated from both raw and/or processed point cloud data, providing different information regarding the performance of 3D imaging laser radar systems and the perceptual quality attributes of 3D datasets. The discussion is presented within the context of 3D imaging laser radar systems employing arrays of Geiger-mode Avalanche Photodiode (GmAPD) detectors, but the metrics may generally be applied to linear mode systems as well. An example for the role of these metrics in comparison of noise removal algorithms is also provided.

A multiwavelength, multistatic optical scattering instrument is being developed to characterize spherical aerosols. This instrument uses 405 nm (blue), 532 nm (green) and 655 nm (red) diode lasers and two CCD imagers to measure the angular distribution of light scattered from aerosols. The incident light is polarized parallel or perpendicular to the scattering plane; the scattered intensity is measured at backscatter angles ranging from 120° to 170° by CCD imagers. The phase function for each polarization is used to form the polarization ratio, which is used to characterize the aerosols. This method has proven to be a reliable way to characterize spherical aerosols by matching the measured polarization ratio with the polarization ratio calculated by the Mie scattering equations. This method is used to determine the number density, size distribution, and index of refraction of the aerosols. The sensitivity of the polarization ratio to particle concentration is explored using a narrow distribution of one micron polystyrene beads in a chamber. The aerosol concentration is found via an inversion technique that is based on Mie calculations. This study provides the basis for transitioning this instrument to measure multiple particle size ranges and concentrations for common aerosols in an outdoor environment.

NASA Langley Research Center is working on a continuous wave (CW) laser based remote sensing scheme for the detection of CO₂and O₂ from space based platforms suitable for ACTIVE SENSING OF CO₂ EMISSIONS OVER NIGHTS, DAYS, AND SEASONS (ASCENDS) mission. ASCENDS is a future space-based mission to determine the global distribution of sources and sinks of atmospheric carbon dioxide (CO₂). A unique, multi-frequency, intensity modulated CW (IMCW) laser absorption spectrometer (LAS) operating at 1.57 micron for CO₂ sensing has been developed. Effective aerosol and cloud discrimination techniques are being investigated in order to determine concentration values with accuracies less than 0.3%. In this paper, we discuss the demonstration of a PN code based technique for cloud and aerosol discrimination applications. The possibility of using maximum length (ML)-sequences for range and absorption measurements is investigated. A simple model for accomplishing this objective is formulated, Proof-of-concept experiments carried out using SONAR based LIDAR simulator that was built using simple audio hardware provided promising results for extension into optical wavelengths.

In addition to visible and near-IR emission, recent investigations have shown that electromagnetic pulses (EMP) in the microwave and RF regions of the spectrum are generated during femtosecond laser-matter interactions if the laser source is sufficiently intense to ablate and ionize an illuminated solid target material. Although the mechanisms for the laserinduced EMP pulse are not fully characterized, it is reported that this phenomenon arises from two mechanisms associated with terawatt to petawatt level laser interactions with matter: (1) ionization via propagation in air, and (2) plasma generation associated with the laser-excited solid material. Over the past year, our group has examined the microwave emission profiles from a variety of femtosecond laser ablated materials, including metals, semiconductors, and dielectrics. We have directed our measurements towards the characterization of microwave emission from ablated surfaces in air using laser peak powers in excess of 10¹² Watts (energy/pulse ~50 mJ, pulse width ~30 fs, laser diameter at target ~200 microns). We have characterized the temporal profile of the microwave emission and determined the emission from all samples is omni-directional. We have also observed a difference in the minimum fluence required to generate emission from conducting and insulating materials although the peak amplitudes from these materials were quite similar at the upper laser energy levels of our system (~50 mJ).

Autonomous aerial refueling (AAR) is an important capability for an unmanned aerial vehicle (UAV) to increase its flying range and endurance without increasing its size. This paper presents a novel tracking method that utilizes both 2D intensity and 3D point-cloud data acquired with a 3D Flash LIDAR sensor to establish relative position and orientation between the receiver vehicle and drogue during an aerial refueling process. Unlike classic, vision-based sensors, a 3D Flash LIDAR sensor can provide 3D point-cloud data in real time without motion blur, in the day or night, and is capable of imaging through fog and clouds. The proposed method segments out the drogue through 2D analysis and estimates the center of the drogue from 3D point-cloud data for flight trajectory determination. A level-set front propagation routine is first employed to identify the target of interest and establish its silhouette information. Sufficient domain knowledge, such as the size of the drogue and the expected operable distance, is integrated into our approach to quickly eliminate unlikely target candidates. A statistical analysis along with a random sample consensus (RANSAC) is performed on the target to reduce noise and estimate the center of the drogue after all 3D points on the drogue are identified. The estimated center and drogue silhouette serve as the seed points to efficiently locate the target in the next frame.

We report on the development of a fiber-optic pulsed coherent lidar transceiver for wind-velocity and aircraft wake-vortex hazard detection. The all-fiber 1.5μm transmitter provides up to 560 μJ energy at 25 kHz with 800 ns pulse width (pump limited). Performance simulations indicate wake-vortex hazard signature detection up to ~2.5km range with a receiver sensitivity of ~2 fW (SNR=6), suited for an aircraft landing scenario. Furthermore, the transceiver is implemented using high-speed FPGA based control and digital-signal-processing, enabling its use as a flexible pulse-format multi-function in-flight lidar sensor. We present the latest laboratory results and preliminary testing of this pulsed coherent lidar transceiver, along with the lidar performance simulation of wake-vortex eddy models.

Multi-aperture coherent LADAR techniques can be applied to generate high resolution images. When setting up a system with multiple sub-apertures, misalignment of the sub-apertures causes the beams entering the sub-apertures to have mismatched optical path lengths, which will degrade the image resolution. Post-processing using image sharpening techniques to correct for piston phase, as well as other aberration corrections, require computing power and time. We study whether the processing time can be shortened by providing measured piston phase information to the image sharpening algorithms. Simulations are used to demonstrate the usefulness of piston phase measurements. Simulations are presented showing the benefits of piston phase measurements for two or more sub-apertures. The speed of convergence for the sharpening algorithm both with and without the piston phase measurements are compared for multiple sub-aperture imaging.

In this paper we present analytic models of the CNR loss or efficiency due to Gaussian line-of-sight pointing errors with bias, as a function of the correlation coefficient between the transmit and back-propagated local oscillator beams of a coherent laser radar. We also present theoretical expressions for the normalized signal power variance (a.k.a., the scintillation index) including speckle noise. This theory is developed for Gaussian targets, which converges to the point and extended target solutions, under the appropriate small and large diameter target limits. Including correlation between the transmit and back propagated local oscillator (BPLO) beams allows one to predict performance as a function of target range for a monostatic ladar, since at zero range the two beam positions are fully correlated, whereas at infinite range they are fully uncorrelated. Numerical experiments were developed and the resulting measurements are shown to agree with the analytic theory. The validated simulation tool is then exercised against other targets (e.g., a disk), for which closed form solutions are elusive. Analysis of the best-fit Gaussian target to represent the efficiency of a uniform disk target is also explored.

We have developed a laser vibrometer based on a Nd:YVO₄/YVO₄/KTP monolithic single-frequency green laser operating at 532 nm with narrow linewidth of radiation (~85kHz). Two configurations of laser Doppler vibrometer have been investigate - with so-called single- and double-frequency Bragg shifts. Measurement of heterodyne signals as a mixing result of scattered and reference beams has been performed. In both configurations we have obtained signals with high S/N ratio >30 dB with Resolution Bandwidth RBW = 200 kHz for a vibrometer output power of 3 mW. In our opinion, stable single-frequency solid-state green lasers provide new opportunities for the development of miniature laser vibrometry.

The WDM fiber transmission technique was used to measure vibration parameters of four points of a vibrating object. The 4-independent laser diodes form a WDM system according to the rule 'one wavelength-one analyzed point'. Keywords: laser Doppler vibrometry, fibre vibrometry, heterodyne detection, multichannel vibrometry.

We describe our ongoing research into a laser-seismic system for detecting and identifying buried objects from airborne platforms. We discuss generation of acoustic or high-power microwave sources in the aircraft, coupling of acoustic waves to seismic waves at the ground, frequency and bandwidth for resolution and propagation of seismic waves. Several alternative methods of generating the seismic wave include use of existing earth seismic noise, drop seismic noise makers, high power pulse acoustic source, microwave sources that causes an arc to generate acoustic noise at the earth's surface. A laser scans the region in a vibrometer interferometer configuration to measure the amplitude of the oscillations in the seismic wave at spots along the surface of the ground. The detection and identification of buried objects is determined from the seismic measurements.

The Topographic Mapping Flash Lidar (TMFL) developed at Ball Aerospace combines a pushbroom format transmitter at 1064 nm with a flash focal plane receiver. The wide 20 degree field of view of the instrument enables broad swath coverage from a single laser pulse without the need for a scanning mechanism. These features make the TMFL design particularly well-suited for space flight. TMFL has been demonstrated during an airborne flight where data were gathered over a forest plot to measure tree waveforms. Topographic maps were assembled of river beds and geologic areas of high relief. The TMFL has also been used to observe multiple-scattering phenomena in clouds by illuminating a steam plume from the aircraft above. Signal was recorded off-axis from the illuminated laser line by as much as 1 degree. The TMFL study of multiple-scattering is valuable as it provides a unique way to significantly improve the calibration of measured backscatter for space lidars. Lidar backscatter was also measured from water surface and was shown to correlate with models of water surface roughness.

The performance of Geiger-mode LAser Detection and Ranging (LADAR) cameras is primarily defined by individual pixel attributes, such as dark count rate (DCR), photon detection efficiency (PDE), jitter, and crosstalk. However, for the expanding LADAR imaging applications, other factors, such as image uniformity, component tolerance, manufacturability, reliability, and operational features, have to be considered. Recently we have developed new 32×32 and 32×128 Read-Out Integrated Circuits (ROIC) for LADAR applications. With multiple filter and absorber structures, the 50-μm-pitch arrays demonstrate pixel crosstalk less than 100 ppm level, while maintaining a PDE greater than 40% at 4 V overbias. Besides the improved epitaxial and process uniformity of the APD arrays, the new ROICs implement a Non-uniform Bias (NUB) circuit providing 4-bit bias voltage tunability over a 2.5 V range to individually bias each pixel. All these features greatly increase the performance uniformity of the LADAR camera. Cameras based on these ROICs were integrated with a data acquisition system developed by Boeing DES. The 32×32 version has a range gate of up to 7 μs and can cover a range window of about 1 km with 14-bit and 0.5 ns timing resolution. The 32×128 camera can be operated at a frame rate of up to 20 kHz with 0.3 ns and 14-bit time resolution through a full CameraLink. The performance of the 32×32 LADAR camera has been demonstrated in a series of field tests on various vehicles.

The optoelectronic gain of a linear mode avalanche photo-diode (APD) results from the cascade of electron and hole impact ionizations that take place in the high-field intrinsic multiplication layer of the APD. Due to the uncertainty associated with the stochastic nature of the APD's gain, the shot noise present in the resulting photo-generated electrical signal is accentuated and degrades the detection of single photon initiated avalanche signals. Recent advances in linearmode InGaAs APD detectors have been demonstrated that have reduced excess noise, along with the high gain necessary for detecting single photons. In these devices the avalanche buildup is characterized with a temporally varying noise. At low incident photon / photo-electron levels, the stochastic nature of the impulse response function of these APDs offers the potential of increased probability that the output exceeds a threshold level resulting in a "detection" and, hence, a better receiver-operating-characteristic (ROC). In this paper we examine the ROC (P_detection vs P_FalseAlarm) statistics of these single photon APDs as a function of the quasi-deterministic mean gain and standard deviation for an rms ROIC (readout integrated circuit) noise level of 25e^-. Single photo-electron and multiple photo-electron detection statistics are also examined for predicting a ROC. Measured linear-mode APD data are also presented.

Next generation LIDAR mapping systems require multiple channels of sensitive photoreceivers that operate in the wavelength region of 1.06 to 1.55 microns, with GHz bandwidth and sensitivity less than 300 fW/√Hz. Spectrolab has been developing high sensitivity photoreceivers using InAlAs impact ionization engineering (I²E) avalanche photodiodes (APDs) structures for this application. APD structures were grown using metal organic vapor epitaxy (MOVPE) and mesa devices were fabricated using these structures. We have achieved low excess noise at high gain in these APD devices; an impact ionization parameter, k, of about 0.15 has been achieved at gains >20 using InAlAs/InGaAlAs as a multiplier layer. Electrical characterization data of these devices show dark current less than 2 nA at a gain of 20 at room temperature; and capacitance of 0.4 pF for a typical 75 micron diameter APD. Photoreceivers were built by integrating I²E APDs with a low noise GHz transimpedance amplifier (TIA). The photoreceivers showed a bandwidth of 1 GHz and a noise equivalent power (NEP) of 150 fW/rt(Hz) at room temperature.

In this paper, we discuss the possible use of a light-weight lidar system to detect and track a sniper's high-speed bullet. The analysis includes the calculation of the beam waist, the irradiance per pulse, average irradiance, the maximum time between pulses and the minimum pulse repetition frequency, all as functions of range, beam diameter and beam quality (M²). We discuss, briefly, the possible cueing of such a lidar system by an IR system. The measurement of the BRDF of a bullet is briefly described. Finally, we report on the detection range, based on SNR calculations, as a function of energy per pulse, beam diameter and M².

We have demonstrated a 243mJ, eye-safe, injection seeded, non-critically phase-matched (NCPM), singly resonant oscillator (SRO), KTA ring-cavity optical parametric oscillator (OPO). The OPO was pumped with a single mode 7ns FWHM, 30Hz, Q-switched, Nd:YAG at a wavelength of 1064.162nm. The OPO was injection-seeded utilizing a single longitudinal (SLM) distributed feedback (DFB) diode laser. As a result, the KTA OPO generated an eye-safe signal wavelength of 1535.200nm with a maximum energy of 243mJ, a conversion efficiency of 27%, a cavity mode seed range of 853MHz FWHM, and a maximum M2=30. This high energy, eye-safe OPO could potentially increase the sensitivity and range capabilities of elastic LIDAR and DIAL systems which are used for remote sensing applications.

We describe an efficient laser emission from a directly grown Er³⁺:YAG single-crystal fiber that is resonantly pumped using a continuous-wave (CW) laser diode at 1532 nm. In a longitudinal pumping, it emits 12.5 W at 1645 nm with a slope efficiency of 32%, which is the highest ever reported for a directly grown Er:YAG single-crystal fiber laser. Using an off-axis pumping scheme, CW output powers up to 7.3 W can be reached and in Q-switched operation, the laser produces 2 mJ pulses with a duration of 38 ns at the repetition rate of 1 kHz with an M² factor below 1.8. To our knowledge this is the first directly grown Er³⁺:YAG single-crystal fiber Q-switched laser. In dual-side pumping scheme a laser emission at 1617 nm is achieved with output powers up to 5.7 W representing the highest output power ever achieved by a diode-pumped Er:YAG laser at this wavelength.

We have developed and tested an optical ranging system using a Pseudo-Random Bit Stream (PRBS) modulation technique. The optical transceiver consisted of an infrared laser transmitter co-aligned with a receiver telescope. The infrared laser beam was propagated to a retro-reflector and then received by a detector coupled to the telescope. The transceiver itself was mounted on a gimbal that could actively track moving targets through a camera that was bore sighted with the optical detector. The detected optical signal was processed in real time to produce a range measurement with sub mm accuracy. This system was tested in the field using both stationary and moving targets up to 5 km away. Ranging measurements to an aircraft were compared with results obtained by differential GPS (Global Positioning System) techniques.

In this project, we propose to develop a prototype system that can automatically reconstruct 3D scenes of the interior of a building, cave or other structure using ground-based LIDAR scanning technology. We develop a user-friendly real-time visualization software package that will allow the users to interactively visualize, navigate and walk through the room from different view angles, zoom in and out, etc.

We demonstrate new results using our Spectral LADAR prototype, which highlight the benefits of this sensor for Unmanned Ground Vehicle (UGV) navigation applications. This sensor is an augmentation of conventional LADAR and uses a polychromatic source to obtain range-resolved 3D spectral point clouds. These point cloud images can be used to identify objects based on combined spatial and spectral features in three dimensions and at long standoff range. The Spectral LADAR transmits nanosecond supercontinuum pulses generated in a photonic crystal fiber. Backscatter from distant targets is dispersed into 25 spectral bands, where each spectral band is independently range resolved with multiple return pulse recognition. Our new results show that Spectral LADAR can spectrally differentiate hazardous terrain (mud) from favorable driving surfaces (dry ground). This is a critical capability, since in UGV contexts mud is potentially hazardous, requires modified vehicle dynamics, and is difficult to identify based on 3D spatial signatures. Additionally, we demonstrate the benefits of range resolved spectral imaging, where highly cluttered 3D images of scenes (e.g. containing camouflage, foliage) are spectrally unmixed by range separation and segmented accordingly. Spectral LADAR can achieve this unambiguously and without the need for stereo correspondence, sub-pixel detection algorithms, or multi-sensor registration and data fusion.

The Army Research Laboratory (ARL) is researching a short-range ladar imager for navigation, obstacle/collision avoidance, and target detection/identification on small unmanned ground vehicles (UGV).To date, commercial UGV ladars have been flawed by one or more factors including low pixelization, insufficient range or range resolution, image artifacts, no daylight operation, large size, high power consumption, and high cost. ARL built a breadboard ladar based on a newly developed but commercially available micro-electro-mechanical system (MEMS) mirror coupled to a lowcost pulsed Erbium fiber laser transmitter that largely addresses these problems. Last year we integrated the ladar and associated control software on an iRobot PackBot and distributed the ladar imagery data via the PackBot's computer network. The un-tethered PackBot was driven through an indoor obstacle course while displaying the ladar data realtime on a remote laptop computer over a wireless link. We later conducted additional driving experiments in cluttered outdoor environments. This year ARL partnered with General Dynamics Robotics Systems to start construction of a brass board ladar design. This paper will discuss refinements and rebuild of the various subsystems including the transmitter and receiver module, the data acquisition and data processing board, and software that will lead to a more compact, lower cost, and better performing ladar. The current ladar breadboard has a 5-6 Hz frame rate, an image size of 256 (h) × 128 (v) pixels, a 60° × 30° field of regard, 20 m range, eyesafe operation, and 40 cm range resolution (with provisions for super-resolution or accuracy).

The purpose of this research is to develop a new 3D LIDAR sensor, named KIDAR-B25, for measuring 3D image information with high range accuracy, high speed and compact size. To measure a distance to the target object, we developed a range measurement unit, which is implemented by the direct Time-Of-Flight (TOF) method using TDC chip, a pulsed laser transmitter as an illumination source (pulse width: 10 ns, wavelength: 905 nm, repetition rate: 30kHz, peak power: 20W), and an Si APD receiver, which has high sensitivity and wide bandwidth. Also, we devised a horizontal and vertical scanning mechanism, climbing in a spiral and coupled with the laser optical path. Besides, control electronics such as the motor controller, the signal processing unit, the power distributor and so on, are developed and integrated in a compact assembly. The key point of the 3D LIDAR design proposed in this paper is to use the compact scanning mechanism, which is coupled with optical module horizontally and vertically. This KIDAR-B25 has the same beam propagation axis for emitting pulse laser and receiving reflected one with no optical interference each other. The scanning performance of the KIDAR-B25 has proven with the stable operation up to 20Hz (vertical), 40Hz (horizontal) and the time is about 1.7s to reach the maximum speed. The range of vertical plane can be available up to ±10 degree FOV (Field Of View) with a 0.25 degree angular resolution. The whole horizontal plane (360 degree) can be also available with 0.125 degree angular resolution. Since the KIDAR-B25 sensor has been planned and developed to be used in mobile robots for navigation, we conducted an outdoor test for evaluating its performance. The experimental results show that the captured 3D imaging data can be usefully applicable to the navigation of the robot for detecting and avoiding the moving objects with real time.

A method to determine correct focus in direct detection laser radar system using Geiger-mode avalanche photodiode focal plane array (GmAPD-FPA) is proposed. It is implemented by laser pulses with controlled beam diameter and energy on a distant target. And the time-of-flight (TOF) of laser pulses are obtained for each pixel in GmAPD-FPA. With multiple laser pulses, time correlated single photon counting (TCSPC) is carried out to obtain target detection probability. Using target detection probabilities of each pixel, the photon distribution on GmAPD-FPA is acquired. The condition to determine correct focus is the minimum photon distribution in GmAPD-FPA. In theory part, the range of laser pulse energy is decided. The experiments are carried out with commercial 1x8 pixel GmAPD-FPA. The experimental results show that the focus position is founded using this method and a spatial resolution of a laser radar system is improved where the 1x8 pixel GmAPD-FPA is located in focus position.

LIDAR system for real-time standoff detection of bio-agents is presented and preliminary experimental results are discussed. The detection approach is based on two independent physical phenomena: (1) laser induced fluorescence (LIF), (2) depolarization resulting from elastic scattering on non-spherical particles. The device includes three laser sources, two receiving telescopes, depolarization component and spectral signature analyzing spectrograph. It was designed to provide the stand-off detection capability at ranges from 200 m up to several kilometers. The system as a whole forms a mobile platform for vehicle or building installation. Additionally, it's combined with a scanning mechanics and advanced software, which enable to conduct the semi-automatic monitoring of a specified space sector. For fluorescence excitation, 3-rd (355 nm) and 4-th (266 nm) harmonics of Nd:YAG pulsed lasers are used. They emit short (~6 ns) pulses with the repetition rate of 20 Hz. Collecting optics for fluorescence echo detection and spectral content analysis includes 25 mm diameter f/4 Newton telescope, Czerny Turner spectrograph and 32-channel PMT. Depending on the grating applied, the spectral resolution from 20 nm up to 3 nm per channel can be achieved. The system is also equipped with an eye-safe (1.5 μm) Nd:YAG OPO laser for elastic backscattering/depolarization detection. The optical echo signal is collected by Cassegrain telescope with aperture diameter of 12.5 mm. Depolarization detection component based on polarizing beam-splitter serves as the stand-off particle-shape analyzer, which is very valuable in case of non-spherical bio-aerosols sensing.

Full-waveform LIDAR is a technology which enables the analysis of the 3-D structure and arrangement of objects. An in-depth understanding of the factors that affect the shape of the full-waveform signal is required in order to extract as much information as possible from the signal. A simple model of LIDAR propagation has been created which simulates the interaction of LIDAR energy with objects in a scene. A 2-dimensional model tree allows controlled manipulation of the geometric arrangement of branches and leaves with varying spectral properties. Results suggest complex interactions of the LIDAR energy with the tree canopy, including the occurrence of multiple bounces for energy reaching the ground under the canopy. Idealized sensor instrument response functions incorporated in the simulation illustrate a large impact on waveform shape. A waveform recording laser rangefinder has been built which will allow validation or model results; preliminary collection results are presented here.