Proceedings Volume 6550

Laser Radar Technology and Applications XII

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Proceedings Volume 6550

Laser Radar Technology and Applications XII

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Volume Details

Date Published: 3 May 2007
Contents: 9 Sessions, 27 Papers, 0 Presentations
Conference: Defense and Security Symposium 2007
Volume Number: 6550

Table of Contents

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Table of Contents

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  • Front Matter: Volume 6550
  • Coherent Systems
  • 3D Imaging Systems and Applications I
  • 3D Imaging Systems and Applications II
  • Test and Evaluation
  • Imaging through Obscurants I
  • Imaging through Obscurants II
  • Security Applications
  • Components
Front Matter: Volume 6550
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Front Matter: Volume 6550
This PDF file contains the front matter associated with SPIE Proceedings Volume 6550, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.
Coherent Systems
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High-resolution 3D coherent laser radar imaging
Joseph Buck, Andrew Malm, Andrew Zakel, et al.
The Super-resolution Sensor System (S3) program is an ambitious effort to exploit the maximum information a laser-based sensor can obtain. At Lockheed Martin Coherent Technologies (LMCT), we are developing methods of incorporating multi-function operation (3D imaging, vibrometry, polarimetry, aperture synthesis, etc.) into a single device. The waveforms will be matched to the requirements of both hardware (e.g., optical amplifiers, modulators) and the targets being imaged. The first successful demonstrations of this program have produced high-resolution, three-dimensional images at intermediate stand-off ranges. In addition, heavy camouflage penetration has been successfully demonstrated. The resolution of a ladar sensor scales with the bandwidth as dR = c/(2B), with a corresponding scaling of the range precision. Therefore, the ability to achieve large bandwidths is crucial to developing a high-resolution sensor. While there are many methods of achieving the benefit of large bandwidths while using lower bandwidth electronics (e.g., an FMCW implementation), the S3 system produces and detects the full waveform bandwidth, enabling a large set of adaptive waveforms for applications requiring large range search intervals (RSI) and short duration waveforms. This paper highlights the three-dimensional imaging and camo penetration.
Coherent ladar imaging of the SEASAT satellite retro-reflector array using linear-FM chirp waveforms and pulse-compression
Coherent ladar imaging of satellite retro-reflector arrays is analyzed to determine some of the potential capabilities of coherent ladar systems for long range imaging. The satellites are at mega-meters of slant range and are basically angularly unresolved assuming a nominal one meter telescope used at a laser wavelength of 1.064 μm corresponding to a 281,625 GHz center-frequency. A coherent ladar may have a selectable waveform ranging from single nanosecond pulses through tone-pulses, but the imaging waveform considered here is the linear-FM chirp pulse-compression ladar waveform, which consists of a series of frequency chirps over a long period of time. The linear-FM chirp return is pulse compressed digitally using several possible approaches. Image reconstruction follows basic ISAR algorithms in forming a "range-resolved Doppler and intensity" (RRDI) image. A retro-reflector ring on the SEASAT satellite is used to illustrate the ladar's capability, although we spin the satellite faster than the true rotation rate to demonstrate waveform resolution. Several other useful algorithms as (multi-chirp) range-time-intensity (RTI matrix) range-bin summation and segmented-spectrum frequency-bin summation are also discussed. A covariance matrix calculation is applied to the RTI matrix and also to the segmented-spectrum matrix for the extraction of additional target information.
3D Imaging Systems and Applications I
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Chirped amplitude modulation ladar for range and Doppler measurements and 3-D imaging
Barry Stann, Brian C. Redman, William Lawler, et al.
Shipboard infrared search and track (IRST) systems can detect sea-skimming anti-ship missiles at long ranges, but cannot distinguish missiles from slowly moving false targets and clutter. In a joint Army-Navy program, the Army Research Laboratory (ARL) is developing a ladar to provide unambiguous range and velocity measurements of targets detected by the distributed aperture system (DAS) IRST system being developed by the Naval Research Laboratory (NRL) sponsored by the Office of Naval Research (ONR). By using the ladar's range and velocity data, false alarms and clutter objects will be distinguished from incoming missiles. Because the ladar uses an array receiver, it can also provide three-dimensional (3-D) imagery of potential threats at closer ranges in support of the force protection/situational awareness mission. The ladar development is being accomplished in two phases. In Phase I, ARL designed, built, and reported on an initial breadboard ladar for proof-of-principle static platform field tests. In Phase II, ARL was tasked to design, and test an advanced breadboard ladar that corrected various shortcomings in the transmitter optics and receiver electronics and improved the signal processing and display code. The advanced breadboard will include a high power laser source utilizing a long pulse erbium amplifier built under contract. Because award of the contract for the erbium amplifier was delayed, final assembly of the advanced ladar is delayed. In the course of this year's work we built a "research receiver" to facilitate design revisions, and when combined with a low-power laser, enabled us to demonstrate the viability of the components and subsystems comprising the advanced ladar.
Dual-band spacecraft sensor suite for lunar and small-body landing
B. G. Boone, K. Strohbehn, B. E. Kluga, et al.
NASA is planning missions to small planetary bodies in which low-risk high-accuracy soft-landing must be accomplished independent of ground control. Accurate estimates of range, descent rate, attitude, and translational drift rate are needed for precision landings (< 1 m CEP) in low gravity. Operational ranges for the landing phase are expected to vary from a kilometer down to one meter. Poorly characterized landing sites may require real-time obstacle avoidance. Although passive sensors are being considered, active sensors enable the spacecraft to exploit more optimal measurement techniques in which surface illumination is controlled by design rather than accommodated by default. This paper addresses the development and validation of a robust combination of sensors, which reduce risks while minimizing spacecraft mass and power. This paper describes the design, test, and evaluation of two sensors: a miniature pulsed Nd:YAG lidar and a Ka-band CW Doppler radar. These sensors are co-bore sighted on a two-axis gimbal, along with an inertial measurement unit and a data acquisition PC on a mobile test-bed. Test results will be presented and discussed for conditions that emulate appropriate landing operations. Fixed test structures with corner reflector targets are used to validate this approach and calibrate sensor sensitivity to different geometries and kinematics.
Characterization of 3-D imaging lidar for hazard avoidance and autonomous landing on the Moon
Future robotic and crewed lunar missions will require safe and precision soft-landing at scientifically interesting sites near hazardous terrain features such as craters and rocks or near pre-deployed assets. Presently, NASA is studying the ability of various 3-dimensional imaging sensors particularly lidar/ladar techniques in meeting its lunar landing needs. For this reason, a Sensor Test Range facility has been developed at NASA Langley Research Center for calibration and characterization of potential 3-D imaging sensors. This paper describes the Sensor Test Range facility and its application in characterizing a 3-D imaging ladar. The results of the ladar measurement are reported and compared with simulated image frames generated by a ladar model that was also developed as part of this effort. In addition to allowing for characterization and evaluation of different ladar systems, the ladar measurements at the Sensor Test Range will support further advancement of ladar systems and development of more efficient and accurate image reconstruction algorithms.
Correlation between LIDAR and radar reflux intensity and the accuracy of the associated elevation information
G. Heidelmeyer, B. Eilmus, U. Klingauf
Due to upcoming new data driven technologies in the aviation the impact of digital terrain data is growing conspicuously. Especially for ground near operations reliable terrain information is necessarily demanded. Based on modern earth observation technologies a new generation of elevation data is obtainable. However, it shall be analysed how far data derived from remote sensing techniques like INSAR (Interferometric Synthetic Aperture Radar) or LIDAR (Light Detection And Ranging) can be applied to aviation purposes. Typically, terrain data were represented in relation to the bare earth to obtain a "Digital Terrain Model" (DTM). For aviation purposes a "Digital Surface Model" (DSM) representing the real surface of the earth including all cover like vegetation and buildings is recommended (see Fig. 4). But due to the characteristics of active remote sensors the derived model always describes an in between of the two elevation representations. To satisfy these special requirements of the aviation the Institute of Flight Systems and Automatic Control (FSR) at the Technische Universität Darmstadt is dealing with the determination of the influencing factors which affect the quality of the terrain models being appropriate to be used as a DSM. Intention of this study is to identify how far the reflux intensity of LIDAR and radar beams affects the quality of the associated elevation model. By knowing the cause and the impact of the deviations a "Safety Buffer" will be determined in order to increase the integrity of the terrain data to allow the applicability for dedicated applications (Fig. 3).
Distributed aperture active imaging
Joseph C. Marron, Richard L. Kendrick
With a distributed aperture imaging system, one creates a large imaging aperture by combining the light from a series of distributed telescopes. In doing this, one can construct a fine-resolution imaging system with reduced volume. In this paper we present work on distributed aperture, active imaging systems that use coherent detection and digital image formation. In such a system, the image formation process incorporates digital correction of optical and atmospheric phase errors. Here we discuss the principles underlying this method and present results from laboratory experiments and field experiments performed over a 0.5 km outdoor test range.
3D Imaging Systems and Applications II
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Aerial vehicle navigation over unknown terrain environments using inertial measurements and dual airborne laser scanners or flash LADAR
Ananth K. Vadlamani, Maarten Uijt de Haag
A precise navigation system for uninhabited or inhabited aerial vehicles is discussed in this paper. The navigational capability of an aerial vehicle must be robust and not easily influenced by external factors. Nowadays, many navigation systems rely somehow on the Global Positioning System (GPS), wherein the GPS signals may be rendered unusable due to unintentional interference caused by atmospheric effects, interference from communication equipment, as well as intentional jamming. The navigation method discussed in this paper integrates measurements from an Inertial Measurement Unit (IMU) with measurements from either two airborne laser scanners (ALS) or an airborne Flash LADAR (AFL) to provide autonomous navigational capability and a reliable alternative to GPS. The proposed system has applications in unknown or partially known terrain environments or it may also be used for autonomous landing systems in Lunar or Martian environments. Two approaches are described in this paper, one approach uses Dual Airborne Laser Scanners (DALS) (one pointing forward, the other pointing aft) and the other approach uses an AFL. Advantages and disadvantages of both approaches are discussed. The proposed navigation system uses strapdown IMU measurements to estimate the aerial vehicle position and attitude and to geo-reference the laser sensor data. It then uses the maps created from both the fore and aftpointing scanning LADARS or the consecutive Flash LADAR range-images to estimate systematic IMU errors such as position and velocity drifts. The proposed navigation algorithm is evaluated using flight test data from Ohio University's DC3 aircraft and synthesized ALS and AFL measurements. Initial results are observed to achieve meter level accuracies in the system's position drift performance.
Use of 3D laser radar for navigation of unmanned aerial and ground vehicles in urban and indoor environments
This paper discusses the integration of Inertial measurements with measurements from a three-dimensional (3D) imaging sensor for position and attitude determination of unmanned aerial vehicles (UAV) and autonomous ground vehicles (AGV) in urban or indoor environments. To enable operation of UAVs and AGVs at any time in any environment a Precision Navigation, Attitude, and Time (PNAT) capability is required that is robust and not solely dependent on the Global Positioning System (GPS). In urban and indoor environments a GPS position capability may not only be unavailable due to shadowing, significant signal attenuation or multipath, but also due to intentional denial or deception. Although deep integration of GPS and Inertial Measurement Unit (IMU) data may prove to be a viable solution an alternative method is being discussed in this paper. The alternative solution is based on 3D imaging sensor technologies such as Flash Ladar (Laser Radar). Flash Ladar technology consists of a modulated laser emitter coupled with a focal plane array detector and the required optics. Like a conventional camera this sensor creates an "image" of the environment, but producing a 2D image where each pixel has associated intensity vales the flash Ladar generates an image where each pixel has an associated range and intensity value. Integration of flash Ladar with the attitude from the IMU allows creation of a 3-D scene. Current low-cost Flash Ladar technology is capable of greater than 100 x 100 pixel resolution with 5 mm depth resolution at a 30 Hz frame rate. The proposed algorithm first converts the 3D imaging sensor measurements to a point cloud of the 3D, next, significant environmental features such as planar features (walls), line features or point features (corners) are extracted and associated from one 3D imaging sensor frame to the next. Finally, characteristics of these features such as the normal or direction vectors are used to compute the platform position and attitude changes. These "delta" position and attitudes are then used calibrate the IMU. Note, that the IMU is not only required to form the point cloud of the environment expressed in the navigation frame, but also to perform association of the features from one flash Ladar frame to the next. This paper will discuss the performance of the proposed 3D imaging sensor feature extraction, position change estimator and attitude change estimator using both simulator data and data collected from a moving platform in an indoor environment. The former consists of data from a simulated IMU and flash Ladar installed on an aerial vehicle for various trajectories through an urban environment. The latter consists of measurements from a CSEM Swissranger 3D imaging sensor and a MicroStrain low-cost IMU. Data was collected on a manually operated aerial vehicle inside the Ohio University School of Electrical Engineering and Computer Science building.
Test and Evaluation
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ASTM E57 3D imaging systems committee: an update on the standards development effort
Alan M. Lytle, Gerry Cheok, Kamel Saidi
In June 2006, a new ASTM committee (E57) was established to develop standards for 3D imaging systems. This committee is the result of a 4-year effort at the National Institute of Standards and Technology to develop performance evaluation and characterization methods for such systems. The initial focus for the committee will be on standards for 3D imaging systems typically used for applications including, but not limited to, construction and maintenance, surveying, mapping and terrain characterization, manufacturing (e.g., aerospace, shipbuilding), transportation, mining, mobility, historic preservation, and forensics. This paper reports the status of current efforts of the ASTM E57 3D Imaging Systems committee.
Advanced measurements optical range (AMOR) ladar test facility
The Advanced Measurements Optical Range (AMOR) began operations in 1978 with a mission to measure ladar target signatures of ballistic missiles and to advance the understanding of object features useful for discrimination of reentry vehicles from decoy objects. Ground breaking ladar technology developments and pioneering ladar target signature studies were completed in the early years of AMOR operations. More recently, AMOR functions primarily as a user test facility measuring ladar signatures of a diverse set of objects such as reentry vehicles and decoys, missile bodies, and satellite materials as well as serving as a ladar sensor test-bed to recreate realistic missile defense engagement scenarios to exercise and test missile seeker technologies. This paper gives a status report on current AMOR capabilities including the optical system, target handling system, laser systems, and data measurement types. Plans for future facility enhancements to provide improved service to ladar data users in the modeling and simulation field and to ladar system developers with requirements for advanced test requirements are also reported.
A validation procedure for a LADAR system radiometric simulation model
The USU LadarSIM software package is a ladar system engineering tool that has recently been enhanced to include the modeling of the radiometry of Ladar beam footprints. This paper will discuss our validation of the radiometric model and present a practical approach to future validation work. In order to validate complicated and interrelated factors affecting radiometry, a systematic approach had to be developed. Data for known parameters were first gathered then unknown parameters of the system were determined from simulation test scenarios. This was done in a way to isolate as many unknown variables as possible, then build on the previously obtained results. First, the appropriate voltage threshold levels of the discrimination electronics were set by analyzing the number of false alarms seen in actual data sets. With this threshold set, the system noise was then adjusted to achieve the appropriate number of dropouts. Once a suitable noise level was found, the range errors of the simulated and actual data sets were compared and studied. Predicted errors in range measurements were analyzed using two methods: first by examining the range error of a surface with known reflectivity and second by examining the range errors for specific detectors with known responsivities. This provided insight into the discrimination method and receiver electronics used in the actual system.
MRDF and BRDF measurements of low-scatter materials
Bidirectional reflectivity distribution function (BRDF) measurement results are reported for the monostatic case and for small bistatic angles for several low-scatter diffuse materials illuminated at the 1.064 &mgr;m and 532 nm wavelengths. Materials such as ESLI Vel-Black, Edmund Scientific flocked paper, and 2% Spectralon were measured. All materials were measured using both co-polarized and cross-polarized transmit-receive configurations. The MRDF/BRDF scatterometer at the Advanced Measurements Optical Range (AMOR) at Redstone Arsenal in Huntsville, Alabama was used for these measurements and is described here; this beamsplitter-based system can make BRDF measurements with incidence angles from 0 to 80° and with in-plane and out-of-plane bistatic angles from + 3.5° through -3.5°, including the monostatic point.
Dead-time effects on geiger-mode APD performance
Phillip Gatt, Steven Johnson, Terry Nichols
Geiger mode avalanche photodiodes (GAPDs) are capable of detecting single photon events. However, once triggered, GAPDs must be reset or rearmed to enable the detection of another event. Thus, these devices are non-linear and their performance depends on the reset-time a.k.a. dead-time. In this paper, the performance of GAPD based ladar receivers is investigated and a theory for the signal photon detection efficiency (SPDE) is developed as a function of the dead-time; signal, noise and clutter flux; and the GAPD's photon detection efficiency or PDE. This SPDE theory is valid for arbitrary (short to long) dead-times. With a zero dead-time, GAPDs behave linearly and the SPDE theory converges to the PDE. For long dead-times, compared to the acquisition gate time, the theory converges to previously published works of Fouche and Williams. This SPDE theory is then applied to develop a theory for the detector signal-to-noise ratio (SNR). The performance improvement when multiple micro-pixels are grouped to form a macro pixel is also discussed.
Imaging through Obscurants I
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High-resolution foliage penetration with gimbaled lidar
Michael W. Roth, Jason C. Hunnell, Kevin E. Murphy, et al.
Foliage penetration is a major application of airborne lidar systems. Typical ground resolutions achieved for floodplain-mapping applications are of the order of meters. Much higher ground resolution can be achieved by integrating multiple looks from several look-angles. This paper describes a new system that can achieve very high ground sampling densities in forested environments at significant altitudes (6 kft) using a modified commercial lidar and a custom gimbal system. Absolute calibration of the gimbal system demonstrated pointing knowledge comparable to the usual aircraft-fixed lidar performance (0.1-0.2 mrad). Bare-earth processing of the resultant data enables interactive virtual deforestation relative to a high-resolution ground.
Jigsaw phase III: a miniaturized airborne 3-D imaging laser radar with photon-counting sensitivity for foliage penetration
Mohan Vaidyanathan, Steven Blask, Thomas Higgins, et al.
Jigsaw three-dimensional (3D) imaging laser radar is a compact, light-weight system for imaging highly obscured targets through dense foliage semi-autonomously from an unmanned aircraft. The Jigsaw system uses a gimbaled sensor operating in a spot light mode to laser illuminate a cued target, and autonomously capture and produce the 3D image of hidden targets under trees at high 3D voxel resolution. With our MIT Lincoln Laboratory team members, the sensor system has been integrated into a geo-referenced 12-inch gimbal, and used in airborne data collections from a UH-1 manned helicopter, which served as a surrogate platform for the purpose of data collection and system validation. In this paper, we discuss the results from the ground integration and testing of the system, and the results from UH-1 flight data collections. We also discuss the performance results of the system obtained using ladar calibration targets.
Imaging through Obscurants II
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A texture-based technique for DEM generation from LIDAR data
Dimitrios Charalampidis, Keith Alphonso
Obtaining high resolution Digital Elevation Models (DEMs) is a critical task for analysis and visualization in several remote sensing applications. LIDAR technology provides an effective way for obtaining high-resolution topographic information. This paper presents a texture-based novel automatic algorithm for DEM generation from LIDAR data. The proposed technique uses multifractal-based textural features for object identification, combined with a maximum slope filter. Although this work is concentrated on DEM generation, certain aspects of the algorithm make it suitable for classification of LIDAR data into other types of data. Some experimental results are presented to illustrate the effectiveness of the proposed algorithm.
Performance of laser penetration through forest vegetation
One of the major advantages with laser sensors compared to passive optronic sensors, is the capability to penetrate sparse vegetation. Therefore, the most limiting performance issue is the portion of laser "shots" being absorbed by the foliage. This issue is the main focus in this paper and an analysis of the effect of forest vegetation of Nordic type is presented. The conclusions are based on laser scanner measurement as well as photos. While the analysis covers several elevation angles, the evaluation focuses on ground-to-ground measurements.
Identification of littoral targets with a laser range profiler
Naval operations in the littoral have to deal with threats at short range in cluttered environments with both neutral and hostile targets. On board naval vessels there is a need for fast identification, which is possible with a laser range profiler. Additionally, in a coast-surveillance scenario a laser range profiler can be used for identification of small sea-surface targets approaching the coast. An eye-safe 1.5 μm laser range profiler has been used to validate these claims. Experimental results show that range profiles of sea-surface targets can be obtained at ranges of several km's. Sea-surface clutter is shown to be negligible. Simulation shows that sea-surface targets can be distinguished from their range profiles. The influence on the identification performance of range resolution and a-priori knowledge of the aspect angle is presented. Classification has been tested on simulated range profiles of a number of small boats. With a range resolution of 0.3 meter (comparable to our experimental set-up), these small boats could be identified.
Utilization of full-waveform data in airborne laser scanning applications
Andreas Ullrich, Markus Hollaus, Christian Briese, et al.
Direct detection laser radar systems with echo signal digitization and subsequent full waveform analysis provide additional information on the target's properties compared to conventional discrete echo systems. We focus on the advantages of utilizing the additional information especially in the course of airborne laser scanning, improving for example the mandatory process for classifying the measurement data for generating high-quality digital terrain models. We present field data to demonstrate the superiority of full-waveform data over conventional laser data.
Security Applications
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Container integrity verification using laser triangulation
Axel Busboom, Vítor Sequeira
We present a system for verifying the integrity of storage containers using a laser triangulation scanner, with applications in nuclear security. Any intrusion into the container shell and subsequent reconstruction of the surface inevitably leaves slight changes to the three-dimensional surface structure which the proposed system can detect. The setup consists of a laser line scanner, mounted on a rotation stage. We propose an auto-calibration procedure for this system which − from several scans of a planar calibration target acquired from different viewpoints − automatically determines the position and orientation of the rotation axis with respect to the scanner coordinate frame. We further present an algorithm for the automatic registration of two 3D scans of a cylindrical surface, not requiring any user interaction such as the identification of corresponding point pairs. We show that the algorithm accurately aligns two scans of the same object, acquired from different viewpoints. The accuracy of the overall system is dominated by the measurement uncertainty of the 3D scanner; residual errors resulting from the calibration and registration are subordinate. The system can reliably detect changes in the surface shape resulting from tampering.
Multi-static networked 3D ladar for surveillance and access control
A theoretical design and simulation of a 3D ladar system concept for surveillance, intrusion detection, and access control is described. It is a non-conventional system architecture that consists of: i) multi-static configuration with an arbitrarily scalable number of transmitters (Tx's) and receivers (Rx's) that form an optical wireless code-division-multiple-access (CDMA) network, and ii) flexible system architecture with modular plug-and-play components that can be deployed for any facility with arbitrary topology. Affordability is a driving consideration; and a key feature for low cost is an asymmetric use of many inexpensive Rx's in conjunction with fewer Tx's, which are generally more expensive. The Rx's are spatially distributed close to the surveyed area for large coverage, and capable of receiving signals from multiple Tx's with moderate laser power. The system produces sensing information that scales as NxM, where N, M are the number of Tx's and Rx's, as opposed to linear scaling ~N in non-network system. Also, for target positioning, besides laser pointing direction and time-of-flight, the algorithm includes multiple point-of-view image fusion and triangulation for enhanced accuracy, which is not applicable to non-networked monostatic ladars. Simulation and scaled model experiments on some aspects of this concept are discussed.
Detection of small sea-surface targets with a search lidar
Naval operations in the littoral have to deal with the threat of small sea-surface targets. These targets have a low radar cross-section and low velocity, which makes them hard to detect by radar in the presence of sea clutter. Typical threats include periscopes, jet skies, FIAC's, and speedboats. Search lidars on board naval vessels can provide detection capability for small sea-surface targets. Lidar measurements at the coast have shown a very good signal-to-clutter ratio with respect to buoys located up to 10 km from the shore were the lidar system was situated. The lidar clutter is much smaller than the radar clutter due to the smoothness of the sea surface for optical wavelengths, thus almost all laser light is scattered away from the receiver. These results show that due to the low clutter a search lidar is feasible that can detect small sea-surface targets. The concept of a search lidar is presented and its performance is derived from system models. By using a high rep-rate laser and a variable beam divergence the search time can be limited. The design of a search lidar based on a commercially available high power and high rep-rate laser is shown.
Components
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Closed loop optimization of opto-mechanical structure via mechanical and optical analysis software
This paper will discuss how mechanical and optical analysis software can be used together to optimize an opto-mechanical structure subjected to vibrational loading. Mechanical analysis software output is post processed into Zernike polynomial coefficients and rigid body motions for analysis with optical modeling software. Structural modifications can then be implemented to improve optical performance. A Cassegrain telescope, which can be utilized for laser radar applications, will be used to demonstrate this optimization. Two FEA solution methods are compared. Based on the deformation results of the FEA, Zernike polynomials and rigid body motions are generated and applied to the optical surfaces in CODE V®. The effect of these deformations on wavefront can then be computed and compared to a required performance.
Progress in laser risk reduction for 1 micron lasers at GSFC
In recent years, lasers have proven themselves to be invaluable to a variety of remote sensing applications. LIDAR techniques have been used to measure atmospheric aerosols and a variety of trace species, profile winds, and develop high resolution topographical maps. Often it would be of great advantage to make these measurements from an orbiting satellite. Unfortunately, the space environment is a challenging one for the high power lasers that would enable many LIDAR missions. Optical mounts must maintain precision alignment during and after launch. Outgassing materials in the vacuum of space lead to contamination of laser optics. Electronic components and optical materials must survive the space environment, including a vacuum atmosphere, thermal cycling, and radiation exposure. Laser designs must be lightweight, compact, and energy efficient. Many LIDAR applications require frequency conversion systems that have never been designed or tested for use in space. For the last six years the National Aeronautical and Space Administration (NASA) has undertaken a program specifically directed at addressing the durability and long term reliability issues that face space-borne lasers. The effort is shared between NASA Goddard Space Flight Center in Greenbelt, Maryland, and NASA Langley Research Center in Hampton, Virginia. This paper is an overview of the issues facing space-borne lasers and the efforts that Goddard has been pursuing to address them.
Improving lifetime of quasi-CW laser diode arrays for pumping 2-micron solid state lasers
Farzin Amzajerdian, Byron L. Meadows, Nathaniel R. Baker, et al.
Operating high power laser diode arrays in long pulse regime of about 1 msec, which is required for pumping 2-micron thulium and holmium-based lasers, greatly limits their useful lifetime. This paper describes performance of laser diode arrays operating in long pulse mode and presents experimental data on the active region temperature and pulse-to-pulse thermal cycling that are the primary cause of their premature failure and rapid degradation. This paper will then offer a viable approach for determining the optimum design and operational parameters leading to the maximum attainable lifetime.