Proceedings Volume 3380

Laser Radar Technology and Applications III

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Proceedings Volume 3380

Laser Radar Technology and Applications III

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Volume Details

Date Published: 8 September 1998
Contents: 7 Sessions, 38 Papers, 0 Presentations
Conference: Aerospace/Defense Sensing and Controls 1998
Volume Number: 3380

Table of Contents

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Table of Contents

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  • Atmospheric Sensing
  • Transmitter Laser Technology
  • Receiver and Detector Technology
  • Modeling and Simulation
  • Laser Ranging and Signature Measurement
  • Imaging Sensors
  • Atmospheric Sensing
  • Poster Session
  • Transmitter Laser Technology
  • Laser Ranging and Signature Measurement
Atmospheric Sensing
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Space Readiness Coherent Lidar Experiment (SPARCLE) Space Shuttle Mission
For over 20 years researchers have been investigating the feasibility of profiling tropospheric vector wind velocity from space with a pulsed Doppler lidar. Efforts have included theoretical development, system and mission studies, technology development, and ground-based and airborne measurements. Now NASA plans to take the next logical step towards enabling operational global tropospheric wind profiles by demonstrating horizontal wind measurements from the Space Shuttle in early 2001 using a coherent Doppler wind lidar system.
Multiparametric lidar system spanning from UV to mid IR
Paolo F. Ambrico, Aldo Amodeo, Salvatore Amoruso, et al.
A new multiparametric lidar system spanning from UV to mid IR is presently under testing. The system is based on two Optical Parametric Amplifier (OPA) lasers pumped by a Nd:YAG laser operating at a maximum pulse repetition rate of 100 Hz. OPA lasers represent a new design for coherent radiation sources continuously tunable in the UV-IR range. The large range of tunability of OPA lasers allows to perform Differential Absorption Lidar measurements in a spectral region where most of atmospheric pollutants display absorption lines. The system has been designed to deliver simultaneously in the atmosphere the Nd:YAG fundamental and its harmonics (II and III) as well as the four output beams of the two OPA lasers. The return signals, collected by means of two Newtonian telescopes, can be used to retrieve information on: atmospheric aerosols, water vapor and pollutants concentration, atmospheric temperature, density and transmissivity profiles. In this paper a detailed description of the system is reported. Moreover, some results obtained by a multiparametric system (based on a Nd:YAG pumped dye laser) are reported to show the capabilities of a multiwavelength lidar system.
Heterodyne measurements of stratospheric ozone using a single sideband tunable CO2 laser
Kambiz Shahnazi, Lahmer Lynds
Heterodyne detection of ozone in the stratosphere has been demonstrated using a tunable single sideband CO2 laser as the local oscillator and solar radiation acquired at ground level. Two unblended strong O3 vibrational- rotational transitions at 1047.209 and 1047.225 cm-1 which were offset at 10.66 and 11.12 GHz away from the CO2 carrier 9P20 were observed. High resolution measurements at 5 MHz (0.00017 cm-1) with a signal to noise ratio of 100:1 were obtained. The measured FWHM linewidths for these lines are about approximately equals 65 MHz. Retrieved data indicated magnitude of absorption is consistent with the anticipated integrated O3 column density from the stratospheric region.
Coherent lidar crosswind sensing
Philip Gatt, J. Alex L. Thomson, Stephen M. Hannon
Range-resolved crosswind measurements are required for improved ballistics accuracy in a variety of planetary boundary layer applications. In these environments, the effects wind turbulence can cause large errors in estimates derived using conventional Velocity Azimuth Display (VAD) lidar techniques. This paper presents the results from two recent measurement campaigns employing the VAD algorithm and Monte Carlo performance predictions of a novel velocity- pattern tracking concept for precision range-resolved crosswind sensing in the presence of wind turbulence.
Transmitter Laser Technology
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Laser radar development
This paper discusses the trends in laser radar development. Applications include reconnaissance and targeting from airborne and spaceborne platforms. A multifunction airborne sensor system, which includes a laser radar function with many modes, is defined. A multidiscriminant space borne laser radar is also described and its feasibility is assessed. A number proposed and existing Air Force programs to develop laser radar technology are described.
Diode-pumped Er:glass lasers Q-switched by BBO E/O Q-switch and FTIR methods
Ruikun Wu, John D. Myers, Scott J. Hamlin
Erbium doped phosphate glass lasers, utilizing both BBO Pockel's cell and FTIR Q-switching methods have achieved operation up to 3 KHz.
Mid-infrared multiwavelength source for lidar applications
Allen R. Geiger, Egor V. Degtiarev, William H. Farr, et al.
Differential absorption lidars (DIAL) in the mid-infrared (2 - 5 micrometers ) are used to monitor various chemical species. Two wavelengths are required to perform the differential absorption measurement: an `on' line and an `off' line. Previously, the measurement has been made by sequentially tuning between the two lines. However, this can produce errors in the measured differential absorption, especially when a DIAL is used in a `look down' reflector mode from a high speed aircraft, because of variations in the Earth's reflectivity between laser pulses. To avoid this problem and to construct a high speed DIAL system, LaSen, Inc. has developed an intra-cavity `stacked' optical parametric oscillator/laser (OPOL), which is capable of producing simultaneous tunable outputs in the 2 - 5 micrometers region. This laser system utilizes a compact diode pumping scheme and an overlapped laser/OPO resonator design that produces multiple wavelength outputs and minimizes the number of optical components and optical path length. The decreased size of the OPOL system and increased ruggedness makes it ideal for man-portable and airborne operation.
Development of high-pulse energy Ho:Tm:YLF coherent transmitters
NASA Langley has developed a diode-pumped, room temperature Ho:Tm:YLF coherent pulsed transmitter for SPARCLE, a NASA approved space shuttle mission. The acronym stands for SPAce Readiness Coherent Lidar Experiment and is expected to fly in 2001. SPARCLE mission objective is to carry out first ever global wind measurement from space. The laser transmitter for SPARCLE is a Ho:Tm:YLF power oscillator operating at eye-safe wavelength of 2.05 micrometers . The Q- switched output energy is 125 mJ at six Hz, and it has a near-transform limited beam with a pulse width of 170 ns. The high power and high beam quality of this laser makes it well suited as a coherent wind lidar transmitter on a space platform. When the output of this power oscillator is amplified by using four diode-pumped Ho:Tm:YLF amplifiers, an output energy of 600 mJ at 10 Hz has been achieved. This is the highest energy ever produced at 10 Hz, and is at least an order of magnitude greater than previously achieved for 2-micrometers diode-pumped laser at room temperature.
Frequency-stabilized diode-pumped Tm,Ho:YLF local oscillator with + 4 GHz of tuning range
Hamid Hemmati, Carlos Esproles, Robert T. Menzies
A tunable, single-frequency, frequency-stabilized, diode- pumped Tm,Ho:YLF laser is described. The laser, which demonstrates the function of a local-oscillator for coherent Doppler lidar in space, has continuous frequency tunability of more than 8 GHz. Active frequency stabilization is achieved by feedback electronics which allow for controlled tuning capability. Output power of more than 20 mW in single-transverse and -longitudinal mode operation with a short term frequency jitter of less than 100 kHz/ms is obtained.
Semiconductor and fiber laser development at Air Force Research Laboratory Directed Energy Directorate
Michael R. Gregg, David J. Bossert, David J. Gallant, et al.
This paper will review Air Force Research Laboratory Directed Energy Directorate development programs which provide high-efficiency electric semiconductor diode lasers and diode pumped fiber lasers for a host of applications including free space communications, laser radar, illuminators, trackers and designators.
Novel optical Doppler frequency detector based on moving space charge field effects in semiconductors and its application to laser raders
Chen Chia Wang, Sudhir B. Trivedi, Ronald G. Rosemeier
We review the principles of a new kind of optical Doppler frequency detectors and their applications to laser radars. These novel optical frequency sensors are based on the recently investigated moving space charge field effects found in photoconductive semiconductors. The photocurrent generated by the moving space charge field photodetectors is linearly proportional to the Doppler frequency shift suffered by the probing signal beam relative to the local reference laser beam and constitutes the unique directional discrimination capability in optical frequency detection not easily found in other forms of Doppler frequency detection schemes. Application of these novel Doppler frequency detectors to laser radars lead to significantly compact, economical, and power efficient systems. Simple feasibility demonstration of the proposed concept is also presented.
Ladar using broadband optical source
Roland K. Appel, William N. Dawber, John Lockwood
A simultaneously broadband laser has been developed for laser radar applications. Simultaneous broadband operation is important in enabling rapid (single pulse) data measurement, avoiding atmospheric scintillation or turbulence effects that can dog a more conventional laser which is sequentially tuned to a series of probe wavelengths. The laser is based on an optical parametric oscillator operating in a non-collinear critical phase matching geometry, thereby enabling broadband operation. (beta) -Barium Borate is pumped by a frequency tripled NdYAG laser to achieve lasing from 500 - 1220 nm. The laser is further able to simultaneously lase at an arbitrary series of narrow wavelengths chosen to correspond to the absorption lines of a trace gas. The laser has been demonstrated with an output pulse energy exceeding 40 mJ with an instantaneous full bandwidth greater than 150 nm in the visible. The paper describes the current state of the laser development program. Laboratory and test trial results are presented.
Receiver and Detector Technology
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Laser radar with atomic vapor ultranarrowband image detectors (UBID)
Oleg I. Matveev, Benjamin W. Smith, James D. Winefordner
The basic characteristics, figures of merit and potential applications of laser radar with atomic vapor ultra- narrowband imaging detectors (UBID) are discussed. One of the most important figures of merit of a narrowband imaging spectrometer used in a laser radar is the product of throughput and spectral resolution. The atomic vapor UBID, compared with all known spectral imaging instruments, can potentially have a throughput-resolution product up to a million times greater. It is theoretically shown that despite hyperfine structure, one can have smooth characteristics well-suited for an ultranarrowband resonance ionization image detector (RIID) by choosing an appropriate ionization scheme for Cs atoms using the 894.3 nm line. Recent experiments with a vacuum cell mercury atomic vapor RIID are described.
Laser radar focal plane array for three-dimensional imaging: update
Richard D. Richmond, Roger Stettner, Howard Bailey
Previous efforts to develop 3D laser radar (ladar) imagers have required multiple laser pulses and complex stable scanning and timing systems in order to generate images. This paper describes an approach that will enable a complete 3D ladar image (angle-angle-range) to be captured with a single pulse. Using a unique processor chip that is bump bonded directly behind the detector array, the sensor provides separate independent range finder circuitry for each pixel. The time-of-flight for each pixel is recorded on the chip and the values are then read out serially. This approach allows the range resolution to be determined by the laser pulse width and electronics bandwidth and to be independent of image framing rates. This paper will discuss the status of the imager that is being assembled as well as preliminary results from laboratory demonstrations. The specifications of the demonstration unit are for a 32 X 32 pixel imager with a resolution of .3X.3X.3 meters (1X1X1 foot). The system is expected to operate at approximately video framing rates (30 frames per second) and the resulting image will be displayed in a false color picture on the processor monitor.
Ultrafast InGaAs pin detector for eye-safe lidar
Eyesafe LIDAR systems require detectors that operate in the 1.55 micron band with high bandwidth and large area. This paper describes the three design methods used in developing such detectors. First, a thick dual-depletion width pin structure is optimized for low capacitance and transit time. This enables the detector itself to have the best intrinsic speed. Second a extra-low input impedance preamplifier is designed. This preamplifier improves the performance of the already fast pin by lowering the electrical time-constants of the readout. Third, a novel partitioned detector layout is developed. This technique allows the connection of a large number of small, high-speed segments in parallel to form a single large detector. When used in combination, these design methods can produce a new class of detectors with diameters greater than 1 mm and bandwidths greater than 4 GHz.
Demodulation schemes for vibrometers and associated effects on target classification
Brendan Ruck, Harvey Lewis, Andrew M. Rogoyski, et al.
Non co-operative target identification using laser vibrometry is typically based upon characterization of the frequency spectra obtained after demodulating the vibrometer's output signal. The characterization uses information gleaned from certain identifiable features, such as tonals, which can be extracted from the vibration spectra. The success of this classification is dependent upon the performance of the demodulation scheme adopted. This paper investigates a number of different digital demodulation strategies that can be used on down-shifted and digitized vibrometer output in which the gross Doppler term has been removed. This paper presents an assessment of the likely impact of demodulation schemes upon several critical classification cues, for example signal-to-noise ratio, frequency and bandwidth. These cues help to parameterize the vibration spectrum and may in themselves be used to classify targets. Only digital schemes are considered here, in contrast to conventional vibrometer technology which uses analogue demodulation schemes. The investigations take the form of a general review, followed by a detailed description of each demodulation method. Each method is applied to a representative modulated signal, and its performance assessed qualitatively. Of key importance in this analysis are the different time-frequency representations (TFRs) of the digitized vibrometer signal, in addition to phase- differencing methods, which are used to derive the instantaneous frequency. TFRs which have been examined are the short-time Fourier Transform, Wigner and Choi-Williams distributions.
Modeling and Simulation
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Upgrades to DELTAS NRC (Defense Laser Target Signatures Code) for the evaluation of advanced ladar technologies
Biff Lyons, Michael Timmins
DELTASNRCTM is a laser radar signature modeling and simulation code that was developed to evaluate potential LADAR systems for defense applications. DELTASNRCTM strength is in its flexibility. The user can create scenarios with realistic targets (the target model is based on constructive solid geometry) and real materials, and model coherent or direct detection LADAR systems at any wavelength (limited only to availability of material reflectance information). This paper focuses on recent improvements to the direct and coherent detection imaging capabilities of the code. These improvements were mandated by the BMDO Discriminating Interceptor Technology Program (DITP) which requires LADAR system models for the next generation of LADAR imaging systems on an interceptor platform. We introduce upgrades to the range-Doppler imaging algorithms that improve the fidelity of the laser cross section calculation and the range-Doppler image. We describe a model that introduces ambiguity in direct detection angle- angle-range images as a result of pulse duration and detector bandwidth. A direct detection receiver model has also been implemented. This model introduces optical modulation transfer functions and receiver noise to the direct detection images. The result of these improvements is an end-to-end LADAR simulation which can be used as a stand alone code or as part of a suite of sensor models capable of generating signatures which can be used for discrimination algorithm development, system analysis, etc. Demonstrations of these improvements as applied to DITP are presented, and a discussion of current applications of DELTASNRCTM in simulations such as Synthetic Scene Generation Model is included.
Numerical evaluation of the M parameter for direct detection ladar
Douglas G. Youmans, George A. Hart
In direct detection ladar systems, the received irradiance statistics and, therefore, the detected photon counting statistics are determined by two parameters: the average collected irradiance value and the M parameter. The M parameter is the number of independent speckle cells, per polarization and per independent laser mode, subtended by the receiving aperture and focused onto a detector. In the 1960's Goodman analytically determined the M parameter for simple ladar geometries such as circular, square, and Gaussian shaped targets and circular and square shaped receiving apertures. This paper examines the numerical evaluation of this M parameter for arbitrarily shaped target source regions, per pixel or per pixel-range-bin, and arbitrarily shaped receiving apertures using the 2D discrete Fourier transform. This evaluation method is capable of treating the cases of high reflectivity target source regions, such as a cylinder's or cone's glint-line, and Gaussian spatial mode illumination which effectively reduce the source area. The analyses apply when round-trip atmospheric scintillation effects are negligible.
Laser Ranging and Signature Measurement
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Ranging accuracy analysis for the NRL@SOR satellite laser ranging capability
Mark A. Davis, G. Charmaine Gilbreath
The Naval Research Laboratory satellite laser ranging system, integrated on the 3.5 meter telescope at the USAF Starfire Optical Range, collected measurements from March 1995 through February 1997. During this period, several engineering upgrades were performed which affected key components of the ranging measurements. Most notably, the use of an amplifier boosted signal returns and increased yield at low elevations, the use of which impacted the accuracy of the measurements. An analysis of the system accuracy is presented for the campaigns and configurations. A `round robin' technique of using a calibration satellite to independently confirm residual signatures in the GPS-35 and GPS-36 ephemerides is demonstrated.
Error analysis for laser-based metric calibration of the Naval Space Surveillance System
Paul W. Schumacher Jr., G. Charmaine Gilbreath, Edward D. Lydick, et al.
The Naval Space Surveillance System is a network of continuous-wave VHF interferometer stations designed to detect Earth satellites. Angular metric data from the system are used in real time to update the catalog of known space objects maintained by the Air Force and Naval components of United States Space Command. For many years, the system has operated with a near real-time calibration of the detector electronics but without a rigorous tie to an external reference frame. One way to establish such a tie is by comparing system measurements with data derived by Satellite Laser Ranging. In principle, public-domain laser ranging data on geodetic satellites can always be used to generate a few high-precision reference orbits whose ephemerides can be compared with surveillance measurements. In the right circumstances, special laser tracking data on any suitable satellite can be taken simultaneously with surveillance measurements and compared directly. Both approaches offer benefit to space surveillance operations, and both have been demonstrated in previous work. This analysis initiates the analytical investigation of how precisely we can resolve errors in the surveillance measurements, using laser ranging-derived data. Equations are presented which relate surveillance measurement uncertainties to reference data uncertainties in explicit terms. Simple geometric measurement models are considered, rather than detailed physical measurement models, in order to provide fundamental understanding of how errors transform in the two types of calibration considered. The resulting formulae are suitable for deriving calibration requirements and simplified error budgets, either analytically or by numerical simulation.
Sequential orbit determination for GPS-35 and GPS-36 using SLR data from NRL@SOR
Richard S. Hujsak, G. Charmaine Gilbreath
A coordinated Satellite Laser Ranging campaign was conducted in late 1996 to collect tracking data for two Global Positioning System satellites, designated as GPS-35 and GPS- 36. These satellites were equipped with laser retroreflectors to provide an independent means of tracking and verifying GPS ephemeris accuracy. Historically, GPS SLR data has been too sparse to determine an accurate SLR- derived reference orbit. Previous investigations have been limited to reporting SLR range residuals which were computed by comparing to GPS ephemerides. The present investigation benefits from two innovations. The first is the addition of the Naval Research Laboratory laser ranging system at the USAF Starfire Optical Range, which provided enough additional tracking data to make precision orbit determination possible. The second is the use of a sequential filter-smoother to process the SLR data instead of the batch least squares orbit determination methods employed in earlier investigations. A filter-smoother combines the best features of short arc and long arc estimation methods, optimizing the solution for each track of data. In this application the 3D solution is most accurate over each laser ranging site. The filter-smoother generates a continuous solution with variable accuracy, and provides a covariance which characterizes that accuracy. In this study we have verified the 3D accuracy of GPS ephemerides to within 10 cm, 30 cm, 12 cm (radial, intrack, crosstrack) over selected SLR sites using an SLR-only solution. These results were achieved with very little tracking data. Additional results are provided which indicate sensitivities to tracking geometry, average monthly tracking rates, and to track duration.
Determination of TiPS libration using laser radar
William James Barnds, Shannon L. Coffey, Mark A. Davis
This paper describes the use of satellite laser ranging data for determining the orbital and librational motion of the Tether Physics and Survivability (TiPS) experiment. We provide a description of new analytical tools and methodologies developed for determining the dynamics of the system. The results gleaned from a year's worth of laser tracking are presented to provide a history of the librational and rotational motion of the TiPS system. Finally, the case for using SLR for libration determination on future tether experiments is presented.
Applications of the HI-CLASS (high-performance CO2 laser radar surveillance sensor) laser system for active imaging of space objects
Debora E. Mosley, Charles L. Matson, Stanley R. Czyzak
The HI-CLASS is a high power, wideband, coherent laser radar (ladar) for long range detection, tracking, and imaging located at the Maui Space Surveillance Site. HI-CLASS will be used to provide high precision metrics as well as information for images of space objects and remote sensing with the same system. The four phases of the HI-CLASS hardware development program were completed in Fall 1997. During this development contract, hardware and software were developed for two different modes of operation; a ladar mode for active imaging of satellites, and a lidar model for remote sensing atmospheric measurements. Throughout the contract, data were collected which provided a demonstration of the system capabilities which validated technology and designs required for fielding operational systems. The HI- CLASS follow-on demonstration program is currently being performed under an Air Force contract. The follow-on demonstrations will provide the groundwork to an upgrade program currently under consideration by the Air Force. HI- CLASS provides high accuracy tracking in position and velocity simultaneously, and by ultimately providing size, shape and orientation information, it will help assess adversary capabilities. HI-CLASS has the potential to address operational areas of need for increased capability for information about space objects. The follow-on contract effort and the HI-CLASS upgrade effort will provide a demonstration of these potential applications of the HI- CLASS system.
Coherent burst laser ranging
Eric A. Wachter, Walter G. Fisher, Michael L. Keltos
A novel signal encoding and decoding method for laser ranging is described. The coherent burst method achieves high precision ranging based on simultaneous analysis of time-of-flight and phase shift of an amplitude modulation pattern that is electronically coherent with a master oscillator. High frequency modulation provides high absolute precision, while measured temporal delay from transmission to reception eliminates uncertainty from aliasing. Demodulation of the coherent burst signal is achieved using quadrature analysis. Electronic coherence between the coherent burst modulation pattern and a master oscillator is used to generate analytic signals representing the real and imaginary components of the demodulated return signal. These components are used to determine magnitude and phase of a vector representing the signal from the target. The phase of this vector provides an estimate of phase shift between the return signal and the master oscillator, while the leading edge of the magnitude envelope is used to obtain an estimate of time-of-flight.
Agile multiple-pulse coherent lidar for range and micro-Doppler measurement
Stephen M. Hannon, J. Alex L. Thomson, Sammy W. Henderson, et al.
A novel high time-bandwidth product waveform lidar has been developed. The lidar operates at the eyesafe 2 micrometers wavelength and produces a sequence of two or more cavity- dumped pulselets with a controllable intra-pulse spacing. The number of and spacing for the individual pulselets is adjusted to match the target and atmospheric characteristics. This waveform agility enables the sensor to operate at very long stand-off ranges. Performance predictions and results from recent field demonstrations are described.
Imaging Sensors
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Three-beam scanning laser radar microprofilometer
Vasyl V. Molebny, Gary W. Kamerman, Eugene M. Smirnov, et al.
In many scientific and technologic applications, for example, in ophthalmology, microelectronics, etc, the problem exists of profile investigation with nanometer accuracy. Double-frequency phase-difference interferometric technique is known, that uses phase difference measurement between two beams propagation to the investigated surface and back at two different carrier frequencies. These measurements give profile's derivative along the line of scanning, that can be reconstructed into the profile using mathematical operation of integration. To get high accuracy, integration error must be excluded or compensated. It can be easily done, if special specimen plate is used with reference plane. Live objects, like human cornea, have no reference planes or points. We report here on the technique using measurement of two partial derivatives, thus enabling correct reconstruction of a 3D surface. Three laser beams are configured in acousto-optical system of modulators and scanners, in which partial derivatives are measured in each point for orthogonal X and Y directions. For this purpose, two modulators are positioned in series, producing alternatively neighboring beam pairs oriented along X or Y axis and having the same frequency difference for both directions. For image format 512 X 512, corresponding to investigated area 7 X 7 mm, with chosen geometry and frequency difference (f1 - f2) equals 1 MHz, time of measurement in each point is about 1 microsecond, resulting in total time less than 0.3 sec. per frame. The instrument is sensitive to profile variations less than 4 nm.
Polarization diversity active imaging
We present the concept of a Polarization Diversity Active Imager operating at (lambda) equals 810 nm. Each pixel of the image is encoded by the polarization degree Pd (0% < Pd < 100%) given by its Mueller Matrix. The measurement of the Mueller matrices is obtained using the Dual Rotation Retarder Technique. A theoretical analysis and an experimental validation of this technique are presented. The device is operating in a monostatic configuration, using a semiconductor laser ((lambda) equals 810 nm) to illuminate the target and a telescope to create the image on a CCD matrix. The experiment is controlled by a computer that drives the rotation of the retarders, the digitalization and the encoding of the image. The measured intensity and polarization images are compared and the information contained in the polarization degree are analyzed. Dual images (intensity-polarization) of different targets are presented, showing the experimental validation of the technique. The application of this active imager to the detection and the decamouflage of target buried in the background (same albedo but different polarization degree) is proposed.
Comparison of imaging laser radars based on range gating under different weather conditions
Arno von der Fecht, Hendrik Rothe
This paper discusses the development and the experimental results of two imaging laser radar systems based on range gating. We designed an 128 X 128 pixel laser radar working at the eye-safe wavelength of 1574 nm without a scanner. The laser is a Q-switched, flashlamp pumped, Nd:YAG laser with Optical Parametric Oscillator. It achieves 60 mJ output energy at the video range of 25 Hz. As detector we use a high sensitive (68% quantum efficiency) InGaAs camera with a special designed Electro-Optical Modulator objective providing 18 ns gating time. The first laser illuminated images will be presented. The second system is working at the wavelength of 532 nm and uses a gated viewing camera including a Multi Channel Plate II generation with a maximum gain of 18000. We examined the system performance under different weather conditions especially at a range between 500 m and 1500 m. For both systems the field of view is fixed at 12 mrad, that means we illuminate a 12 X 12 m field at 1 km range. The outdoor experiments were taken over a period of 2 weeks, where we had on the one hand sun and on the other hand light and moderate rain with a rainrate up to 10 mm/h and a visibility of 490 m.
Laser radar in adverse weather
Laser radar images of an outdoor target scene were collected in adverse weather such as rain and fog during the course of one year. Included in this collection is imagery in fogs with visibilities less than 2 km and rains with rain rates of up to 60 mm/hr. The targets were calibrated panels at 510 m and 1 km. The laser radar system used was a direct- detection 1.06 micrometers system designed to operate at 2 km in clear weather. For the purposes described here, though, the maximum range gate was set to 1.5 km. The system used a correlation technique for detection and discrimination, which significantly reduced the number of false returns in fog. Using these collected images, dropout pixels and false returns were correlated with rain rate and visibility. Extinction coefficients for 1.064 micrometers laser light were also calculated as a function of rain rate and visibility in fog and rain conditions. These coefficients were found to be consistent with those measured previously at 0.55 micrometers , 0.63 micrometers and 10.6 micrometers . These coefficients can be used to predict the performance of any circular polarized 1.064 micrometers LADAR system in rain and fog conditions.
Video guidance sensor flight experiment results
Richard T. Howard, Thomas C. Bryan, Michael L. Book
An active video sensor system for determining target range and attitude was flown on STS-87. The Video Guidance Sensor (VGS), developed at NASA's Marshall Space Flight Center, demonstrated its capability in space and collected performance data. The VGS was designed to provide near-range sensor data as part of an automatic rendezvous and docking system. The sensor determines the relative positions and attitudes between the active sensor and the passive target. The VGS uses laser diodes to illuminate retro-reflectors in the target, a solid-state camera to detect the return from the target, and a frame grabber and digital signal processor to convert the video information into the relative positions and attitudes. The system is designed to operate with the target within a relative azimuth of +/- 9.5 degrees and a relative elevation of +/- 7.5 degrees. The system will acquire and track the target within the defined field-of- view between 1.5 meters and 110 meters range, and the VGS is designed to acquire at relative attitudes of +/- 10 degrees in pitch and yaw and at any roll angle. The sensor outputs the data at 5 Hz, and the target and sensor software and hardware have been designed to permit two independent sensors to operate simultaneously. This allows for redundant sensors. The data from the flight experiment includes raw video data from the VGS camera, relative position and attitude measurements from the VGS, solar angle data, and Remote Manipulator System position data to correlate with the VGS data. The experiment was quite successful and returned significant verification of the sensor's capabilities. The experience gained from the design and flight of this experiment will lead to improved video sensors in the future.
Low-cost high-resolution video-rate imaging optical radar
John T. Sackos, Robert O. Nellums, Steve M. Lebien, et al.
Sandia National Laboratories has developed a unique type of portable low-cost range imaging optical radar (laser radar or LADAR). This innovative sensor is comprised of an active floodlight scene illuminator and an image intensified CCD camera receiver. It is a solid-state device (no moving parts) that offers significant size, performance, reliability, and simplicity advantages over other types of 3D imaging sensors. This unique flash LADAR is based on low- cost, commercially available hardware, and is well suited for many government and commercial uses. This paper presents an update of Sandia's development of the Scannerless Range Imager technology and applications, and discusses the progress that has been made in evolving the sensor into a compact, low cost, high-resolution, video rate Laser Dynamic Range Imager.
Model-based target recognition in ladar imagery
Qinfen Zheng, Sandor Z. Der
A pulsed ladar based object recognition system will applications to automatic target recognition is reported. The approach used is to fit the sensed range images to the range templates extracted using laser physics based simulation of Computer Aided Design target models. A projection based pre-screener filters out more than 80 percent of candidate templates. An M of N pixel matching scheme for internal shape matching combined with a silhouette matching scheme is used for recognition. The system has been blind tested on a data set containing 276 real ladar images of military vehicles at various orientations. The system achieves above 90 percent accuracy in recognition.
Atmospheric Sensing
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Laser sensing application using an amplitude locked loop
Olivier Jerome Dussarrat, D. Fraser Clark, T. J. Moir
In this paper, the demodulation characteristics of an amplitude locked loop (ALL) integrated into a laser sensing system are presented. The laser sensing system used here is a free space laser Doppler vibrometer which could be used for detecting the frequency of vibration of an object. The sensitivity of such a device is impaired by interference arising from spurious scattering along the propagation path. Mathematical and experimental investigations concluded that this interference pattern is identical to cochannel interference encountered in conventional radio-wave frequency modulation. By incorporating an ALL with a phase locked loop in the demodulator of the optical system, a dramatic improvement over 10 dB Sinad (measurement done with no psophometer) was found over existing technology.
Poster Session
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Novel method for ocean lidar air-submarine laser communication
Recent decades blue-green laser submarine communication (LSC) system has been developed as an important inter-medium transmission method for submarine communication. But the developed LSC system has only one-way communication from an air platform to a submerged platform. In this paper, a novel method is introduced for a new possible two-way LSOctober 1, 1998C system in future. All underwater modulable hollow retro-reflector in ocean has been developed for this purpose. The new system may establish a round optical link channel and allows for two-way communication from air to submarine and back.
Automatic docking system sensor: analysis and mission performance
John Larkin Jackson, Richard T. Howard, Helen Johnson Cole, et al.
The Video Guidance Sensor was flown on STS-87 in November of 1997 and is the key element of an automatic rendezvous and docking program under development by NASA Marshall Space Flight Center. The system used laser illumination of a passive target in the field of view of an on-board camera and processed the video image to determine the relative position and attitude between the target and the sensor. Comparisons of mission results with theoretical models are discussed.
Hollow-waveguide integrated optics for 10.6-um lidar
Richard Michael Jenkins, R. W. J. Devereux, A. F. Blockley
A novel integrated optic approach to the manufacture of 10.6 micrometers coherent laser radar systems is described and demonstrated. The approach uses hollow waveguides to guide light between system components which are integrated into a common substrate. The design, manufacture and operation of a seven element laser radar subsystem which is compact, rugged and provides a mixing efficiency in excess of 80% of the theoretical maximum, is discussed. Experiments which confirm the validity of the design criteria upon which the system is based are described. The demonstration of the subsystem as a simple homodyne vibrometer is also outlined.
Transmitter Laser Technology
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Wavelength selection for long-range laser vibration sensing
Joel F. Fontanella, David E. Roberts, David R. Shoup
The possibility of using remote laser vibration measurement for target identification and other purposes continues to attract interest and research in several countries. In the past, the only available laser technology capable of providing, in a compact transmitter package, the required single-frequency laser power for long range laser vibration sensing against unenhanced targets, was CO2 laser technology. Recent developments in laser transmitter technology have opened up the possibility of using solid state lasers operating in the eyesafe region (wavelength > 1.4 micrometers ) as the transmitter in future long range laser vibration sensors. This paper discusses some of the factors which must be considered in selecting a laser transmitter source for such systems. These factors include vibration measurement sensitivity at the required operating ranges, atmospheric extinction, pointing and tracking requirements, atmospheric turbulence, and eye safety. We conclude that selection of the operating wavelength and transmitter technology must be tailored to each individual application, and should not be presumed to be a foregone conclusion.
Laser Ranging and Signature Measurement
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Airborne laser swath mapping: results from project laser
William E. Carter, Ramesh L. Shrestha
During October 1996, the University of Florida, the Florida Department of Environmental Protection, the Florida Department of Transportation and the United States Geological Survey-Center for Coastal Geology and Regional Marine Studies jointly conducted a demonstration/test project of airborne laser swath mapping. Project Laser Swath-mapping Evaluation and Resurvey, included mapping of more than three hundred kilometers of beaches, stretching from Mexico Beach, just east of Panama City, Florida, to the western tip of Perdido Key, Alabama. The observations collected along the beaches included returns from the water surface at a number of inlets and from near short portions of the Gulf. The typical flying altitude during the tests was 350 meters above the surface, with an airspeed of 75 meters per second. The laser swatch mapping system operated at 5000 pulses per second, and scanned in a saw tooth pattern with a scan angle of plus and minus 15 degrees and a scan rate of 25 Hz. More than 50 million data points were collected in about three hours of operations, spread over three days. Proprietary computer software was used by the vendor to combine aircraft orientation (roll, pitch and yaw) values from an inertial navigation unit in the laser scanning unit, the angular orientation of the scanner mirror, and the range data to compute vectors from the aircraft to the reflecting surface. These vectors were added to the location of the aircraft, determined by phase difference kinematic Global Positioning System observations to compute the coordinates of the reflecting surface at each measurement epoch, expressed in UTM Northings and Eastings and ellipsoid heights. Commercial software was then used to create a variety of products, including 3D shaded relief `snapshots,' contour maps, false colored maps, cross sections and profiles. Repeat coverage was used to estimate the short term repeatability of the measurements and comparisons with cross sections from classical surveying methods were used to estimate the accuracy of the airborne laser swath mapping results.