douglas youmans - Academia.edu (original) (raw)

Papers by douglas youmans

NASA STI/Recon Technical Report N, Nov 5, 1986

Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling pre... more Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling previously established for two waveguides to a two dimensional array. In the theoretical portion of the program, two-dimensional array mode relative oscillator strengths (E-field distributions) were derived analytically for the first time. Fourier analysis of these array-modes indicated that almost an (nxm)2 increase (as for an array which is superimposed into one waveguide)in the far-field peak irradiance distribution would be achieved. The experimental program employed 1x7 and 2x3 arrays. Severe vacuum and materials problems were encountered with the 1x7 array. The 2x3 array achieved output powers of up to 8W per channel; on installation of ZnSe coupling windows the power decreased by an order of magnitude. Lasing could be achieved with all channels. No phase-locking was observed with either the 1x7 or 2x3 array for any of twenty different resonator configuration employed, including those using focussed and unfocussed grating. Folded resonator modes were found to dominate certain resonator configurations.

NASA STI/Recon Technical Report N, Nov 5, 1986

Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling pre... more Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling previously established for two waveguides to a two dimensional array. In the theoretical portion of the program, two-dimensional array mode relative oscillator strengths (E-field distributions) were derived analytically for the first time. Fourier analysis of these array-modes indicated that almost an (nxm)2 increase (as for an array which is superimposed into one waveguide)in the far-field peak irradiance distribution would be achieved. The experimental program employed 1x7 and 2x3 arrays. Severe vacuum and materials problems were encountered with the 1x7 array. The 2x3 array achieved output powers of up to 8W per channel; on installation of ZnSe coupling windows the power decreased by an order of magnitude. Lasing could be achieved with all channels. No phase-locking was observed with either the 1x7 or 2x3 array for any of twenty different resonator configuration employed, including those using focussed and unfocussed grating. Folded resonator modes were found to dominate certain resonator configurations.

Proceedings of SPIE, May 19, 2015

Backscatter from atmospheric aerosols and molecular nitrogen and oxygen causes “clutter” noise in... more Backscatter from atmospheric aerosols and molecular nitrogen and oxygen causes “clutter” noise in direct detection ladar applications operating within the atmosphere. The backscatter clutter is more pronounced in multiple pulse, high PRF ladars where pulse-averaging is used to increase operating range. As more and more pulses are added to the wavetrain the backscatter increases. We analyze the imaging of a transmitted Gaussian laser-mode multi-pulse wave-train scatteried off of aerosols and molecules at the focal plane including angular-slew rate resulting from optical tracking, angular lead-angle, and bistatic-optics spatial separation. The defocused backscatter images, from those pulses closest to the receiver, are analyzed using a simple geometrical optics approximation. Methods for estimating the aerosol number density versus altitude and the volume backscatter coefficient of the aerosols are also discussed.

Proceedings of SPIE, Apr 17, 1995

Basing laser radar systems aboard aircraft provides capability for accurate tracking of ground, a... more Basing laser radar systems aboard aircraft provides capability for accurate tracking of ground, airborne, and ballistic missile targets from long range. The atmospheric effects of long propagation paths impact the performance of laser radar systems in two important ways -- molecular and aerosol extinction and optical turbulence. This paper provides quantitative assessment of the impact of these effects for laser radar wavelengths beyond 1.4 microns. The treatment of round-trip turbulence on direct detection systems is believed to be the first estimate of this effect. A more complete system analysis is underway and will be described in a forthcoming paper.

Proceedings of SPIE, Mar 1, 1974

Proceedings of SPIE, Sep 5, 2000

The number of photons returning from a target in a given time interval is a negative-binomially d... more The number of photons returning from a target in a given time interval is a negative-binomially distributed random variable. The resulting detected photon 'electron pulses' produced by a photomultiplier tube (PMT) photon-counting detector are also negative-binomially distributed per time bin with a reduced mean. These time distributed electron pulses are amplified and filtered by the receiver electronics, prior to digitization and signal processing. The voltage output pulse per individual photo-electron event is known as the 'impulse-response- function' of the detector and amplifier. The random summation of these voltage impulse-responses, as created by the negative-binomial photon arrival times and photo-electron creation, is the classical electronic 'shot-noise' random process. We derive the voltage probability density function of this 'negative-binomial driven shot-noise' random process following the stochastic process literature. We also show a technique to include PMT variations in gain, known as the 'pulse height distribution,' and also to incorporate Gaussian baseline-noise voltage. Agreement with several experiments is shown to be excellent.

Proceedings of SPIE, May 28, 1999

Direct-detection laser radars can measure the range and the intensity returns from a target, with... more Direct-detection laser radars can measure the range and the intensity returns from a target, with or without clutter, for each part of the target resolved in angle by the optical system. Because the ladar's angular resolution is in micro-radians, there are generally at least a few angular pixels 'on target.' In addition, for narrow pulse (approximately 1 ns) ladar systems, there may be ten or so sequential intensity measurements in range per pixel as the laser pulse propagates down the target's surface. The output image is, therefore, potentially a three dimensional 'cube' of intensity measurements and quantized in the range axis by the range-bin size or 'voxel' size. This is known as 'range resolved angle-angle-intensity' ladar. In a previous paper we transformed this 3D-matrix image into the spatial-frequency domain using 3D- Fourier transforms and followed conventional 2D template correlation techniques to perform target recognition and identification. During this previous study, it was noted that the 2D range-bins could be placed in sequence and 2D filtering used on these synthetic images. Results of 3D and 2D-sequence target correlators using the 'joint transform correlator,' 'the inverse filter,' the 'phase-only matched-filter,' the 'binary phase-only filter,' and the classical 'matched filter' are presented here. Far-field test data using conical shaped targets are used to study the 3D and 2D correlators, and the effects of laser speckle are discussed. Recent developments in negative-binomial driven shot- noise effects in range-resolved direct-detection ladar are reviewed as well. These 3D or 2D-sequence template correlators may supplement or refine less computationally intensive algorithms such as total signal; range-extent; x-z, y-z, and x-y plane image centroid estimation; and image moments.

Proceedings of SPIE, Aug 1, 1991

The layered-sphere volumetric backscatter coefficient is examined for possibly enhancing the esti... more The layered-sphere volumetric backscatter coefficient is examined for possibly enhancing the estimates of the aerosol component distributions and their physical parameters with examples utilizing a coherent Lidar at 10.6 microns. It is found that at this wavelength alumina particles coated with soot, water, or sulfuric acid may exhibit greatly reduced backscattering due to destructive interference of the reflected waves plus guided wave action in the absorbing layer. Also, the layered-sphere calculations easily reduce to solid-sphere calculations as needed.

IEEE Journal of Quantum Electronics, Sep 1, 1977

Waveform 10 psec 1,2,4 msec pulse Typical transmitted Pulse repetition Duty cycle .05 .25 Minimum... more Waveform 10 psec 1,2,4 msec pulse Typical transmitted Pulse repetition Duty cycle .05 .25 Minimum detectable 3 dB beamwidth 10 prad 10 prad Typical operating range 5-20 km 1OoQ km Typical Doppler shift 0-2 MHz 0-1200 MHz Target 3 cm retroreflector 3.8 cm retroreflector peak power 10-IO0 pw 400 W frequency 4150Jsec 250, 125, 62.5Jsec , power 10-19 w , m , IO-19 W / H~-___ retro-reflector and the transmitted power was in the 10-50 pwatt region. Satellite tracking has been carried out on a 3.8 cm retroreflector installed on a geodetic satellite, GEOS-111. Continuous tracking has been accomplished at ranges to 1200 km and Doppler shifts as high as lo00 MHz. Modifications in the receiver, tracking servos, and software have been made and experiments are underway which will provide additional results to be presented. 9.6 A 10.6 pm Radar Fast Frame Rate Imaging System (! u~Y t d) .

Proceedings of SPIE, Jun 9, 2014

Atmospheric turbulence produces intensity modulation or "scintillation" effects on both... more Atmospheric turbulence produces intensity modulation or "scintillation" effects on both on the outward laser-mode path and on the return backscattered radiation path. These both degrade laser radar (ladar) target acquisition, ranging, imaging, and feature estimation. However, the finite sized objects create scintillation averaging on the outgoing path and the finite sized telescope apertures produce scintillation averaging on the return path. We expand on previous papers going to moderate to strong turbulence cases by starting from a 20kft altitude platform and propagating at 0° elevation (with respect to the local vertical) for 100km range to a 1 m diameter diffuse sphere. The outward scintillation and inward scintillation effects, as measured at the focal plane detector array of the receiving aperture, will be compared. To eliminate hard-body surface speckle effects in order to study scintillation, Goodman's M-parameter is set to 106 in the analytical equations and the non-coherent imaging algorithm is employed in Monte Carlo realizations. The analytical equations of the signal-to-noise ratio (SNRp), or mean squared signal over a variance, for a given focal plane array pixel window of interest will be summarized and compared to Monte Carlo realizations of a 1m diffuse sphere.

Proceedings of SPIE, Jun 9, 2014

Atmospheric turbulence produces intensity modulation or "scintillation" effects on both... more Atmospheric turbulence produces intensity modulation or "scintillation" effects on both on the outward laser-mode path and on the return backscattered radiation path. These both degrade laser radar (ladar) target acquisition, ranging, imaging, and feature estimation. However, the finite sized objects create scintillation averaging on the outgoing path and the finite sized telescope apertures produce scintillation averaging on the return path. We expand on previous papers going to moderate to strong turbulence cases by starting from a 20kft altitude platform and propagating at 0° elevation (with respect to the local vertical) for 100km range to a 1 m diameter diffuse sphere. The outward scintillation and inward scintillation effects, as measured at the focal plane detector array of the receiving aperture, will be compared. To eliminate hard-body surface speckle effects in order to study scintillation, Goodman's M-parameter is set to 106 in the analytical equations and the non-coherent imaging algorithm is employed in Monte Carlo realizations. The analytical equations of the signal-to-noise ratio (SNRp), or mean squared signal over a variance, for a given focal plane array pixel window of interest will be summarized and compared to Monte Carlo realizations of a 1m diffuse sphere.

Proceedings of SPIE, Feb 18, 1989

Shorter wavelength lasers have advantages over longer wavelength lasers due to their narrower bea... more Shorter wavelength lasers have advantages over longer wavelength lasers due to their narrower beam divergence angles and larger Doppler frequency shifts. However these potential advantages may not always be useable since they pose stringent requirements on beam pointer/tracker accuracies and on the laser gain medium optical distortions (spatially and temporally). Wavelength scaling equations are discussed which numerically show these advantages and limitations. Both coherent and non-coherent systems are evaluated, but the main emphasis is on coherent systems. The advantages of shorter wavelengths are often not as great as initially perceived. The wavelength variation of target cross section and the reflected laser speckle pattern are discussed. Single speckle-lobe detection imposes wavelength dependent limits on the receiver aperture. Speckle pattern rotation and translation puts limits on coherent detection times vs. wavelength, but velocity resolution is unchanged with wavelength. Laser propagation through the atmosphere is briefly reviewed for various laser wavelengths. The "maturity" and "applicability" of laser technology is discussed as a function of laser wavelength.

Proceedings of SPIE, Sep 8, 2004

The signal-to-noise power ratio parameter of coherent ladar systems operating within the atmosphe... more The signal-to-noise power ratio parameter of coherent ladar systems operating within the atmosphere and including atmospheric scintillation effects is modeled. Previously published round-trip geometry ladar data of the variance of the normalized-irradiance as a function of the one-way path integral Rytov parameter are utilized to estimate a signal-tonoise power ratio. However, these data were taken in the strong signal case where local-oscillator-laser noise was negligible. A model is proposed to combine the local-oscillator-laser produced noise, a zero-mean wideband-Gaussian random process corresponding to normal coherent ladar operation, with the scintillation produced by round-trip turbulence based on a calculation of the one-way path-integral Rytov parameter. Close agreement with Shapiro's 1981 analysis is found, provided one modifies the Shapiro formulation to account for scintillation saturation.

Proceedings of SPIE, May 1, 2012

A methodology for laser radar / ladar imaging through atmospheric turbulence is studied for targe... more A methodology for laser radar / ladar imaging through atmospheric turbulence is studied for target feature extraction, acquisition, tracking, identification, etc. The procedure follows sequentially by (1) laser-mode propagation through the outward atmospheric path, which is modeled by using multiple turbulence phase-screens; (2) the propagated laser mode illuminates a target which is modeled using multiple facets; and (3) simultaneously, or near simultaneously, the return path turbulence effects are modeled by a reverse order Cn 2(h), Lo, and lo set of phase-screens assuming a plane-wave. This return path amplitude & phase screen is then used to create a pupil plus atmospheric effects impulse-response which is used to (4) accurately construct the image of a diffuse target on the detector focal plane array using conventional Fourier optics. Agreement of both the outward and the return path phase-screen matrices with their respective analytical turbulence parameters, which are independently computed, is shown. The Fourier optics construction process of the target's image is reviewed, and typical diffuse target images of facet model objects are presented illustrating scintillation and speckle effects. The images may then be used in algorithm development for a specific system performance determination.

Proceedings of SPIE, Sep 13, 2004

Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating... more Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating surface can estimate the target's piston-mode displacement motion from the target's Doppler produced frequency spectrum. We review recent work showing that a newly developed joint time-frequency transform algorithm is superior to older joint time-frequency transforms, the common short-time-Fourier transform (spectrogram) algorithm, and other elementary spectral estimation algorithms for resolving the target's spectra. In this paper we extend these approaches when the ladar is observing an unresolved (smaller than the incident laser mode) piston-mode vibrating object situated on the ground. Because the target is smaller than the laser spot, the surrounding ground produces a narrow-band constant frequency "clutter" signal at the baseband frequency. We show that a recently developed "sech-window" joint time-frequency transform is superior to other algorithms for separating the frequency modulated target piston motion signal from the narrow-band ground return. The analysis in this case includes a "signal-to-clutter ratio" (SCR) parameter variation as well as a "carrier-to-noise ratio" (CNR), or target signal strength to LO-laser noise strength, parameter variation.

Proceedings of SPIE, Apr 3, 2008

A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resol... more A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resolved Doppler and intensity (RRDI) or inverse synthetic aperture ladar (ISAR) imaging coherent laser radar, known as coherent "lidar" for optically thin targets. The poly-phase P4 ladar waveform and its RRDI images are described and compared with previous pulse-burst, linear-FM chirp pulse-compression, pseudo-random phase modulation waveforms, and several other waveforms which have not been utilized to date. A "dust cloud" has very many independently moving point scatterers with velocities that are approximately Gaussian randomly distributed in x,y,z with standard deviations of about 10% of the mean wind + aerosol velocity. This is contrary to a hard-target where the point scatterers are rigidly attached and moving together. The dust cloud produced speckle effects for the various ladar waveforms are compared. In addition, a reference set of four corner-cube retro-reflectors within the dust cloud further illustrates the differences in the various waveform capabilities and resolution.

Proceedings of SPIE, Sep 2, 2003

We examine the signal processing of both linear and sinusoidal frequency modulation (FM) coherent... more We examine the signal processing of both linear and sinusoidal frequency modulation (FM) coherent ladar returns from resolved and unresolved targets, which are spread in Doppler. The Doppler spread may be due to target spin, tumbling, or vibration as well as to the applied linear or sinusoidal-FM on the transmitted E-field. Monte Carlo realizations of the target surface random phasor reflector elements interact with the incident Efield producing laser speckle, and the speckled returns are analyzed in this study. The speckle signals are processed (1) using several spectrum (periodogram based) estimators, (2) the conventional “spectrogram” approach, and (3) ten joint time-frequency transforms (JTFT). We show that the Born-Jordan JTFT is superior to the other spectral estimators tested here in suppressing local oscillator laser noise and accurately estimating the target's spectrum for signal processing under speckle target return conditions pertaining to coherent laser radar. A new algorithm which sums particular pixels of the JTFT image is introduced and is shown to be much more robust in low CNR conditions than the JTFT maxima or JTFT centroid processing when utilizing the applied linear or sinusoidal-FM modulation waveform.

Proceedings of SPIE, Sep 5, 2000

A simple analytical model of a laser radar's subtended irradiance probability-density-functio... more A simple analytical model of a laser radar's subtended irradiance probability-density-function has been developed for both direct detection and coherent detection laser radar. The vacuum speckle irradiance statistics are developed following Goodman's 'M parameter' treatment for direct detection ladar and also by setting the M-parameter equal to one (negative- exponential power statistics) for coherent laser radar. A 'turbulence M parameter' is then computed using the round-trip aperture averaging analyses of Gudimetla and Holmes based on the Rytov-variance parameter computation over an atmospheric path of interest. The 'vacuum M parameter' and the 'turbulence M parameter' are then combined to form an 'effective M parameter.' This effective M parameter is used in an analytically simple gamma distribution probability-density- function for the laser radar's subtended irradiance. We will show excellent agreement with the more analytically complicated two-parameter K-distribution from the literature. We will also indicate how one may include the turbulence scintillation in addition to the fundamental vacuum speckle, with increasing levels of turbulence to determine ladar performance.

Proceedings of SPIE, May 1, 2009

A facet model of a helicopter containing 35,000 facets is used to compare coherent ladar waveform... more A facet model of a helicopter containing 35,000 facets is used to compare coherent ladar waveform performance in precision and in resolution. The helicopter represents a convenient man made object for these tests. Several coherent ladar waveforms have been compared previously applying "range-resolved Doppler and intensity" (RRDI) or "inverse synthetic aperture ladar" (ISAR) algorithms in order to numerically construct an image of the target in slant-range and Doppler frequency spread. The targets are generally at large distances and are much smaller than the diffraction limited laser spot size or the diffraction limited detector's field-of-view. In this study we emphasize the "tangent-FM" waveform and review its performance relative to other waveforms. Note that thousands of facet models of interest are available on the internet and are usually low cost or even free. We also utilized a new "analytic signal" construction, recently published, for a small improvement in the final image quality.

NASA STI/Recon Technical Report N, Nov 5, 1986

Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling pre... more Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling previously established for two waveguides to a two dimensional array. In the theoretical portion of the program, two-dimensional array mode relative oscillator strengths (E-field distributions) were derived analytically for the first time. Fourier analysis of these array-modes indicated that almost an (nxm)2 increase (as for an array which is superimposed into one waveguide)in the far-field peak irradiance distribution would be achieved. The experimental program employed 1x7 and 2x3 arrays. Severe vacuum and materials problems were encountered with the 1x7 array. The 2x3 array achieved output powers of up to 8W per channel; on installation of ZnSe coupling windows the power decreased by an order of magnitude. Lasing could be achieved with all channels. No phase-locking was observed with either the 1x7 or 2x3 array for any of twenty different resonator configuration employed, including those using focussed and unfocussed grating. Folded resonator modes were found to dominate certain resonator configurations.

NASA STI/Recon Technical Report N, Nov 5, 1986

Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling pre... more Abstract : The purpose of this effort was to extend the principle of wavelength mode coupling previously established for two waveguides to a two dimensional array. In the theoretical portion of the program, two-dimensional array mode relative oscillator strengths (E-field distributions) were derived analytically for the first time. Fourier analysis of these array-modes indicated that almost an (nxm)2 increase (as for an array which is superimposed into one waveguide)in the far-field peak irradiance distribution would be achieved. The experimental program employed 1x7 and 2x3 arrays. Severe vacuum and materials problems were encountered with the 1x7 array. The 2x3 array achieved output powers of up to 8W per channel; on installation of ZnSe coupling windows the power decreased by an order of magnitude. Lasing could be achieved with all channels. No phase-locking was observed with either the 1x7 or 2x3 array for any of twenty different resonator configuration employed, including those using focussed and unfocussed grating. Folded resonator modes were found to dominate certain resonator configurations.

Proceedings of SPIE, May 19, 2015

Backscatter from atmospheric aerosols and molecular nitrogen and oxygen causes “clutter” noise in... more Backscatter from atmospheric aerosols and molecular nitrogen and oxygen causes “clutter” noise in direct detection ladar applications operating within the atmosphere. The backscatter clutter is more pronounced in multiple pulse, high PRF ladars where pulse-averaging is used to increase operating range. As more and more pulses are added to the wavetrain the backscatter increases. We analyze the imaging of a transmitted Gaussian laser-mode multi-pulse wave-train scatteried off of aerosols and molecules at the focal plane including angular-slew rate resulting from optical tracking, angular lead-angle, and bistatic-optics spatial separation. The defocused backscatter images, from those pulses closest to the receiver, are analyzed using a simple geometrical optics approximation. Methods for estimating the aerosol number density versus altitude and the volume backscatter coefficient of the aerosols are also discussed.

Proceedings of SPIE, Apr 17, 1995

Basing laser radar systems aboard aircraft provides capability for accurate tracking of ground, a... more Basing laser radar systems aboard aircraft provides capability for accurate tracking of ground, airborne, and ballistic missile targets from long range. The atmospheric effects of long propagation paths impact the performance of laser radar systems in two important ways -- molecular and aerosol extinction and optical turbulence. This paper provides quantitative assessment of the impact of these effects for laser radar wavelengths beyond 1.4 microns. The treatment of round-trip turbulence on direct detection systems is believed to be the first estimate of this effect. A more complete system analysis is underway and will be described in a forthcoming paper.

Proceedings of SPIE, Mar 1, 1974

Proceedings of SPIE, Sep 5, 2000

The number of photons returning from a target in a given time interval is a negative-binomially d... more The number of photons returning from a target in a given time interval is a negative-binomially distributed random variable. The resulting detected photon 'electron pulses' produced by a photomultiplier tube (PMT) photon-counting detector are also negative-binomially distributed per time bin with a reduced mean. These time distributed electron pulses are amplified and filtered by the receiver electronics, prior to digitization and signal processing. The voltage output pulse per individual photo-electron event is known as the 'impulse-response- function' of the detector and amplifier. The random summation of these voltage impulse-responses, as created by the negative-binomial photon arrival times and photo-electron creation, is the classical electronic 'shot-noise' random process. We derive the voltage probability density function of this 'negative-binomial driven shot-noise' random process following the stochastic process literature. We also show a technique to include PMT variations in gain, known as the 'pulse height distribution,' and also to incorporate Gaussian baseline-noise voltage. Agreement with several experiments is shown to be excellent.

Proceedings of SPIE, May 28, 1999

Direct-detection laser radars can measure the range and the intensity returns from a target, with... more Direct-detection laser radars can measure the range and the intensity returns from a target, with or without clutter, for each part of the target resolved in angle by the optical system. Because the ladar's angular resolution is in micro-radians, there are generally at least a few angular pixels 'on target.' In addition, for narrow pulse (approximately 1 ns) ladar systems, there may be ten or so sequential intensity measurements in range per pixel as the laser pulse propagates down the target's surface. The output image is, therefore, potentially a three dimensional 'cube' of intensity measurements and quantized in the range axis by the range-bin size or 'voxel' size. This is known as 'range resolved angle-angle-intensity' ladar. In a previous paper we transformed this 3D-matrix image into the spatial-frequency domain using 3D- Fourier transforms and followed conventional 2D template correlation techniques to perform target recognition and identification. During this previous study, it was noted that the 2D range-bins could be placed in sequence and 2D filtering used on these synthetic images. Results of 3D and 2D-sequence target correlators using the 'joint transform correlator,' 'the inverse filter,' the 'phase-only matched-filter,' the 'binary phase-only filter,' and the classical 'matched filter' are presented here. Far-field test data using conical shaped targets are used to study the 3D and 2D correlators, and the effects of laser speckle are discussed. Recent developments in negative-binomial driven shot- noise effects in range-resolved direct-detection ladar are reviewed as well. These 3D or 2D-sequence template correlators may supplement or refine less computationally intensive algorithms such as total signal; range-extent; x-z, y-z, and x-y plane image centroid estimation; and image moments.

Proceedings of SPIE, Aug 1, 1991

The layered-sphere volumetric backscatter coefficient is examined for possibly enhancing the esti... more The layered-sphere volumetric backscatter coefficient is examined for possibly enhancing the estimates of the aerosol component distributions and their physical parameters with examples utilizing a coherent Lidar at 10.6 microns. It is found that at this wavelength alumina particles coated with soot, water, or sulfuric acid may exhibit greatly reduced backscattering due to destructive interference of the reflected waves plus guided wave action in the absorbing layer. Also, the layered-sphere calculations easily reduce to solid-sphere calculations as needed.

IEEE Journal of Quantum Electronics, Sep 1, 1977

Waveform 10 psec 1,2,4 msec pulse Typical transmitted Pulse repetition Duty cycle .05 .25 Minimum... more Waveform 10 psec 1,2,4 msec pulse Typical transmitted Pulse repetition Duty cycle .05 .25 Minimum detectable 3 dB beamwidth 10 prad 10 prad Typical operating range 5-20 km 1OoQ km Typical Doppler shift 0-2 MHz 0-1200 MHz Target 3 cm retroreflector 3.8 cm retroreflector peak power 10-IO0 pw 400 W frequency 4150Jsec 250, 125, 62.5Jsec , power 10-19 w , m , IO-19 W / H~-___ retro-reflector and the transmitted power was in the 10-50 pwatt region. Satellite tracking has been carried out on a 3.8 cm retroreflector installed on a geodetic satellite, GEOS-111. Continuous tracking has been accomplished at ranges to 1200 km and Doppler shifts as high as lo00 MHz. Modifications in the receiver, tracking servos, and software have been made and experiments are underway which will provide additional results to be presented. 9.6 A 10.6 pm Radar Fast Frame Rate Imaging System (! u~Y t d) .

Proceedings of SPIE, Jun 9, 2014

Atmospheric turbulence produces intensity modulation or "scintillation" effects on both... more Atmospheric turbulence produces intensity modulation or "scintillation" effects on both on the outward laser-mode path and on the return backscattered radiation path. These both degrade laser radar (ladar) target acquisition, ranging, imaging, and feature estimation. However, the finite sized objects create scintillation averaging on the outgoing path and the finite sized telescope apertures produce scintillation averaging on the return path. We expand on previous papers going to moderate to strong turbulence cases by starting from a 20kft altitude platform and propagating at 0° elevation (with respect to the local vertical) for 100km range to a 1 m diameter diffuse sphere. The outward scintillation and inward scintillation effects, as measured at the focal plane detector array of the receiving aperture, will be compared. To eliminate hard-body surface speckle effects in order to study scintillation, Goodman's M-parameter is set to 106 in the analytical equations and the non-coherent imaging algorithm is employed in Monte Carlo realizations. The analytical equations of the signal-to-noise ratio (SNRp), or mean squared signal over a variance, for a given focal plane array pixel window of interest will be summarized and compared to Monte Carlo realizations of a 1m diffuse sphere.

Proceedings of SPIE, Jun 9, 2014

Atmospheric turbulence produces intensity modulation or "scintillation" effects on both... more Atmospheric turbulence produces intensity modulation or "scintillation" effects on both on the outward laser-mode path and on the return backscattered radiation path. These both degrade laser radar (ladar) target acquisition, ranging, imaging, and feature estimation. However, the finite sized objects create scintillation averaging on the outgoing path and the finite sized telescope apertures produce scintillation averaging on the return path. We expand on previous papers going to moderate to strong turbulence cases by starting from a 20kft altitude platform and propagating at 0° elevation (with respect to the local vertical) for 100km range to a 1 m diameter diffuse sphere. The outward scintillation and inward scintillation effects, as measured at the focal plane detector array of the receiving aperture, will be compared. To eliminate hard-body surface speckle effects in order to study scintillation, Goodman's M-parameter is set to 106 in the analytical equations and the non-coherent imaging algorithm is employed in Monte Carlo realizations. The analytical equations of the signal-to-noise ratio (SNRp), or mean squared signal over a variance, for a given focal plane array pixel window of interest will be summarized and compared to Monte Carlo realizations of a 1m diffuse sphere.

Proceedings of SPIE, Feb 18, 1989

Shorter wavelength lasers have advantages over longer wavelength lasers due to their narrower bea... more Shorter wavelength lasers have advantages over longer wavelength lasers due to their narrower beam divergence angles and larger Doppler frequency shifts. However these potential advantages may not always be useable since they pose stringent requirements on beam pointer/tracker accuracies and on the laser gain medium optical distortions (spatially and temporally). Wavelength scaling equations are discussed which numerically show these advantages and limitations. Both coherent and non-coherent systems are evaluated, but the main emphasis is on coherent systems. The advantages of shorter wavelengths are often not as great as initially perceived. The wavelength variation of target cross section and the reflected laser speckle pattern are discussed. Single speckle-lobe detection imposes wavelength dependent limits on the receiver aperture. Speckle pattern rotation and translation puts limits on coherent detection times vs. wavelength, but velocity resolution is unchanged with wavelength. Laser propagation through the atmosphere is briefly reviewed for various laser wavelengths. The "maturity" and "applicability" of laser technology is discussed as a function of laser wavelength.

Proceedings of SPIE, Sep 8, 2004

The signal-to-noise power ratio parameter of coherent ladar systems operating within the atmosphe... more The signal-to-noise power ratio parameter of coherent ladar systems operating within the atmosphere and including atmospheric scintillation effects is modeled. Previously published round-trip geometry ladar data of the variance of the normalized-irradiance as a function of the one-way path integral Rytov parameter are utilized to estimate a signal-tonoise power ratio. However, these data were taken in the strong signal case where local-oscillator-laser noise was negligible. A model is proposed to combine the local-oscillator-laser produced noise, a zero-mean wideband-Gaussian random process corresponding to normal coherent ladar operation, with the scintillation produced by round-trip turbulence based on a calculation of the one-way path-integral Rytov parameter. Close agreement with Shapiro's 1981 analysis is found, provided one modifies the Shapiro formulation to account for scintillation saturation.

Proceedings of SPIE, May 1, 2012

A methodology for laser radar / ladar imaging through atmospheric turbulence is studied for targe... more A methodology for laser radar / ladar imaging through atmospheric turbulence is studied for target feature extraction, acquisition, tracking, identification, etc. The procedure follows sequentially by (1) laser-mode propagation through the outward atmospheric path, which is modeled by using multiple turbulence phase-screens; (2) the propagated laser mode illuminates a target which is modeled using multiple facets; and (3) simultaneously, or near simultaneously, the return path turbulence effects are modeled by a reverse order Cn 2(h), Lo, and lo set of phase-screens assuming a plane-wave. This return path amplitude & phase screen is then used to create a pupil plus atmospheric effects impulse-response which is used to (4) accurately construct the image of a diffuse target on the detector focal plane array using conventional Fourier optics. Agreement of both the outward and the return path phase-screen matrices with their respective analytical turbulence parameters, which are independently computed, is shown. The Fourier optics construction process of the target's image is reviewed, and typical diffuse target images of facet model objects are presented illustrating scintillation and speckle effects. The images may then be used in algorithm development for a specific system performance determination.

Proceedings of SPIE, Sep 13, 2004

Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating... more Coherent laser radars observing a resolved (larger than the incident laser mode) target vibrating surface can estimate the target's piston-mode displacement motion from the target's Doppler produced frequency spectrum. We review recent work showing that a newly developed joint time-frequency transform algorithm is superior to older joint time-frequency transforms, the common short-time-Fourier transform (spectrogram) algorithm, and other elementary spectral estimation algorithms for resolving the target's spectra. In this paper we extend these approaches when the ladar is observing an unresolved (smaller than the incident laser mode) piston-mode vibrating object situated on the ground. Because the target is smaller than the laser spot, the surrounding ground produces a narrow-band constant frequency "clutter" signal at the baseband frequency. We show that a recently developed "sech-window" joint time-frequency transform is superior to other algorithms for separating the frequency modulated target piston motion signal from the narrow-band ground return. The analysis in this case includes a "signal-to-clutter ratio" (SCR) parameter variation as well as a "carrier-to-noise ratio" (CNR), or target signal strength to LO-laser noise strength, parameter variation.

Proceedings of SPIE, Apr 3, 2008

A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resol... more A dust or aerosol cloud represents a convenient target to examine the capabilities of range-resolved Doppler and intensity (RRDI) or inverse synthetic aperture ladar (ISAR) imaging coherent laser radar, known as coherent "lidar" for optically thin targets. The poly-phase P4 ladar waveform and its RRDI images are described and compared with previous pulse-burst, linear-FM chirp pulse-compression, pseudo-random phase modulation waveforms, and several other waveforms which have not been utilized to date. A "dust cloud" has very many independently moving point scatterers with velocities that are approximately Gaussian randomly distributed in x,y,z with standard deviations of about 10% of the mean wind + aerosol velocity. This is contrary to a hard-target where the point scatterers are rigidly attached and moving together. The dust cloud produced speckle effects for the various ladar waveforms are compared. In addition, a reference set of four corner-cube retro-reflectors within the dust cloud further illustrates the differences in the various waveform capabilities and resolution.

Proceedings of SPIE, Sep 2, 2003

We examine the signal processing of both linear and sinusoidal frequency modulation (FM) coherent... more We examine the signal processing of both linear and sinusoidal frequency modulation (FM) coherent ladar returns from resolved and unresolved targets, which are spread in Doppler. The Doppler spread may be due to target spin, tumbling, or vibration as well as to the applied linear or sinusoidal-FM on the transmitted E-field. Monte Carlo realizations of the target surface random phasor reflector elements interact with the incident Efield producing laser speckle, and the speckled returns are analyzed in this study. The speckle signals are processed (1) using several spectrum (periodogram based) estimators, (2) the conventional “spectrogram” approach, and (3) ten joint time-frequency transforms (JTFT). We show that the Born-Jordan JTFT is superior to the other spectral estimators tested here in suppressing local oscillator laser noise and accurately estimating the target's spectrum for signal processing under speckle target return conditions pertaining to coherent laser radar. A new algorithm which sums particular pixels of the JTFT image is introduced and is shown to be much more robust in low CNR conditions than the JTFT maxima or JTFT centroid processing when utilizing the applied linear or sinusoidal-FM modulation waveform.

Proceedings of SPIE, Sep 5, 2000

A simple analytical model of a laser radar's subtended irradiance probability-density-functio... more A simple analytical model of a laser radar's subtended irradiance probability-density-function has been developed for both direct detection and coherent detection laser radar. The vacuum speckle irradiance statistics are developed following Goodman's 'M parameter' treatment for direct detection ladar and also by setting the M-parameter equal to one (negative- exponential power statistics) for coherent laser radar. A 'turbulence M parameter' is then computed using the round-trip aperture averaging analyses of Gudimetla and Holmes based on the Rytov-variance parameter computation over an atmospheric path of interest. The 'vacuum M parameter' and the 'turbulence M parameter' are then combined to form an 'effective M parameter.' This effective M parameter is used in an analytically simple gamma distribution probability-density- function for the laser radar's subtended irradiance. We will show excellent agreement with the more analytically complicated two-parameter K-distribution from the literature. We will also indicate how one may include the turbulence scintillation in addition to the fundamental vacuum speckle, with increasing levels of turbulence to determine ladar performance.

Proceedings of SPIE, May 1, 2009

A facet model of a helicopter containing 35,000 facets is used to compare coherent ladar waveform... more A facet model of a helicopter containing 35,000 facets is used to compare coherent ladar waveform performance in precision and in resolution. The helicopter represents a convenient man made object for these tests. Several coherent ladar waveforms have been compared previously applying "range-resolved Doppler and intensity" (RRDI) or "inverse synthetic aperture ladar" (ISAR) algorithms in order to numerically construct an image of the target in slant-range and Doppler frequency spread. The targets are generally at large distances and are much smaller than the diffraction limited laser spot size or the diffraction limited detector's field-of-view. In this study we emphasize the "tangent-FM" waveform and review its performance relative to other waveforms. Note that thousands of facet models of interest are available on the internet and are usually low cost or even free. We also utilized a new "analytic signal" construction, recently published, for a small improvement in the final image quality.