An automated video enhancement technique capable of image fusion from a stream of randomly-distorted images of a
still scene is presented in this paper. The technique is based on the "lucky-region" fusion (LRF) approach and aims to
improve locally the image quality according to the following steps: (1) for each image of the video stream an image
quality map (IQM) which characterizes locally the image quality is computed, (2) each IQM is compared to that of the
current fused image leading to the selection of best quality regions (the "lucky-regions"), and (3) the selected regions are
merged into the fused video stream. While the LRF approach succeeds in producing images with significantly improved
image quality compared to the source images, its performance depends on the imaging conditions and requires
adjustment of its fusion parameter - the fusion kernel size - in order to adapt to an evolving environment (e.g. a
turbulent atmosphere). Parameter selection was so far performed manually using a trial-and-error approach which causes
the technique to be impractical for a real world implementation. The automated LRF technique presented is relaxed from
this requirement and selects automatically the fusion parameter based on the analysis of the source images making it
more suitable for practical systems. The improved LRF technique is applied to imaging through atmospheric turbulence
for various imaging conditions and scenes of interest. In each case automatically-fused video streams demonstrate
increases in image quality comparable to that obtained with manual selection of the fusion parameter.
An imaging enhancement technique capable of mitigating the effect of atmospheric turbulence on wide field-of-view
images is presented. The method is based on the local information fusion from a set of short-exposure anisoplanatic
images. Since anisoplanatism affects short-exposure images locally, the synthetic imaging algorithm uses local image
quality information. Pre-processing of the source data and use of a composed image quality metric are considered. The
synthetic imaging technique is tested on experimental data. The synthesized images show an improvement in image
quality compared to the original set of images.
Conventional tracking systems measure time-space-position data and collect imagery to quantify the flight dynamics of
tracked targets. A major obstacle that severely impacts the accuracy of the target characterization is atmospheric
turbulence induced distortion of the tracking laser beam and imagery degradations. Tracking occurs in a continuously
changing atmosphere resulting in rapid variations in the tracking laser beam and distorted imagery. These atmospheric
effects, combined with other degradation effects such as measurement system motion, defocus blur, and spatially varying
noise, severely limit the viability and accuracy of many tracking and imagery-based analysis methods. In 2007, using a
high speed sled test, the feasibility of quantifying flight dynamics with stereo laser tracking and multi-video imagery was
demonstrated. The technique acquires stereo views (two or more) of a moving test article that has an applied random
speckle (dot) pattern painted on the surface to provide unique tracking points. The stereo views are reconciled via
coordinate transformations and correlation of the transformed images. The 2007 results demonstrated that dual laser
tracker data can be used to update camera calibration data for stereo imaging to extend the image correlation approach to
moving field of view applications such as missile tracking and missile performance characterization, e.g., attitude
measurements. However, these results were predominantly qualitative in nature, focusing on the degree of correlation.
This paper will present quantitative results from 2008 outdoor centrifuge tests and assess the digital image correlation
accuracy for time varying attitude and position measurements.
An array of micromirrors can be used to correct the wavefront aberrations due to atmospheric turbulence. A simple method is presented for estimating the number of piston-only micromirrors needed to correct the seeing. We also compute how many piston-tip-tilt micromirrors are required. The three-actuator micromirrors are found to produce a more efficient solution, requiring 4X fewer actuators for the same improvement in the Strehl ratio.
Commercial ranging systems (both beam modulation and pulsed time of flight systems) have an operating range and
accuracy far below the needs for moving target system qualification testing and model validation. A new, eye-safe,
long operating range, accurate (order of cm) ranging system must be developed. The most feasible approach to
achieve this capability requires an ultrashort pulse laser system in conjunction with time-of-flight measurement
methods. Accordingly, the Institute of Applied Physics and Sandia National Laboratories are developing an
advanced ranging system for use in Sandia's mobile laser tracker for quantification of the flight dynamics of high
speed moving targets. Key to this development is a new laser. This paper presents a new picosecond Raman laser
capable of range measurements to 50 km with 1 cm accuracy in the presence of atmospheric turbulence.
We present the development of a novel technique for numerical simulation and analysis of wide field-of-view (FOV)
incoherent and anisoplanatic imaging of an object through volume turbulence. This technique is based on the recently
developed brightness function method [J. Opt. Soc. Am. A, v. 22, p. 126 (2005)]. We present computer simulation
results demonstrating the anisoplanatic turbulence effects on an object image quality.
Conventional tracking systems measure time-space-position data and collect imagery to quantify the flight dynamics of
tracked targets. One of the major obstacles that severely impacts the accuracy and fidelity of the target characterization is
atmospheric turbulence induced distortions of the tracking laser beam at the target surface and imagery degradations.
Tracking occurs in a continuously changing atmosphere resulting in rapid variations in the tracking laser beam and
distorted imagery. These atmospheric effects, in combination with other sources of degradation, such as measurement
system motions (e.g. vibration/jitter), defocus blur, and spatially varying noise, severely limit the useful and accuracy of
many tracking and analysis methods.
This paper discusses the viability of employing stereo image correlation methods for high speed moving target
characterization through atmospheric turbulence. Stereo imaging methods have proven effective in the laboratory for
quantifying temporally and spatially resolved 3D motions across a target surface. This technique acquires stereo views
(two or more) of a test article that has an applied random speckled (dot) pattern painted on the surface to provide
trackable features on the entire target surface. The stereo views are reconciled via coordinate transformations and
correlation of the transformed images. The principle limitations of this method have been the need for clean imagery and
fixed camera positions and orientations. However, recent field tests have demonstrated that these limitations can be
overcome to provide a new method for quantifying flight dynamics with stereo laser tracking and multi-video imagery in
the presence of atmospheric turbulence.
The paper suggests a model for predicting the behavior of the optical characteristics of a medium that determine the character
of laser beam propagation in the atmosphere. These are first of all the refractive index and the refractive-index-structure
parameter as well as the wind velocity, kinetic turbulence energy, dissipation energy speed and other meteorological
parameters that are important in the laser propagation problem. The prediction of the refractive index and the refractive-indexstructure
parameter is based on the known equations of the theory of wave propagation in a turbulent atmosphere and a
mathematical model for short-range forecast of evolution of local meteorology and turbulent structure of the atmospheric
boundary layer (ABL).
The error caused by atmospheric turbulence, in determining the orientation angle of an object (a series of reflectors) has
been studied. The orientation angle was determined by studying the image of the object. Numerical modeling was
performed involving construction of the image of a series of reflectors as if they were observed through a turbulent
medium, calculation of the coordinates of reflector mass centers, finding of the line closest to the reflector mass centers,
and determination of its slope angle. Variance of the slope angle fluctuations is calculated.
The paper considers the error caused by atmospheric turbulence, in determining the motion speed of an object by using
its successive images recorded on a matrix of a digital camera. Numerical modeling of the image of a moving object in
successive time moments is performed. Fluctuation variance of the image mass centre affecting the measurement error
is calculated. Error dependences on the distance to the object and path slope angle are obtained for different turbulence
models. Considered are the situations, when the angular displacement of the object between two immediate shots of the digital camera is greater than the isoplanatism angle as well as the situations when the angular displacement is smaller
than this angle.
The energy and statistical characteristics of laser radiation reflected from an infinite surface in the form of an array of
single retroreflectors have been investigated. The study of the reflecting properties of such a surface involved the
calculation of the coherence function of the radiation in the reflection plane. Rigorous and high-accuracy approximate
expressions have been obtained for this characteristic.
The intensity in the far zone and the coherence function of the reflected radiation at an arbitrary distance from the
surface have been calculated. Approximate equations have been derived for these characteristics of the radiation. The
results of numerical simulation by the Monte Carlo technique have been compared with the rigorous and approximate
calculations. It has been shown that in the most significant cases the approximate equations proposed give a deviation
within 5% from the rigorous ones and from the results of averaging over numerical realizations.
The approximate equations obtained have been used to solve the problem of radiation propagation along sensing paths,
including the forward propagation through the turbulent atmosphere, reflection, and backward propagation.
Photon budget analysis for laser target tracking systems under atmospheric turbulence conditions is performed in the paper. This analysis includes evaluations of the effects of molecular and aerosol absorption/scattering at various propagation distances and tracking angles for the following laser tracking wavelengths: 0.53 micrometers, 1.06 micrometers and 1.55 micrometers and evaluations of tracking beam/target interaction (target light scattering, target-induced coherence degradation, influence of target shape) for targets with rough surfaces, retro-reflective tape, and a single retro-reflector.
Numerical modeling of optical wave propagation in atmospheric turbulence is traditionally performed by using the so-called "split" - operator method, where the influence of the propagation medium's refractive index inhomogeneities is accounted for only within a set of infinitely narrow phase distorting layers (phase screens). These phase screens are generated on a numerical grid of finite size, which corresponds to a rather narrow slice (spatial area) of atmospheric turbulence. In several important applications including laser target tracking, adaptive optics, and atmospheric imaging optical system performance depends on atmospheric turbulence within an extended area that significantly exceeds the area associated with the numerical grid. In this paper we discuss methods that allow the generation of a
family of long (including infinitely long) phase screens representing an extended (in one direction) area of atmospheric turbulence-induced phase distortions. This technique also allows the generation of long phase screens with spatially inhomogeneous statistical characteristics. It can be applied to the numerical analysis of laser tracking and directed energy systems over long target trajectories.
TrackEye is a film digitization and target tracking system that offers the potential for quantitatively measuring the dynamic state variables (e.g., absolute and relative position, orientation, linear and angular velocity/acceleration, spin rate, trajectory, angle of attack, etc.) for moving objects using captured single or dual view image sequences. At the heart of the system is a set of tracking algorithms that automatically find and quantify the location of user selected image details such as natural test article features or passive fiducials that have been applied to cooperative test articles. This image position data is converted into real world coordinates and rates with user specified information such as the image scale and frame rate. Though tracking methods such as correlation algorithms are typically robust by nature, the accuracy and suitability of each TrackEye tracking algorithm is in general unknown even under good imaging conditions. The challenges of optimal algorithm selection and algorithm performance/measurement uncertainty are even more significant for long range tracking of high-speed targets where temporally varying atmospheric effects degrade the imagery. This paper will present the preliminary results from a controlled test sequence used to characterize the performance of the TrackEye tracking algorithm suite.
Historically tracking systems have provided limited quantitative data such as approximate range, speed, and trajectory. Today's tracking systems are now being tasked with accurately quantifying a broader range of dynamic state variables (e.g., absolute and relative position, orientation, linear and angular velocity/acceleration, spin rate, trajectory, angle of attack, angle of impact) for high-speed test articles. This information is needed to demonstrate that the required test conditions are achieved, to develop, validate, and apply predictive models, and to document a system's response to a test environment. Few existing and emerging optical tracking methods accurately provide the dynamic state variables. Even fewer quantify the measurement uncertainty. Past measurement error estimates have been either qualitative or lacked the rigor needed to accurately validate and apply predictive models. This presentation will discuss tracking options and approaches for characterizing tracking measurement uncertainty.
Investigations of the dynamics of turbulent characteristics were carried out for different tracking paths based on theoretical equations. A multi-screen model and single-screen one for turbulent atmosphere have been constructed for numerical simulation of laser beam propagation along atmospheric paths within the framework of the paraxial approximation. These models are suitable for simulation of the propagation along both homogeneous and inhomogeneous paths. Within this model, the Fried radius, the scintillation index, the effective beam radius, and the coherence length of radiation were calculated. The values obtained in the numerical experiment were compared with those calculated analytically.
This paper evaluates equivalent sphere approaches for modeling nonspherical aerosols in MTFs calculations. A Monte Carlo simulation is used to calculate the image of point source in a scattering medium. The MTF is then found using a 2-D FFT on the resulting image (power distribution). The aerosol phase functions are computed using Mie theory for spherical particles and the Method of Extended Boundary Conditions for nonspherical particles. Spheres with radii determined by the nonspherical aerosol volume, surface area, orientation averaged radius, semi-minor axis length, and semi-major axis length are considered. Sample MTF results are presented for a 2:1 axial ratio prolate spheroid at a wavelength of 9.2 micrometers .
Aerosol scattering produces image degradation effects which can be characterized by the MTF. This paper describes a technique for calculating MTFs for atmospheres containing nonspherical particles. The approach uses the extended boundary condition method and a Monte Carlo simulation to model a scattering atmosphere. Model MTF results for 8.0 and 9.2 microns are presented for media containing spheroidal particles.
The residual image is analyzed to determine a constraint which regularizes the ill-posed least squares image restoration problem. The energy in the residual image is constrained at a level which depends on the noise statistics, image degradation, and restoration method. This constraint is applied individually to different image subregions, to find different regularizations appropriate in each subregion. This defines a spatially variant restoration method, even for a spatially invariant image degradation. Least squares image restoration methods using this constraint are applied to an artificial image which has been degraded by simulated long-exposure atmospheric turbulence and random noise. Quantitative analysis of the restored image shows significant improvement with this constraint, in comparison to the usual constraint on residual energy which depends only on noise statistics.
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