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Showing papers by "Norman S. Kopeika published in 1996"


Proceedings ArticleDOI
14 Nov 1996
TL;DR: In this paper, the authors proposed a method to identify important parameters with which to characterize the PSF of the blur, given only the blurred image itself, based on the concept that image characteristics along the direction of motion are different than the characteristics in other directions.
Abstract: A difficult problem in imaging systems is degradation of images caused by motion. This problem is common when the imaging system is in moving vehicles such as tanks or planes and even when the camera is held by human hands. For correct restoration of the degraded image we need to know the point spread function (PSF) of the blurring system. In this paper we propose a method to identify important parameters with which to characterize the PSF of the blur, given only the blurred image itself. A first step of this method has been suggested in a former paper where only the blur extent parameter was considered. The identification method here is based on the concept that image characteristics along the direction of motion are different than the characteristics in other directions. Depending on the PSF shape, the homogeneity and the smoothness of the blurred image in the motion direction are higher than in other directions. Furthermore, in the motion direction correlation exists between the pixels forming the blur of the original unblurred objects. The method proposed here identifies the direction and the extent of the PSF of the blur and evaluates its shape which depends on the type of motion during the exposure. Correct identification of the PSF parameters permits fast high resolution restoration of the blurred image.

89 citations


Proceedings ArticleDOI
18 Oct 1996
TL;DR: A mathematical model including theperformance of the communication system as a function of the performance of the tracking system is derived and from this model the optimum transmitter telescope gain is derived.
Abstract: The basic configuration of free space satellite optical communication includes a transmitter and a receiver. The transmitter satellite must point the optical information beam to the receiver satellite in order to establish communication. An important aspect in satellite optical communication is to obtain minimum bit error rate using minimum power. This aim can be achieved with very small transmitter beam divergence angles. The disadvantages of too narrow a divergence angle are that the transmitter beam may sometimes miss the receiver satellite due to pointing vibrations, and that the transmitter optics aperture required is large and expensive. The optimum value of the received power as a function of the pointing vibration displacement determines the optimum bean divergence angle. The performance of the tracking system determines the amplitude limits of the vibrations of the transmitter beam in the spatial domain. A mathematical model including the performance of the communication system as a function of the performance of the tracking system is derived. From this model we derive the optimum transmitter telescope gain. An example for a practical communication system between a low earth orbit satellite (LEO) and a geostationary earth orbit satellite (GEO) is presented. Using this model makes it possible to choose appropriate optics for the transmitter with reduced size and weight.

13 citations


Proceedings ArticleDOI
28 Oct 1996
TL;DR: In this article, the authors derived a mathematical model of a communication system that adapts optimally the transmitter beamwidth and the transmitted power to the tracking system performance, and investigated the performance of a communications system with discrete level optical phased array transmitter telescope gain.
Abstract: The basic free space optical communication system includes at least two satellites. In order to communicate between them, the transmitter satellite must track the beacon of the receiver satellite and point the information optical beam in its direction. Optical tracking and pointing systems for free space suffer during tracking from high amplitude vibration due to background radiation from interstellar objects such as sun, moon, earth and stars in the tracking field of view or mechanical impact from satellite internal and external sources. The vibrations of the beam pointing increase the bit error rate and jam communication between the two satellites. One way to overcome this problem is to increase the satellite receiver beacon power. However this solution requires increased power consumption and weight. These two factors are disadvantageous in satellite development. Considering these facts, we derive a mathematical model of a communication system that adapts optimally the transmitter beamwidth and the transmitted power to the tracking system performance. Based on this model, we investigate the performance of a communication system with discrete level optical phased array transmitter telescope gain. An example for a practical communication system between a low earth orbit satellite (LEO) and a geostationary earth orbit satellite (GEO) is presented. From the results of this work it is seen that a four level adaptive transmitter telescope is sufficient to compensate for vibration amplitude doubling. The benefits of the proposed model are less required transmitter power and improved communication system performance.

12 citations


Journal ArticleDOI
TL;DR: A new mathematical and optical engineering model for monitoring characteristics of aerosol clouds that includes the temporal transfer function of aerosols as a variable parameter in an electro-optic oscillator is presented.
Abstract: Monitoring, probing, and sensing characteristics of aerosol clouds is difficult and complicated. Probing the characteristics of aerosols is most useful in the chemical and microelectronic industry for processing control of aerosols and emulsion, decreasing bit error rate in adaptive optical communication systems, and in acquiring data for atmospheric science and environment quality. We present a new mathematical and optical engineering model for monitoring characteristics of aerosol clouds. The model includes the temporal transfer function of aerosol clouds as a variable parameter in an electro-optic oscillator. The frequency of the oscillator changes according to changes in the characteristics of the clouds (density, size distribution, physical thickness, the medium and the particulate refractive indices, and spatial distribution). It is possible to measure only one free characteristic at a given time. An example of a practical system for monitoring the density of aerosol clouds is given. The frequency of the oscillator changes from 1.25 to 0.43 MHz for changes in aerosol density from 2000 to 3000 particulates cm−3. The advantages of this new method compared with the transmissometer methods are (a) no necessity for line-of-sight measurement geometry, (b) accurate measurement of high optical thickness media is possible, (c) under certain conditions measurements can include characteristics of aerosol clouds related to light scatter that cannot be or are difficult to measure with a transmissometer, and (d) the cloud bandwidth for free space optical communication is directly measurable.

9 citations


Journal ArticleDOI
TL;DR: In this article, the extinction coefficients of aerosols are calculated using the PMS data, and those arising from molecular absorption are calculated by MODTRAN, and a simple and accurate model is obtained to predict dependence of the extinction coefficient on weather.
Abstract: Path-integrated atmospheric transmittance for visible wavelengths over a 5.5-km horizontal path is measured using black target contrast ratio. Measurements of on-line particulate distributions by particulate measuring system instrumentation (PMS) and of meteorological parameters are also performed. The extinction coefficients, primarily scattering, of aerosols are calculated using the PMS data, and those arising from molecular absorption are calculated by MODTRAN. Both extinction coefficients—the directly measured path-integrated ones and those calculated from particulate distribution and meteorological parameters near the receiver—are compared. Good agreement exists, especially when relative humidity is low, despite the fact that the second method involves aerosol size distribution by data collected from only a single point along the atmospheric path. Disagreement between both methods under high values of relative humidity can be explained by classification errors of the PMS instrumentation because of changes in the index of refraction of particles in a humid environment. Statistical regression analysis is made relating the measured transmittance values to online meteorological data. A simple and accurate model is obtained to predict dependence of the extinction coefficient on weather. The regression coefficients model shows that other meteorological parameters in addition to relative humidity are responsible for the changes in the atmospheric scattering coefficients. This contradicts the MODTRAN and Kasten-Hanel models for a continental atmosphere, which are based upon specific types of aerosols rather than a mixture of them.

9 citations


Proceedings ArticleDOI
05 Nov 1996
TL;DR: The method proposed here identifies the direction and the extent of the PSF of the blur and evaluates its shape which depends on the type of motion during the exposure, which permits fast high resolution restoration of the blurred image.
Abstract: A difficult problem in imaging systems is degradation of images caused by motion. In this paper we propose a method to identify important parameters with which to characterize the point spread function (PSF) of the blur, given only the blurred image itself. A first step of this method has been suggested in a former paper where only the blur extent parameter was considered. The identification method here is based on the concept that image characteristics along the direction of motion are different from the characteristics in other directions. The method proposed here identifies the direction and the extent of the PSF of the blur and evaluates its shape which depends on the type of motion during the exposure. Correct identification of the PSF parameters permits fast high resolution restoration of the blurred image.

9 citations


Proceedings ArticleDOI
22 Apr 1996
TL;DR: In this article, the authors derived a model of a communication system that adapts the communication system parameters to changes in received signal caused by changes in vibration amplitude, and compared the performance of the standard and adaptive models of communication systems for variable amplitudes of vibration amplitude.
Abstract: Satellites in free space suffer from periods of high displacement amplitude vibrations (for example: during the operation of the thruster, the antenna pointing mechanism, or the solar array drive mechanism). In order to utilize the advantages of optical communication in space, very narrow divergence transmitted beams are used. The high amplitude vibrations of the satellite cause decrease of received signal power in the receiver satellite due to mispointing of the transmitted beam. One way to overcome this problem is to develop very complicated stabilization systems. The disadvantages of this solution are: complexity, reliability, and cost. Most of the time, the amplitude of the vibrations is low and does not affect the communication performance. Considering these facts, we derive a model of a communication system that adapts the communication system parameters to changes in received signal caused by changes in vibration amplitude. The purpose of this model is to keep the bit error rate (BER) low and constant by adapting the system bandwidth and the receiver parameters to the vibration amplitude. The duration amplitude and occurrence of the high amplitude vibrations are assumed to be known so the adaptation of the communication system parameters is simple. The adaptive model is derived for the on off keying (OOK) modulation method. An example for practical optical space communication systems based on the adaptive model is given. Comparison and analysis of the performance of standard and adaptive models of communication systems for variable amplitudes of vibration amplitude are presented.

7 citations


Proceedings ArticleDOI
14 Oct 1996
TL;DR: In this paper, a Wiener filter is used to correct both turbulence and aerosol blur by enhancing the image spectrum at those high frequencies least affected by the jitter or randomness in turbulence MTF.
Abstract: Restoration for actual atmospherically blurred images is performed using a Wiener filter which corrects simultaneously for both turbulence and aerosol blur by enhancing the image spectrum primarily at those high frequencies least affected by the jitter or randomness in turbulence MTF. Correction is based upon predicted rather than measured atmospheric MTF. Both turbulence and aerosol MTFs are predicted using meteorological parameters measured with standard weather stations at the time and location where the image was recorded. A variety of weather conditions are considered. Past results have shown good correlation between measured and predicted atmospheric MTFs. Corrections are shown here for turbulence blur alone, for aerosol blur alone, and for both together. Since recorded images suffer frequently from poor contrast because of atmospheric path radiance, a simple image contrast improvement is also considered for the clarity of the atmospheric deblurring effect.

5 citations


Proceedings ArticleDOI
25 Oct 1996
TL;DR: In this paper, a new method of calculating the optical transfer function (OTF) for image blur caused by arbitrary motion is introduced, which makes it possible to obtain analytical expressions for OTF, deriving from any kind of motion, by means of the statistical moments of the motion function.
Abstract: A new method of calculating the optical transfer function (OTF) for image blur caused by arbitrary motion is introduced. Previous methods, except for a few specific types of motion, were numerical rather than analytical. This new method makes it possible to obtain analytical expressions for OTF, deriving from any kind of motion, by means of the statistical moments of the motion function. Analytical OTF expression are derived for high and low- frequency vibrations. An example of implementation of the method in restoration of images blurred by motion is presented.

2 citations


Proceedings ArticleDOI
05 Nov 1996
TL;DR: In this paper, the optical transfer function (OTF) was calculated for image blur caused by arbitrary motion and vibration by means of the statistical moments of the motion function, and an analytical OTF expression was derived for sinusoidal vibrations.
Abstract: A convenient form with which to quantify image degradation due to motion and vibration is the optical transfer function (OTF). We introduce a new method of calculating the OTF for image blur caused by arbitrary motion. Previous methods, except for a few specific types of motion, were numerical rather then analytical. This new method make it possible to obtain analytical expressions for the OTF, deriving from any kind of motion, by means of the statistical moments of the motion function. An analytical OTF expression is derived for sinusoidal vibrations. An example of the implementation of the method in restoration of images blurred randomly by low-frequency vibration is presented.

2 citations


Proceedings ArticleDOI
TL;DR: This paper considers the replacement of the use of a single detectable frequency to model the target acquisition process with one consisting of an integral of the target spectrum, taking into account the spatial frequency MTF dependence of the imaging system.
Abstract: Many of the standard considerations for modeling of target acquisition of stationary targets in a single field of view must be altered when considering target acquisition in the actual battlefield Sensors are scanning, targets are moving, and the detection process is considerably more complex than the analysis of the highest detectable frequency detectable superimposed on the target size In this paper, we discuss several of the issues involved The use of a single detectable frequency to model the target acquisition process is not sufficient We consider the replacement of this model with one consisting of an integral of the target spectrum, taking into account the spatial frequency MTF dependence of the imaging system

Proceedings ArticleDOI
14 Oct 1996
TL;DR: In this article, the influence of the position of the scattering layer along the optical axis on the image quality and modulation transfer function (MTF) is investigated, and the experimental results were compared to theoretical models based on the solution of the radiative transfer theory under the small angle approximation.
Abstract: Imaging quality of optical systems in a turbid environment is influenced not only by the contents of the turbid layer between the object and the optical receiver but also by the inhomogeneity of that medium. This is important particularly when imaging is performed through clouds, non homogeneous layers of dust, or over vertical or slant paths through the atmosphere. Forward small angle scattering influences more severely image quality and blur when the scattering layer is closer to the receiver. In this study the influence of the position of the scattering layer along the optical axis on the image quality and modulation transfer function (MTF) is investigated. The scattering layer was in controlled laboratory experiments consisted of calibrated polystyrene particles of known size and quantity. A point source was imaged by a computerized imaging system through a layer containing polystyrene particles and the point spread function (PSF) was recorded. The scattering MTF was calculated using the measured PSF. The MTF was measured as a function of the relative distance of the layer from the receiver. The experimental results were compared to theoretical models based on the solution of the radiative transfer theory under the small angle approximation.

Proceedings ArticleDOI
21 Oct 1996
TL;DR: In this paper, the atmospheric Wiener filter was used to correct for turbulence and aerosol blur and path radiance simultaneously in digital restoration of AVHRR imagery over the five wavelength bands of the satellite instrumentation.
Abstract: The recently developed atmospheric Wiener filter, which corrects for turbulence and aerosol blur and path radiance simultaneously, is implemented in digital restoration of AVHRR imagery over the five wavelength bands of the satellite instrumentation. Restoration is most impressive for higher optical depth situations, with improvement with regard to both smallness of size of resolvable detail and contrast Turbulence modulation transfer function (MTF) is calculated from meteorological data. Aerosol MTF is calculated from optical depth, measured with a sun-photometer. The product of the two yields atmospheric MiT which is implemented in the atmospheric Wiener filter. Image restorations with accompanying atmospheric MTF curves are presented. However, restoration results using a simple inverse MTF filter were quite similar. This indicates the satellite images were characterized by very low noise and that turbulence jitter was very limited which, in turn, indicates that the twbulencc MTFs integrated upwards over the path length were small compared to aerosol MTFs.

Proceedings ArticleDOI
21 Nov 1996
TL;DR: This research attempts to construct a reliable quantitative means of characterizing the perceptual difference between target and background by evaluating the extent to which it is possible to discriminate an object which has merged with its surroundings, in noise-limited and contrast limited images.
Abstract: Low noise images are contract-limited, and image restoration techniques can improve resolution significantly. However, as noise level increases, resolution improvements via image processing become more limited because image restoration increases noise. This research attempts to construct a reliable quantitative means of characterizing the perceptual difference between target and background. A method is suggested for evaluating the extent to which it is possible to discriminate an object which has merged with its surroundings, in noise-limited and contrast limited images, i.e., how hard it would be for an observer to recognize the object against various backgrounds as a function of noise level. The suggested model will be a first order model to begin with, using a regular bar-chart with additive uncorrelated Gaussian noise degraded by standard atmospheric blurring filters. The second phase will comprise a model dealing with higher-order images. This computational model relates the detectability or distinctness of the object to measurable parameters. It also must characterize human perceptual response, i.e. the model must develop metrics which are highly correlated to the ease or difficulty which the human observer experiences in discerning the target from its background. This requirement can be fulfilled only by conducting psychophysical experiments quantitatively comparing the perceptual evaluations of the observers with the results of the mathematical model.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.