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Showing papers by "Norman S. Kopeika published in 1995"


Journal ArticleDOI
TL;DR: In this paper, simultaneous and independent measurements of overall atmospheric modulation transfer function (MTF) and turbulence MTF over fairly long horizontal paths at 15m average elevation indicate that, even at midday, aerosol MTF deriving from forward scatter is usually more dominant than turbulence mTF.
Abstract: Although turbulence is usually considered to be the primary cause of image blur, simultaneous and independent measurements of overall atmospheric modulation transfer function (MTF) and turbulence MTF over fairly long horizontal paths at 15-m average elevation indicate that, even at midday, aerosol MTF deriving from forward scatter is usually more dominant than turbulence MTF. Three different experimental techniques are used, two passive and one active. Aerosol MTF measurements are accompanied by actual meteorological and coarse aerosol size distributions and scattering parameters at the times of MTF measurements. The wavelength dependence of aerosol and therefore of overall atmospheric MTF can be significant. This wavelength dependence and a usually well-defined knee can in no way be due to turbulence but can be explained by a significant aerosol MTF deriving from typical aerosol size distributions representative of other climates as well. Measurements confirm that the narrower the open-atmosphere aerosol scattering patterns and the greater the scattering densities, the greater the degradations of aerosol MTF and, consequently, of overall atmospheric MTF. Results imply that system design and image-restoration algorithms based on atmospheric turbulence only may often lead to image quality that is much poorer than if aerosol MTF is considered, too, with its proper proportional effect on imaging through the atmosphere. Whereas adaptive optics cannot correct for aerosol-derived blur, digital image restoration can.

47 citations


Journal ArticleDOI
TL;DR: In this article, the authors used meteorological dependences of both C2n (where Cn is the refractive index structure coefficient) and the coarse aerosol size distribution to predict the turbulence MTF, aerosol MTF and overall atmospheric modulation transfer function according to the weather.
Abstract: The overall atmospheric modulation transfer function (MTF) is essentially the product of the turbulence and aerosol MTFs. Models describing meteorological dependences of both C2n (where Cn is the refractive index structure coefficient) and the coarse aerosol size distribution have been developed previously. Here, they are used to predict the turbulence MTF, aerosol MTF, and overall atmospheric MTF according to the weather. Comparison of predictions with measurements yields very low mean squared normalized error and suggests that such prediction models can also be very useful in image restoration based on weather data at the time and general location in which the image was recorded. An interesting aspect of this work is that measurements of the aerosol MTF with different imaging instrumentation are very different, as expected from theory developed previously concerning the practical aerosol MTF actually recorded in the image. This is dependent on instrumentation parameters. This experimental verification with two different imaging systems supports the model that the "practical" aerosol MTF is very dependent on instrumentation.

26 citations


Journal ArticleDOI
TL;DR: In this article, the average atmospheric modulation transfer function (MTF) at the time the image is received is used to help overcome the jitter characteristics of turbulence, and is capable of yielding real-time image restoration with resolution limited essentially only by the hardware itself.
Abstract: A new method of real-time high-resolution imaging through the atmosphere is presented. This technique is based on knowledge of average atmospheric modulation transfer function (MTF) at the time the image is received. Atmospheric effects are modeled by a noisy spatial frequency filter including an average component described by the average atmospheric MTF and a noisy component modeled by the atmospheric point spread function's power spectral density. The noisy component represents random changes in the atmospheric MTF. Analytical results are accompanied by experimental image restoration examples, indicating significant image quality improvement based on knowledge of average atmospheric MTF, which includes both turbulence and aerosol MTF components. This method can be used to help overcome the jitter characteristics of turbulence, and is capable of yielding real-time image restoration with resolution limited essentially only by the hardware itself. Turbulence blur, aerosol blur, and contrast degradation are all corrected simultaneously, unlike adaptive optics, which corrects for turbulence only.

24 citations


Journal ArticleDOI
TL;DR: In this paper, Johnson et al. considered the incorporation of atmospheric aerosol and turbulence effects into visible, near-infrared, and thermal infrared target acquisition modeling and showed how the target acquisition probabilities and, conversely, the ranges at which objects can be detected are changed by the inclusion of atmospheric effects.
Abstract: The incorporation of atmospheric aerosol and turbulence effects into visible, near-infrared, and thermalinfrared target acquisition modeling is considered. We show how the target acquisition probabilities and, conversely, the ranges at which objects can be detected are changed by the inclusion of atmospheric effects. It is assumed that images are contrast limited rather than noise limited, as is indeed the case with most visible, near-infrared, and thermal infrared sensors. For short focal lengths with low angular magnification, atmospheric effects on target acquisition are negligible. However, for longer focal lengths with large angular magnification, resolution is limited by the atmosphere, and this has a strong adverse effect on target acquisition probabilities, times, and ranges. The considerable improvement possible with image correction for atmospheric blur automatically in a fraction of a second is significant for contrast-limited imaging and is also discussed. Knowledge of the atmospheric modulation transfer function is essential to good system design and is also useful in image restoration for any type of target or object. Finally, a new target-transferfunction model is suggested that considers the overall image-spectrum target received by the human visual system rather than only the main harmonic detail as in the Johnson chart model. [ J. Johnson , in Proceedings of Seminar on Direct-Viewing Electro-Optical Aids to Night Vision ( IDA, Alexandria, Va., 1966), p. 177.]

24 citations


Journal ArticleDOI
TL;DR: In this article, the authors consider the effects of instrumentation and conclude that aerosol modulation transfer function (MTF) in the image plane is insignificant, whereas the values of maximum angles for scattered and unscattered (θ 0) light used in the Comment refer to the optics plane.
Abstract: New exact numerical calculations as well as exact calculations in J. Opt. Soc. Am. A10, 172 ( 1993) indicate that the approximations in the Comment in J. Opt. Soc. Am. A11, 1175 ( 1994) are based on faulty perceptions of basic scattering phenomena and on a misreading of our paper. The Comment does not sufficiently consider effects of instrumentation. Whereas our model refers to the aerosol modulation transfer function (MTF) in the image plane, the values of maximum angles for scattered (θS) and unscattered (θ0) light used in the Comment refer to the optics plane. The Comment does not consider the fact that dynamic range limits (θS) in the image, whereas limited spatial-frequency bandwidth broadens θ0 in the image, each by orders of magnitude. Therefore the Comment’s conclusion contradicts experimental results obtained by numerous researchers. The Comment’s conclusion that aerosol MTF is insignificant is based on that author’s own experiments, in which clear weather and haze atmospheric MTF (composed of turbulence and aerosol MTF’s) could not be measured, the reason being insufficient equipment resolution, rather than insignificant turbulence or aerosol MTF. Furthermore, the claim in our original paper that aerosol MTF is extremely significant has since been supported by many different types of experiments that included short and long exposures, thermal imaging, and image restoration based on atmospheric MTF, including a highly significant practical, uniquely shaped, aerosol MTF.

19 citations


Patent
06 Jun 1995
TL;DR: In this paper, a real-time high resolution imaging through the atmosphere is presented based on knowledge of average atmospheric Modulation Transfer Function (MTF) at the time the image is received.
Abstract: A method of real-time high resolution imaging through the atmosphere is presented. This technique is based on knowledge of average atmospheric Modulation Transfer Function (MTF) at the time the image is received. Atmospheric effects are characterized by a noise spatial frequency filter including an average component described by the average atmospheric Modulation Transfer Function, and a noisy component modeled by the atmospheric Point Spread Function's power spectral density. The noisy component represents random changes in atmospheric MTF. The new method of image restoration results in significant image quality improvement based upon knowledge of average atmospheric MTF which includes both turbulence and aerosol MTF components. This method can be used to help overcome the jitter characteristics of turbulence, and is capable of yielding real-time image restoration with resolution limited essentially only by the hardware itself. Turbulence blur, aerosol blur, and contrast degradation are all corrected simultaneously in real time.

19 citations


Journal ArticleDOI
TL;DR: In this paper, a mathematical model of spatial widening of the optical beam is derived using Monte Carlo simulation at three different wavelengths in the visible and the near IR, and it is shown that using shorter wavelengths such as 0532 μm results in least spatial widening and maximal received power, and is thus preferable for optical communication.
Abstract: As part of a communication channel, clouds cause spatial widening and attenuation of optical pulse power Free-space optical communication from satellite to earth (ground or airplane) occasionally involves clouds over part of the optical channel Most of the energy of optical pulses propagating through thin clouds passes through the clouds The propagating energy is concentrated around the center of the beam The distribution of the energy relative to the center of the beam is not uniform Using the received energy in an efficient way reduces the transmitter power needed for given bit error rate The advantages of low transmitter power are less radiation exposure and greater immunity to eavesdropping To use the received energy efficiently, a mathematical model of spatial widening of the optical beam is derived using Monte Carlo simulation The simulation is carried out at three different wavelengths in the visible and the near IR Important aspects of this work include the fact that (1) using shorter wavelengths such as 0532 μm results in least spatial widening and maximal received power, and is thus preferable for optical communication, and (2) the mathematical model derived is a basis for adaptive communication with less transmitted energy consumption

16 citations


Journal ArticleDOI
TL;DR: In this article, the restoration of thermal images distorted by the atmosphere, detected with a focal plane array (FPA) Pt-Si thermal imaging system, is presented based upon atmospheric modulation transfer function (MTF) analysis.

12 citations


Journal ArticleDOI
TL;DR: In this article, a mathematical model for optimum performance of digital optical communication through clouds is developed based on mathematical models of spatial widening of optical radiation derived by Monte Carlo simulation, the purpose of the optimum adaptive communication system suggested here is to improve the bit error rate (BER) by optimizing according to meterological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable.
Abstract: Optical communication must contain clouds as parts of communication channels. Propagation of optical pulses through clouds causes widening in the spatial domain and attenuation of the pulse radiant power. These effects decrease the received signal and increase bit error rate (BER). One way to improve the BER of the communication system is by using adaptive methods to obtain more signal relative to noise power. Based on mathematical models of spatial widening of optical radiation derived by Monte Carlo simulation, a mathematical model for optimum performance of digital optical communication through clouds is developed. The purpose of the optimum adaptive communication system suggested here is to improve the BER by optimizing according to meterological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable. Comparison and analysis of three models of communication systems in fog cloud channels are presented: (1) the optimum adaptive detector array aperture, (2) an ordinary single detector aperture of the same size, and (3) a small detector aperture. Improvement of more than four orders of magnitude in BER under certain conditions is possible with the new adaptive system model.

12 citations


Proceedings ArticleDOI
15 Jun 1995
TL;DR: In this paper, a mathematical model for optimum performance of digital optical communication through clouds is developed based on mathematical models of spatial widening of optical radiation derived by Monte-Carlo simulation, and the purpose of the optimum adaptive communication system suggested here is to improve the bit error rate by optimizing according to meteorological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable.
Abstract: Optical communication must contain clouds as parts of communication channels. Propagation of optical pulses through clouds causes widening in the spatial domain and attenuation of the pulse radiant power. These effects decrease the received signal and increase bit error rate (BER). One way to improve the BER of the communication system is by using adaptive methods to obtain more signal relative to noise power. Based on mathematical models of spatial widening of optical radiation derived by Monte-Carlo simulation, a mathematical model for optimum performance of digital optical communication through clouds is developed. The purpose of the optimum adaptive communication system suggested here is to improve the BER by optimizing according to meteorological conditions the spatial distribution of the detected radiation beam using a detector array where the external amplification of each detector is adaptable. Comparison and analysis of three models of communication systems in fog cloud channels are presented: (1) the optimum adaptive detector array aperture, (2) an ordinary single detector aperture of the same size, and (3) a small detector aperture. Improvement of more than four orders of magnitude in bit error rate under certain conditions is possible with the new adaptive system model.

12 citations


Proceedings ArticleDOI
15 Jun 1995
TL;DR: In this article, the authors used meteorological dependences of both Cn2 and coarse aerosol size distribution to predict turbulence, aerosol MTF, and overall atmospheric MTF according to weather.
Abstract: Overall atmospheric modulation transfer function (MiT) is essentially the product of turbulence and aerosol MTF. Models describing meteorological dependences of both Cn2 and coarse aerosol size distribution have been developedpreviously. Here, they are used to predict turbulence MiT, aerosol MTF, and overall atmospheric MTF according to weather. Comparison of predictions to measurements yields very high correlations and suggests that such prediction modelscan also be very useful in image restoration based on weather data at the time and general location in which the image wasrecorded. An interesting aspect of this work is that measurements of aerosol MTF with different imaging instrumentationare very different, as expected from theory developed previously concerning the practical aerosol MTF actually recorded inthe image. This is dependent upon instrumentation parameters. This experimental verification supports the model that the"practical" aerosol MiT is very dependent upon instrumentation.Key words: atmospheric optics, aerosols, aerosol MiT, turbulence, weather, image restoration

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the effect of atmospheric modulation transfer function (MTF) spatial frequency dependence on the target acquisition probability and the range at which targets can be detected.

Proceedings ArticleDOI
26 May 1995
TL;DR: In this article, the authors derived the optical transfer function (OTF) from the relative displacement between the camera and the object using a motion sensor, and fitted it to a sinusoidal function.
Abstract: This paper deals with the restoration of images blurred as a result of image motion or vibration The key for restoration algorithm success is to derive accurately the Optical Transfer Function (OTF) representing the image motion degradation in the spatial frequency domain The basic method of obtaining the OTF from the relative displacement between the camera and the object using a motion sensor has been developed recently and is discussed elsewhere In this paper, the motion function is derived instead from analysis of a sequence of images The first step is to obtain the image motion information from the sequence of images according to two well known algorithms - the Block Matching Algorithm (BMA) and Edge Trace Tracking (ETT) The basis for these two methods consists of tracking a block or an edge through a sequence of several images The results of these two methods were fitted to a sinusoidal function, compared, and there was excellent agreement between them Finally, the image is restored using the OTF obtained from the tracking method

Journal ArticleDOI
TL;DR: The methods presented here are capable of yielding real-time image restoration with the resolution essentially limited by only the hardware in both wavelength regions, with no one technique the most advantageous.
Abstract: A system approach is applied to overcome atmospheric degradation of remotely sensed images. A comparison is presented between different filtering techniques for restoration of distorted images for both the visible and thermal IR spectral regions. Restoration methods include spatial and spatial frequency filters. Best results are obtained by using a fractal model to describe the image's power spectral density for scenes in the visible spectral range. Atmospheric effects are best modeled by a noisy spatial frequency filter composed of an average component described by the average atmospheric and hardware modulation transfer function and a noisy component modeled by the atmospheric point spread function's power spectral density. The most impressive restorations in the visible range are achieved by combining the last model and the fractal model for the object's power spectral density. In the thermal range, however, several restoration techniques yielded very good results, with no one technique the most advantageous. The methods presented here are capable of yielding real-time image restoration with the resolution essentially limited by only the hardware in both wavelength regions.

Journal ArticleDOI
TL;DR: This research analyzes the influence of image vibrations and motion on the probability of acquiring a target with an ATR system and includes accepted metrics that characterize the relationship existing between the target and its background.
Abstract: The resolution capability of imaging systems is affected by blur resulting from vibration and motion during the exposure. This blur is often more severe than electronic and optical resolution limitations inherent in the system. Such image quality degradation must be considered when dealing with the development and analysis of automatic target recognition (ATR) systems. This research analyzes the influence of image vibrations and motion on the probability of acquiring a target with an ATR system. The analysis includes accepted metrics that characterize the relationship existing between the target and its background. A high level of correlation is expected between these factors and the probability of target detection permitting efficient performance in the prediction and evaluation of any ATR system. Such correlations are considered here in the presence of sensor motion and vibration and situations are considered in which the probability of recognition is improved by the motion, despite the blur. The results of this research can be implemented in military applications as well as in developing image restoration procedures for image-blur conditions.

Proceedings ArticleDOI
22 May 1995
TL;DR: A new method for identification of the blur extent in an image, blurred by motion of the camera during the exposure time, is presented and is based on a concept that there exists a correlation between the pixels along the blur of the original unblurred pixels.
Abstract: In imaging systems in moving vehicles such as tanks, planes, ships, rpvs, etc., resolution is usually limited by motion blur. Successful restoration of blurred images depends primarily on the knowledge we have about the degradation process parameters, i.e., the point spread function (PSF) of the blur and the noise statistics. For many blur situations, such as those deriving from uniform or sinusoidal motion, the most important parameter for proper identification of the PSF is the blur extent parameter. This parameter is the smear size in the blurred image of a point object in the original image. A new method for identification of the blur extent in an image, blurred by motion of the camera during the exposure time, is presented in this paper. The blur extent identification is determined from the motion-blurred and noisy image itself. The identification method developed here is based on a concept that there exists a correlation between the pixels along the blur of the original unblurred pixels. In order to expose the hidden information about the blur extent, the blurred image is first transformed to a secondary image that is more informative about the blur extent, and then the blur extent is extracted from this image using correlation attributes in the image. This permits fast high resolution restoration when the blur extent can complete our knowledge about the blur properties.

Journal ArticleDOI
TL;DR: In this paper, an effort to quantify effects of weather in the northern Negev desert on airborne particle concentration and on cross-sectional area per unit volume, so as to permit prediction according to weather, has begun.
Abstract: An effort to quantify effects of weather in the northern Negev desert on airborne particle concentration and on cross-sectional area per unit volume, so as to permit prediction according to weather, has begun. Correlations of prediction with measurement are on the order of 94% and 91%, respectively. Humidity is the dominant weather parameter, as expected, but it is not the only parameter. There is statistical significance too to solar flux, air temperature, and wind speed. The empirical model here provides a means of comparing theoretical models of effects of weather on airborne particle statistics with real-world phenomena. It is suggested that these models may well be applicable elsewhere, since the newly airborne particles are only a small fraction of the total airborne amount.

Journal ArticleDOI
TL;DR: In this article, the effects of low frequency mechanical vibrations on thermal imaging target acquisition are considered and a model is described that takes as input mechanical vibration data such as amplitude and frequency as well as the physical characteristics of the target.

Proceedings ArticleDOI
02 Jun 1995
TL;DR: In this paper, the incorporation of atmospheric aerosol and turbulence blur and motion blur into visible, near infrared, and thermal infrared target acquisition modeling is considered, and the authors show how the target acquisition probabilities and, conversely, the ranges at which objects can be detected are changed by the inclusion of these real-life environmental effects whose blur is often significantly greater than that of imaging system hardware.
Abstract: In this paper, the incorporation of atmospheric aerosol and turbulence blur and motion blur into visible, near infrared, and thermal infrared target acquisition modeling is considered. Here, we show how the target acquisition probabilities and, conversely, the ranges at which objects can be detected are changed by the inclusion of these real-life environmental effects whose blur is often significantly greater than that of imaging system hardware. It is assumed that images are contrast-limited rather than noise-limited, as is indeed the case with most visible, near infrared (IR), and thermal IR sensors. For short focal lengths with low angular magnification, such environmental blur effects on target acquisition are negligible. However, for longer focal lengths with large angular magnification, resolution is limited by them and this has a strong adverse effect on target acquisition probabilities, times, and ranges. The considerable improvement possible with image correction for such environmental blur automatically in a fraction of a second is significant for contrast-limited imaging, and is discussed here too. Knowledge of such environmental MTF is essential to good system design and is also very useful in image restoration for any type of target or object.

Proceedings ArticleDOI
22 Aug 1995
TL;DR: This research suggested and developed a method for calculating numerically the optical transfer function (OTF) for any type of image motion and uses different algorithms for the reconstruction of an image, according to the OTF of the lung motion, which is in several directions simultaneously.
Abstract: When carrying out medical imaging based on detection of isotopic radiation levels of internal organs such as lungs or heart, distortions and blur arise as a result of the organ motion during breathing and blood supply. Consequently, the image quality declines, despite the use of expensive high resolution devices. Hence, such devices are not exploited fully. There is a need to overcome the problem in alternative ways. Such as alternative is image restoration. We suggested and developed a method for calculating numerically the optical transfer function (OTF) for any type of image motion. The purpose of this reserach is restoration of original isotope images (of the lungs) by reconstruction methods that depend on the OTF of the real time relative motion between the object and the imaging system. This research uses different algorithms for the reconstruction of an image, according to the OTF of the lung motion, which is in several directions simultaneously. One way of handling the 3D movement is to decompose the image into several portions, to restore each portion according to its motion characteristics, and then to combine all the image portions back into a single image. As additional complication is that the image was recorded at different angles. The application of this reserach is in medical systems requiring high resolution imaging. The main advantage of this approach is its low cost versus conventional approaches.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Journal ArticleDOI
TL;DR: The search strategy in field-of-regard infrared target acquisition, including random, ‘windshield-wiper’ and ‘typewriter’, is considered and the results are used to predict the performance of actual military systems.

Proceedings ArticleDOI
17 Apr 1995
TL;DR: In this article, the size distribution parameters measured by optical counters are related to weather parameters, which can be used to predict under which conditions the MODTRAN aerosol models have good or poor accuracy.
Abstract: Predictions of atmospheric transmittance in desert aerosol environments using MODTRAN code diverge significantly from measured data. Good prediction of the desert particulate size distribution is required in order to predict atmospheric scattering and absorption parameters. It is also essential to the prediction of the aerosol atmospheric modulation transfer function which is often the dominant component of the overall atmospheric MTF. Recently, an effort to predict statistics but not size distribution according to simple weather parameters has been made for coarse desert aerosols. A quantitative analysis of the desert particulate size distribution models was also performed. In this research the size distribution parameters measured by optical counters are related to weather parameters. Known statistical and analytical models such as MODTRAN relate the size distribution parameters only to relative humidity for continental atmospheres. Although humidity has a significant role in the prediction of aerosol size statistics, other weather parameters are seen here to strongly influence also the size distribution parameters. Comparisons such as the above can be used to predict under which conditions the MODTRAN aerosol models have good or poor accuracy. It is also hoped that they will lead to improvements in MODTRAN, improving the accuracy of the humidity dependence as well as by incorporating other meteorological parameters into the MODTRAN prediction models.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
07 Mar 1995
TL;DR: A new method for identification of the blur extent in an image, blurred by horizontal motion of the camera during the exposure time, is presented and is based on the error characteristics due to the intentional use of inappropriate PSFs in the restoration process.
Abstract: Successful restoration of blurred images depends primarily on the knowledge we have about the degradation process parameters, i.e., the point spread function (PSF) of the blur and the noise statistics. In many blur types, such as uniform or sinusoidal motions, the most important parameter for proper identification of the PSF is the blur extent parameter. This parameter is the smear size in the blurred image of a point object in the original image. A new method for identification of the blur extent in an image, blurred by horizontal motion of the camera during the exposure time, is presented in this paper. The blur extent identification is accomplished given only the motion-blurred and noisy image. The identification approach here is based on the error characteristics due to the intentional use of inappropriate PSFs in the restoration process. The knowledge of the camera displacement permits high resolution image restoration when this parameter can relate to a specific PSF such as that characterizing linear motion or vibrations. Since the approach is not iterative the computing time is relatively short.

Journal ArticleDOI
TL;DR: In this paper, a correction to the definition of the atmospheric coherence diameter is suggested, based on the existence of a practical instrumentation-based aerosol modulation transfer function (MTF), which is often the dominant ingredient of atmospheric MTF.
Abstract: A correction to the definition of the atmospheric coherence diameter is suggested here, based on the existence of a practical instrumentation-based aerosol modulation transfer function (MTF), which is often the dominant ingredient of the atmospheric MTF. As defined classically by Fried about 25 yr ago, atmospheric MTF and coherence diameter were related to turbulence MTF only. Lutomirski considered diftractive aerosols, too, but did not consider effects of instrumentation on scattering angles actually recorded in the image. These are limited in the real world by instrumentation to milliradians, rather than by the broad angular spread of diffraction to radians. In the case of a Gaussian approximation of the practical aerosol MTF, an analytical expression is derived for the practical aerosol-derived coherence diameter. This parameter is related to the practical aerosol MTF's cutoff frequency, and to its asymptotic value at high spatial frequencies. Thus, a more general concept of atmospheric coherence diameter is proposed here, which is relevant to actual real-world imaging systems, whether they are passive or active. Quantitative validation of the theory is presented, based on both simulations and actually measured atmospheric MTFs in both the visible and thermal infrared spectral ranges. Overall atmospheric coherence diameter is determined generally by the smaller of the turbulence and practical aerosol coherence diameters, depending on optical depth. The results here appear applicable particularly to cost-effective thermal imaging system design, although applications are considered, too, for the visible and near infrared. For example, blur deriving from aerosol scatter should have much less effect in coherent detection laser radar (LIDAR) than in direct detection imaging.

Proceedings ArticleDOI
07 Mar 1995
TL;DR: In this paper, the optical transfer function appropriate to any type of image motion and vibration, including random ones, has been developed, and the close agreement justifies implementation in image restoration for blurring deriving from any typeof image motion.
Abstract: A method of calculating numerically the optical transfer function appropriate to any type of image motion and vibration, including random ones, has been developed. This method has been verified experimentally, and the close agreement justifies implementation in image restoration for blurring deriving from any type of image motion. The goal of this research is to recover the original image from its degraded version. There are many methods of image restoration based on the point spread function. One of the common methods is the Wiener filter. Here, some image restorations of physically degraded images are presented, based on a constrained least squares improvement of the original Wiener filter. The key to restoration is determination of the optical transfer function unique to each particular image motion and vibration.

Proceedings ArticleDOI
06 Jun 1995
TL;DR: In this article, a model for reliability of digital optical communication in a particulate scattering environment is presented, and an adaptive method to improve and in some cases to make possible communication is suggested.
Abstract: Decrease in signal to noise ratio and maximum bit rate, as well as increase in error probability in optical digital communication are caused by particulate light scatter in the atmosphere and in space. Two effects on propagation of laser pulses are described: (1) spatial widening of transmitted beam and (2) attenuation of pulse radiant power. Based on these results a model for reliability of digital optical communication in a particulate scattering environment is presented. Examples for practical communication systems are given. An adaptive method to improve and in some cases to make possible communication is suggested. Comparison and analysis of two models of communication systems for the particulate scattering channel are presented: (1) transmitter with high bit rate and receiver with avalanche photodiode and (2) transmitter with variable bit rate and a new model for an adaptive circuit in the receiver. An improvement of more than seven orders of magnitude in error probability under certain conditions is possible with the new adaptive system model.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Proceedings ArticleDOI
06 Jun 1995
TL;DR: In this paper, a method is derived to determine the probability of detection for targets which have been blurred by sensor motion, which is then applied to restored and non-corrected pictures.
Abstract: Image blurring due to sensor motion can often be the limiting factor in the resolution of the picture and, hence, on our ability to detect targets. In a recent paper, we've proposed a method for the restoration of such images; good results have been obtained. In this paper we propose to quantitatively evaluate the effect of such a restoration process on automatic target acquisition. A method is derived to determine the probability of detection for targets which have been blurred by sensor motion. This method is then applied to restored and non-corrected pictures. The degree to which such real-time restoration is worthwhile is discussed.

Proceedings ArticleDOI
06 Jun 1995
TL;DR: In this article, the authors incorporated atmospheric aerosol and turbulence effects into visible and infrared search modeling and showed how the target acquisition probabilities and, conversely, the ranges at which targets can be detected are changed by the inclusion of atmospheric effects.
Abstract: In this paper incorporation of atmospheric aerosol and turbulence effects into visible and infrared search modeling is considered. Here, we show how the target acquisition probabilities and, conversely, the ranges at which targets can be detected are changed by the inclusion of atmospheric effects. It is assumed that images are contrast-limited rather than noise-limited, as is indeed the case with most visible, near infrared (IR) and thermal IR sensors of high quantum efficiency. For short focal lengths with low angular magnification, atmospheric effects on target acquisition are negligible. However, for longer focal lengths with large angular magnification, resolution is limited by the atmosphere and this has a strong adverse effect on target acquisition probabilities, times, and ranges. The considerable improvement possible with image correction for atmospheric blur automatically in real time is significant for contrast-limited imaging, and is discussed here too. Knowledge of atmospheric MTF is essential to good system design. It is also very useful in image restoration for any type of target or object.