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Norman S. Kopeika

Bio: Norman S. Kopeika is an academic researcher from Ben-Gurion University of the Negev. The author has contributed to research in topics: Image restoration & Optical transfer function. The author has an hindex of 36, co-authored 371 publications receiving 5221 citations. Previous affiliations of Norman S. Kopeika include Ariel University & University of Pennsylvania.


Papers
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Journal ArticleDOI
01 Jul 1976
TL;DR: In this paper, a simple signal processing technique is demonstrated that can be used to recover a demodulated polarization modulation audio signal from the atmospheric modulation noise, which can then be used for the transmission of information over the atmospheric channel.
Abstract: Intesity modulation of optical signals by the atmosphere limits exploitation of the negligible atmospheric depolarization effects as a means of transmitting information over the atmospheric channel. A simple signal processing technique is demonstrated that can be used to recover a demodulated polarization modulation audio signal from the atmospheric modulation noise.

1 citations

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.

1 citations

Book ChapterDOI
09 Mar 1998
TL;DR: System design integrating the material from the previous eight chapters is emphasized strongly in the exercises and solutions and a more appropriate approach is stochastic rather than deterministic and is presented.
Abstract: In the previous two chapters the optical transfer function was introduced and its physical implications concerning contrast derived. In the present chapter, these results are applied toward determining image resolution in a quantitative manner. By resolution we mean the smallest size detail that can be resolved. This can be related to system optical transfer function and spatial frequency bandwidth. However, in reality image quality and resolution are very subjective parameters, varying considerably with each person’s visual system characteristics and its dependence on background irradiance—system signal-to-noise ratio. Therefore, the quantitative formulations presented in this and the next few chapters should be viewed as representative rather than as absolute quantities. A more appropriate approach is stochastic rather than deterministic and is presented as well. System design integrating the material from the previous eight chapters is emphasized strongly in the exercises and solutions.

1 citations

Proceedings ArticleDOI
23 Feb 1989
TL;DR: In this paper, the authors used the atmospheric modulation transfer function area (MTFA) as a single-valued numerical criterion for image quality propagated through the atmosphere and determined regression coefficients with which to quantitatively predict effects of windspeed, air temperature, and relative humidity on image quality.
Abstract: Using atmospheric modulation transfer function area (MTFA) as a single-valued numerical criterion for image quality propagated through the atmosphere, a statistical study of atmospheric imaging data has led to the determination of regression coefficients with which to quantitatively predict effects of windspeed, air temperature, and relative humidity on image quality propagated through the atmosphere as a function of wavelength over the 400-1000 nm wavelength region. Utilization of this procedure is quite simple. One simply plugs in expected values for windspeed, air temperature, and relative humidity in the regression coefficient expression for mcfa. The larger the expected mcfa, the better the expected image quality. Data for desert atmospheres have been presented previously. Here, the model for non-desert atmospheres is presented. Preliminary experimentation indicates the accuracy of the present model is quite good.

1 citations

Journal ArticleDOI
TL;DR: In this article, Si and Ge rectifier diodes are tested at frequent intervals of γ-radiation doses for changes in ideality factor η and minority carrier lifetime τ.
Abstract: Various Si and Ge rectifier diodes are tested at frequent intervals of γ‐radiation doses for changes in ideality factor η and minority carrier lifetime τ. Although both parameters are well known to decrease with dosage, here they are probably for the first time measured to also subsequently increase, decrease, increase, etc., at higher dosages. Examination of diodes in vacuum prior to and following even modest irradiation levels indicates experimentally that noticeable changes in surface properties have been induced by the irradiation. Such experimental techniques permit greater insight into the basic structure of surface phenomena long suspected to play a significant role in diode changes brought about by nuclear irradiation. Utilization of such surface changes leads to a broad general concept to explain the reversals and changes in the dosage dependences of η and τ in terms of bulk versus surface effects.

1 citations


Cited by
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Journal ArticleDOI

[...]

08 Dec 2001-BMJ
TL;DR: There is, I think, something ethereal about i —the square root of minus one, which seems an odd beast at that time—an intruder hovering on the edge of reality.
Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

33,785 citations

Journal ArticleDOI
TL;DR: A universal statistical model for texture images in the context of an overcomplete complex wavelet transform is presented, demonstrating the necessity of subgroups of the parameter set by showing examples of texture synthesis that fail when those parameters are removed from the set.
Abstract: We present a universal statistical model for texture images in the context of an overcomplete complex wavelet transform. The model is parameterized by a set of statistics computed on pairs of coefficients corresponding to basis functions at adjacent spatial locations, orientations, and scales. We develop an efficient algorithm for synthesizing random images subject to these constraints, by iteratively projecting onto the set of images satisfying each constraint, and we use this to test the perceptual validity of the model. In particular, we demonstrate the necessity of subgroups of the parameter set by showing examples of texture synthesis that fail when those parameters are removed from the set. We also demonstrate the power of our model by successfully synthesizing examples drawn from a diverse collection of artificial and natural textures.

1,978 citations

Journal ArticleDOI
TL;DR: OCT as discussed by the authors synthesises cross-sectional images from a series of laterally adjacent depth-scans, which can be used to assess tissue and cell function and morphology in situ.
Abstract: There have been three basic approaches to optical tomography since the early 1980s: diffraction tomography, diffuse optical tomography and optical coherence tomography (OCT). Optical techniques are of particular importance in the medical field, because these techniques promise to be safe and cheap and, in addition, offer a therapeutic potential. Advances in OCT technology have made it possible to apply OCT in a wide variety of applications but medical applications are still dominating. Specific advantages of OCT are its high depth and transversal resolution, the fact, that its depth resolution is decoupled from transverse resolution, high probing depth in scattering media, contact-free and non-invasive operation, and the possibility to create various function dependent image contrasting methods. This report presents the principles of OCT and the state of important OCT applications. OCT synthesises cross-sectional images from a series of laterally adjacent depth-scans. At present OCT is used in three different fields of optical imaging, in macroscopic imaging of structures which can be seen by the naked eye or using weak magnifications, in microscopic imaging using magnifications up to the classical limit of microscopic resolution and in endoscopic imaging, using low and medium magnification. First, OCT techniques, like the reflectometry technique and the dual beam technique were based on time-domain low coherence interferometry depth-scans. Later, Fourier-domain techniques have been developed and led to new imaging schemes. Recently developed parallel OCT schemes eliminate the need for lateral scanning and, therefore, dramatically increase the imaging rate. These schemes use CCD cameras and CMOS detector arrays as photodetectors. Video-rate three-dimensional OCT pictures have been obtained. Modifying interference microscopy techniques has led to high-resolution optical coherence microscopy that achieved sub-micrometre resolution. This report is concluded with a short presentation of important OCT applications. Ophthalmology is, due to the transparent ocular structures, still the main field of OCT application. The first commercial instrument too has been introduced for ophthalmic diagnostics (Carl Zeiss Meditec AG). Advances in using near-infrared light, however, opened the path for OCT imaging in strongly scattering tissues. Today, optical in vivo biopsy is one of the most challenging fields of OCT application. High resolution, high penetration depth, and its potential for functional imaging attribute to OCT an optical biopsy quality, which can be used to assess tissue and cell function and morphology in situ. OCT can already clarify the relevant architectural tissue morphology. For many diseases, however, including cancer in its early stages, higher resolution is necessary. New broad-bandwidth light sources, like photonic crystal fibres and superfluorescent fibre sources, and new contrasting techniques, give access to new sample properties and unmatched sensitivity and resolution.

1,914 citations

Journal ArticleDOI
TL;DR: An up-to-date survey on FSO communication systems is presented, describing FSO channel models and transmitter/receiver structures and details on information theoretical limits of FSO channels and algorithmic-level system design research activities to approach these limits are provided.
Abstract: Optical wireless communication (OWC) refers to transmission in unguided propagation media through the use of optical carriers, i.e., visible, infrared (IR), and ultraviolet (UV) bands. In this survey, we focus on outdoor terrestrial OWC links which operate in near IR band. These are widely referred to as free space optical (FSO) communication in the literature. FSO systems are used for high rate communication between two fixed points over distances up to several kilometers. In comparison to radio-frequency (RF) counterparts, FSO links have a very high optical bandwidth available, allowing much higher data rates. They are appealing for a wide range of applications such as metropolitan area network (MAN) extension, local area network (LAN)-to-LAN connectivity, fiber back-up, backhaul for wireless cellular networks, disaster recovery, high definition TV and medical image/video transmission, wireless video surveillance/monitoring, and quantum key distribution among others. Despite the major advantages of FSO technology and variety of its application areas, its widespread use has been hampered by its rather disappointing link reliability particularly in long ranges due to atmospheric turbulence-induced fading and sensitivity to weather conditions. In the last five years or so, there has been a surge of interest in FSO research to address these major technical challenges. Several innovative physical layer concepts, originally introduced in the context of RF systems, such as multiple-input multiple-output communication, cooperative diversity, and adaptive transmission have been recently explored for the design of next generation FSO systems. In this paper, we present an up-to-date survey on FSO communication systems. The first part describes FSO channel models and transmitter/receiver structures. In the second part, we provide details on information theoretical limits of FSO channels and algorithmic-level system design research activities to approach these limits. Specific topics include advances in modulation, channel coding, spatial/cooperative diversity techniques, adaptive transmission, and hybrid RF/FSO systems.

1,749 citations

Journal ArticleDOI
TL;DR: The use of ML detection in spatial diversity reception to reduce the diversity gain penalty caused by correlation between the fading at different receivers is described.
Abstract: In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, impairing link performance. We describe several communication techniques to mitigate turbulence-induced intensity fluctuations, i.e., signal fading. These techniques are applicable in the regime in which the receiver aperture is smaller than the correlation length of fading and the observation interval is shorter than the correlation time of fading. We assume that the receiver has no knowledge of the instantaneous fading state. When the receiver knows only the marginal statistics of the fading, a symbol-by-symbol ML detector can be used to improve detection performance. If the receiver has knowledge of the joint temporal statistics of the fading, maximum-likelihood sequence detection (MLSD) can be employed, yielding a further performance improvement, but at the cost of very high complexity. Spatial diversity reception with multiple receivers can also be used to overcome turbulence-induced fading. We describe the use of ML detection in spatial diversity reception to reduce the diversity gain penalty caused by correlation between the fading at different receivers.

1,490 citations