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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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Proceedings ArticleDOI
TL;DR: In this article, the authors presented a comprehensive study of the Silicon Photomultiplier (SiPM) properties as a novel alternative for radiation detector light sensor and found that the SiPM low current consumption, its diminutive dimensions and the high gain make this technology of great interest for applications in portable radiation detection instrumentation based on scintillation material.
Abstract: This work presents a comprehensive study of the Silicon Photomultiplier (SiPM) properties as a novel alternative for radiation detector light sensor. The SiPM low current consumption, its diminutive dimensions and the high gain make this technology of great interest for applications in portable radiation detection instrumentation based on scintillation material. The development progress in investigation of the performance of the device incorporation with CsI(Tl) scintillation crystal during the R&D timeline is presented. The research shows the improvement in two major parameters: the noise level and the resolution. The finding emphasizes that the utilization of the SiPM as the light converting device in radiation sensors is potentially applicable for radiation detection and isotope identification.

2 citations

Proceedings ArticleDOI
01 Nov 2002
TL;DR: In this paper, the atmospheric Wiener filter is used to correct the effect of turbulence, aerosol blur, and path radiance on Landsat TM images. But, although aerosol MTF (modulation transfer function) is rather deterministic, turbulence MTF is random.
Abstract: Many properties of the atmosphere affect the quality of images propagating through it by blurring it and reducing its contrast, as well as blur. Use of the standard Wiener filter for correction of atmospheric blur is often not effective because, although aerosol MTF (modulation transfer function) is rather deterministic, turbulence MTF is random. The atmospheric Wiener filter is one method for overcoming turbulence jitter. The recently developed atmospheric Wiener filter, which corrects for turbulence blur, aerosol blur, and path radiance simultaneously, is implemented here in digital restoration of Landsat TM (thematic mapper) imagery over seven wavelength bands of the satellite instrumentation. Turbulence MTF is calculated from meteorological data or estimated if no meteorological data were measured. Aerosol MTF is consistent with optical depth. The product of the two yields atmospheric MTF, which is implemented in the atmospheric Wiener filter. Restoration improves both smallness of size of resolvable detail and contrast. Restorations are quite apparent even under clear weather conditions. Techniques for high resolution restoration involving more versatile filtering techniques, such as Kalman's and adaptive methods, are considered by filter comparison.

2 citations

Proceedings ArticleDOI
14 Apr 2000
TL;DR: In this paper, the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path is estimated and compared with beam widening caused by turbulence, and it is shown that the impact of atmospheric aerosols is significant.
Abstract: On a basis of a multiple-forward-scatter propagation model the atmospheric aerosol contributions to laser beam widening for a horizontal propagation path is estimated and compared with beam widening caused by turbulence. It is shown that the beam widening caused by atmospheric aerosols is significant, often even more significant than that caused by turbulence.

2 citations

Proceedings ArticleDOI
TL;DR: In this paper, the influence of Kolmogorov and non-Kolmoggorov turbulence statistics on laser communication links was analyzed for different propagation scenarios, and the effect of atmospheric turbulence on link performance was investigated.
Abstract: In free-space optical communication links, atmospheric turbulence causes fluctuations in both the intensity and the phase of the received light signal, affecting link performance. Influence of Kolmogorov and non-Kolmogorov turbulence statistics on laser communication links are analyzed for different propagation scenarios.

2 citations

Proceedings ArticleDOI
TL;DR: An analytical approach for estimating the vibration MTF from the measured system MTF by the frequency response of the sensor and their noise data based on point-spread function verification by the data of motion sensor characteristics.
Abstract: In this paper we investigate the influence of motion sensor errors on the derivation of the MTF and its implementation in image restoration. We present an analytical approach for estimating the vibration MTF from the measured system MTF by the frequency response of the sensor and their noise data. The goal of this research is to describe an automatic system of restoration of pictures blurred by vibration, and to consider its possible disadvantages. Our method is based on point-spread function verification by the data of motion sensor characteristics. We build an analytical model of the sensor and compare the MTF after sensor errors caused by noise of the system and wrong axis direction of the restoration device. Here, we assume that noise and signal are independent and noise of the system is white Gaussian noise. Some image restoration of degraded images is presented based on improvements of the original wiener filter. We compare performance of inverse and wiener filter operations and consider the dependence of restoration quality on the signal to noise ratio and angel between restoration axis and true vibration direction. There is an interesting and useful relationship in the final graphs. This article brings us to improvement of the initial method, as seen from our simulation. Some restorations of degraded images are presented based on improvements of the original wiener filter. The key to the restoration is determination of the improved optical transfer function unique to the image vibration and sensor characteristics.

1 citations


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Journal ArticleDOI

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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