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.

Photoionization of excited atoms in dc gas discharges by low‐intensity light and its analogy to gas‐breakdown with high‐intensity lasers

Abstract: Spectral effects and nonlinearities that characterize illumination of dc discharges by low‐intensity light and illumination of gas cells by high‐intensity lasers are described. The similarities suggest an analogy between both cases. This analogy can be used to deepen the understanding of the low‐intensity EM radiation interaction with gas discharges and as a possible tool for further study of gas breakdown by high‐intensity lasers, including further investigation of the ’’effective photon’’ concept.

Atmospheric turbulence modulation transfer function for infrared target acquisition modeling

Abstract: A new direction for the US Army Night Vision and Electronic Sensors Directorate is the development of ultra-narrow field of view (UNFOV) infrared target acquisition (TA) systems. Frequently, the per- formance of these systems is limited by atmospheric turbulence in the imaging path. It is desirable to include the effects of atmospheric turbu- lence blur in infrared TA models. The current TA models are currently linear shift invariant (LSI) systems with component modulation transfer functions (MTFs). The use of additional MTFs, to account for atmo- spheric turbulence, requires that the turbulence blur have LSI properties. The primary unresolved issue with the treatment of turbulence blur as an MTF is the LSI characteristics of the blur. Significant variation in spatial blur and temporal blur prohibit the use of a single MTF in an LSI target acquisition model. Researchers at Ben-Gurion University (BGU) use a TA model that includes an LSI blur, which is a temporal average of the turbulence blur. The research described here evaluates the BGU-type treatment of atmospheric MTF and determines it reasonable for inclusion in the US Army's TA model. In addition to the spatial characteristics, the temporal variation of the turbulence blur is also described. © 2001 Society

Recognition of motion-blurred images by use of the method of moments.

Abstract: Image motion causes a blur that changes features of objects and therefore complicates the task of automatic recognition. In this work we develop two recognition methods for motion-blurred images. For the first method we assume that the motion function and direction during the exposure are given. We develop the relation between the blurred-image moments and the original-image moments based on the motion function only. The recognition is carried out by comparing the moments of the restored image against the moments of the image database. In the second method the motion function is not known. In this case image moments that are invariant with respect to the motion blur are identified, and only these moments are used for recognition. The advantage of the suggested methods is that no time-consuming image restoration is required prior to recognition.

Causes of atmospheric blur: comment on Atmospheric scattering effect on spatial resolution of imaging systems

Abstract: A paper by Ben Dor [J. Opt. Soc. Am. A14, 1329 (1997)] concludes that the blur we measured in our experiments was not atmospherically scattered light and that our theoretical model is incorrect because it violates the rules of linearity. Their work is based in part on “lack of raw data” in one of our experimental papers [J. Opt. Soc. Am A12, 970 (1995)]. We present here the raw data measured in the experiments in question, which show clearly the measured atmospherically scattered light. Similar raw data has also been published elsewhere regarding other experiments. We also clarify some rules of linear systems that justify our conceptual approach, which is shown to be similar to that of turbulence modulation transfer function. A review of several dozen experiments and analyses by other investigators all over the world that directly contradict the Ben Dor et al. results and conclusions is presented. The well-known significance of aerosol blur in imaging through the atmosphere from satellites is discussed, and pictorial examples of satellite imagery are shown for different atmospheric optical depths. It is noted that atmospheric point-spread-function analyses in the remote-sensing literature generally neglect turbulence blur altogether and deal with aerosol blur only, which is often called the adjacency effect, and that such phenomena are well supported by many different types of experiments and many different Monte Carlo simulations for many different aerosol and instrumentation parameter situations. The Monte Carlo simulation results of Ben Dor et al. are shown also to contradict everyday reality such as the solar aureole. This wealth of literature by others strongly contradicts the results of Ben Dor et al. and confirms our conclusion that forward scatter of light by aerosols is indeed a significant source of blur in imaging through the atmosphere, especially if atmospheric optical depth is on the order of unity or more. This can be confirmed, too, by any observer looking through binoculars at the moon and surrounding moonlight even on a clear night. A broad system engineering approach involving both aerosol and turbulence blur is called for.

Acquisition system for microsatellites laser communication in space

Abstract: Optical communications is a very complex task between satellites because of the small laser beam divergence and the large distance. Also, the vibrations of the satellites due to satellite internal systems and due to external sources may cause the laser beam to miss the intended satellite. In order to start the communication one of the satellites should start acquisition to compensate for possible large deviation angle between transmitter and receiver telescope lines of sight (LOS). During the communication if in the tracking process the satellite loses the connection the acquisition system should establish LOS quickly. In this paper are presented various acquisition search pattern methods such as raster and spiral, and different search methods such as scan/scan or scan/stare are analyzed. The influence of vibrations on these methods and compensation systems is discussed. Analysis of several components of the system is obtained through simulation.

I and i

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 …

A Parametric Texture Model Based on Joint Statistics of Complex Wavelet Coefficients

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.

Optical coherence tomography - principles and applications

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.

Survey on Free Space Optical Communication: A Communication Theory Perspective

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.

Free-space optical communication through atmospheric turbulence channels

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.