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.

Effects of image restoration on target acquisition

Abstract: In our work, we will focus on the atmospheric effects on the acquisition of a target and on image restoration by filtering the atmospheric effects such as: blur caused by absorption and scattering from aerosols and distortion caused by turbulence that changes the wave front angle, moves the image on the image plane, and blurs it. The restoration method using an atmospheric wiener filter is intended to correct the atmospheric effects. This filter is based on the fact that the modulation transmission function (MTF) of the turbulence is composed of a mean value and a random component while the aerosol MTF changes slowly. The project goal is the realization of the atmospheric wiener filter, finding the limitations (in terms of blur to noise ratio) of the filter through psycho-physical experiments and statistical analysis of the results. We found that the atmospheric wiener filter can improve target acquisition probability at low noise levels. As the noise increases the improvement becomes more limited because the restoration increases the noise level in the image.

How weather affects seeing through the atmosphere

Abstract: Calculations are made of regression coefficients in both the wavelength and spatial frequency domains for relative humidity, air temperature, and wind speed, with respect to atmospheric contrasts as measured over a three-year period. Significant changes are noted between summer and winter, including some sign changes and opposing wavelength dependences. Analysis of spatial frequency data permits determination of the effects of each meteorological parameter on background, turbulence, and aerosol modulation contrast functions separately. Results indicate that in the rainy season, when the atmosphere is freer of airborne soil-derived particulates, turbulence is dominant in limiting imaging resolution through the atmosphere, with wavelength dependence determined primarily by background and for ward scattering effects associated with humidity. Resolution is best in the near-infrared. However, in the dry season image quality is limited primarily by large airborne particulates and their effects on atmospheric background and spatial frequency dependent multiple forward scattering phenomena. In this case, resolution is best at short wavelengths. The strong wavelength dependences on small and large radii aerosol related effects suggest the possibility of predicting imaging resolution spectral dependence in advance in accordance with meteorological predictions. Analysis of regression coefficients in the spatial frequency domain permits quantitative determination of the effects of each meteorological parameter on each type of atmospheric MTF, i.e., background, aerosol, and turbulence MTFs, separately. In this way insight is gained not only as to the extent to which each meteorological parameter affects imaging resolution but also as to the basic mechanism of the effect.

Experimental comparison of three target acquisition models

Abstract: The role of the atmosphere in target acquisition modeling is investigated experimentally. Three models are compared to experimental results measured on the Golan Heights, israel. Concepts considered are atmospheric attenuation versus atmospheric blur, and contrast- limited (blur-limited) versus noise-limited imaging. Results indicate that the role of the atmosphere in target acquisition is blur rather than attenuation and that for ranges of the order of a few kilometers, modern sensors are limited by atmospheric blur rather than by noise. A significant portion of the atmospheric blur derives from small angle forward scattering by aerosols, which actually increases measured temperature differences for ranges up to a few kilometers.

Adaptive bandwidth for satellite optical communication

Abstract: Satellites in free space suffer from periods of high displacement amplitude vibrations. Most of the vibration is caused by satellite internal subsystems (such as thruster firing or solar array drive mechanism) and controlled by the satellite computer. To utilise the advantages of optical communication in space, very narrow divergence transmitted beams are used. The high-amplitude vibrations of the transmitter satellite cause a decrease in received signal power in the receiver satellite due to mispointing of the transmitted beam. In the paper, the authors 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. This model is useful for communication systems with two or more priorities of real time – for example, telephone calls and electronic mail. This means that, when the bandwidth shrinks, electronic mail messages may be delayed but the phone calls can continue. Comparison and analysis of the performance of practical standard and adaptive models of communication systems for variable vibration amplitude are presented.

Prediction of overall atmospheric MTF with standard weather parameters: comparison with measurements with two imaging systems

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

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.