scispace - formally typeset
Search or ask a question
Author

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
More filters
Proceedings ArticleDOI
TL;DR: In this paper, a Middle East model of refractive turbulence strength (C n 2 ) vertical profile has been developed on the basis of a large set of imaging LIDAR measurements and the results of lidar measurements of aerosol size distribution, volume, and number concentration at different heights in the Mediterranean region (Be'er-Sheva, Israel) and comparison with models (AFGL, MODTRAN) are presented.
Abstract: The estimation of the performance of electro-optical systems depends on the accuracy of the atmospheric models being used in the propagation prediction codes. On the basis of a large set of imaging LIDAR measurements a Middle East model of refractive turbulence strength (C n 2 ) vertical profile has been developed. The model is presented in this work. Also, the results of lidar measurements of aerosol size distribution, volume, and number concentration at different heights in the Mediterranean region (Be'er-Sheva, Israel) and comparison with models (AFGL, MODTRAN) are presented. Implications can be important for optical communication, imaging through the atmosphere, and adaptive optics.

2 citations

Proceedings ArticleDOI
18 Oct 2004
TL;DR: In this paper, a model for predicting line-of-sight bending based on effects of turbulence and atmospheric conditions, described by pressure, temperature, relative humidity, etc, was developed and investigated.
Abstract: Line-of-sight bending, called "beam bending", is an effect caused by strong atmospheric turbulence, where during daytime targets are seen lower and during nighttime higher than their real locations This effect takes place in conditions of very low or absence of wind speed and relatively high turbulence, which characterize non-uniform atmospheres During past three years high-resolution experiments in different desert and low vegetation areas of the Middle East (Israel) were performed A model for predicting line-of-sight bending based on effects of turbulence and atmospheric conditions, described by pressure, temperature, relative humidity, etc, was developed and investigated This paper describes investigations made to parameterize this model based on high-percentage prediction of results for different areas, day/night time, and heights above the ground surface© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering Downloading of the abstract is permitted for personal use only

2 citations

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.

2 citations

Proceedings ArticleDOI
25 Oct 2016
TL;DR: In this article, a novel deterministic approach was used which is based on the remote sensing data to retrieve actual evapo-transpiration (ET) as a function of water availability can be measured remotely with infrared radiometers.
Abstract: The advancements in remote sensing in combination with sensor technology (both passive and active) enable growers to analyze an entire crop field as well as its local features. In particular, changes of actual evapo-transpiration (ET) as a function of water availability can be measured remotely with infrared radiometers. Detection of crop water stress and ET and combining it with the soil water flow model enable rational irrigation timing and application amounts. Nutrient deficiency, and in particular nitrogen deficiency, causes substantial crop losses. This deficiency needs to be identified immediately. A faster the detection and correction, a lesser the damage to the crop yield. In the present work, to retrieve ET a novel deterministic approach was used which is based on the remote sensing data. The algorithm can automatically provide timely valuable information on plant and soil water status, which can improve the management of irrigated crops. The solution is capable of bridging between Penman-Monteith ET model and Richards soil water flow model. This bridging can serve as a preliminary tool for expert irrigation system. To support decisions regarding fertilizers the greenness of plant canopies is assessed and quantified by using the spectral reflectance sensors and digital color imaging. Fertilization management can be provided on the basis of sampling and monitoring of crop nitrogen conditions using RS technique and translating measured N concentration in crop to kg/ha N application in the field.

2 citations

Proceedings ArticleDOI
22 Sep 1997
TL;DR: In this paper, the authors proposed a method to identify important parameters with which to characterize the point spread function (PSF) of the blur, given only the blurred image itself, based on the concept that image characteristics along the direction of motion are different than the characteristics in other directions.
Abstract: This paper deals with the problem of restoration of images blurred by relative motion between the camera and the object of interest. This problem is common when the imaging system is in moving vehicles or held by human hands, and in robot vision. For correct restoration of the degraded image we need to know the point spread function (PSF) of the blurring system. In this paper we propose a method to identify important parameters with which to characterize the PSF of the blur, given only the blurred image itself. The identification method here is based on the concept that image characteristics along the direction of motion are different than the characteristics in other directions. Depending on the PSF shape, the homogeneity and the smoothness of the blurred image in the motion direction are higher than in other directions. By filtering the blurred image we emphasize the PSF characteristics at the expense of the image characteristics. The method proposed here identifies the direction and the extent of the PSF of the blur and finally identifies the modulation transfer function (MTF) of the blurring system.

2 citations


Cited by
More filters
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