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 …

I and i

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.

/pdf/a-parametric-texture-model-based-on-joint-statistics-of-2p5nbgtfy6.pdf

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

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.

/pdf/optical-coherence-tomography-principles-and-applications-17y32cabbm.pdf

Optical coherence tomography - principles and applications

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.

/pdf/survey-on-free-space-optical-communication-a-communication-239v68hfyw.pdf

Survey on Free Space Optical Communication: A Communication Theory Perspective

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.

/pdf/free-space-optical-communication-through-atmospheric-48mj86nu81.pdf

Free-space optical communication through atmospheric turbulence channels

A miniature neon indicator lamp, also known as a Glow Discharge Detector (GDD), costing about 50 cents, was found to be an excellent room temperature THz radiation detector. A proof of concept of 300 GHz heterodyne detection using GDD is demonstrated in this paper. Furthermore, a comparison to direct detection was carried-out and polarization effects on heterodyne detection were investigated. Preliminary results at 300 GHz showed better sensitivity by a factor of 20 with only 56 microwatt local oscillator power using heterodyne compared to direct detection. Further improvement of the detection sensitivity can be achieved if the Local Oscillator (LO) power (Plo) is increased. Effects of orthogonal polarizations of signal and local oscillator powers on heterodyne sensitivity were found to be surprisingly weak.

Heterodyne detection and polarization effects at 300 GHz using Ne indicator lamp glow discharge detectors

The classical method for determining target acquisition probabilities has always focused on the maximum spatial frequency (frmax) discernible in the image. On the other hand, it is known that the atmosphere degrades all the spatial frequencies as determined by the atmospheric modulation transfer function (MTF). The question arises: do the 'other' frequencies below frmax affect the target acquisition probability. We will present two experimental approaches to this question. In the first, we consider different atmospheric MTFs with the same value of frmax but with different MTF shapes. In the second, we consider a novel Wiener filter which restores all the frequencies to their value prior to the atmospheric blur. Laboratory measurements of observer response time when performing target acquisition will be presented for these case. The results will allow us to check the degree that the entire MTF should enter the target acquisition model, rather than frmax only.

Image restoration for target detection: will it help?

Remote sensing provides the ability for relatively rapid and early detection of the spatial distribution of a plant disease using methods based on thermography and canopy reflectance in visual and near-infrared wavebands. By remote mapping using color imaging and subsequent data analysis routines, it is possible to realize early detection, identification, and quantification of different relevant plant diseases. In the present work, an applicability of remote sensing with digital color imaging for detecting plant disease is demonstrated. The color and morphological features are used for analysis and classification purposes. As a case study, the image processing is applied to the color photos of banana fields obtained by a manned aerial vehicle equipped with a high resolution camera. Major banana diseases (e.g. panama etc.) exhibit symptoms on leaf area in their earlier stage of infection. Change of color and morphology features act as criteria used to identify and classify the disease. The results of plant disease recognition and identification are demonstrated.

Application of remote sensing for detecting plant disease using color and morphological features

Using atmospheric modulation transfer function area (MTFA) as a single-valued numerical criterion for image quality propagated through the atmosphere horizontally near the ground, a statistical study of atmospheric imaging data accumulated over a three year period has led to the determination of regression ceofficients with which to quantitatively predict image quality as a function of wavelength, over the 400 - 1000 nm wavelength region, according to weather forecast. 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 MTFA. The larger the expected MTFA, the better the expected image quality. Two sets of regression coefficient data have been obtained, one each for desert and non-desert climates, corresponding to summer and winter data here. Preliminary experimentation over a different line-of-sight indicates the accuracy of the prediction is fairly reliable for the summer or desert model.

Prediction Of Effects Of Weather On Image Quality Propagated Through The Atmosphere

Photodiode Quantum Efficiency Improvement through Vacuum Surface EffectsN. S. Kopeika, I. Hirsh and E. HazoutDept. Electrical and Computer EngineeringBen -Gurion University of the Negev, Beer -Sheva, Israel 84120AbstractSurface effects stemming simply from photodiode operation in vacuum environment are seen to improvequantum efficiency significantly. This is attributed to desorption of surface impurities and consequentreduction of surface potential, recombination, and Debye length. Effective depletion layer width can also benoticeably affected by free charge redistribution after desorption of surface impurities. Quantum efficiencyhere in vacuum is greatest at longer wavelengths because of decreased surface depth in vacuum.IntroductionAssuming all current carriers photo -generated in the junction depletion layer are collected, net photo-diode quantum efficiency n is limited by light reflectivity r of the device entrance face and the loss ofphotons absorbed between the front surface and the junction depletion layer. We call this d. Then, for adevice using a single pass of the incident light1 -3

Norman S. Kopeika

Papers

Heterodyne detection and polarization effects at 300 GHz using Ne indicator lamp glow discharge detectors

Image restoration for target detection: will it help?

Application of remote sensing for detecting plant disease using color and morphological features

Prediction Of Effects Of Weather On Image Quality Propagated Through The Atmosphere

Photodiode quantum efficiency improvement through vacuum surface effects