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We present the first results of a custom low-noise silicon photodiode detector designed for use with X-ray capillary optics. This system is intended to perform as a smaller, lighter, and low-powered alternative to currently existing X-ray telescope technologies. The detector has an active area with a diameter of 100 $\mu \text{m}$ , and its small size leads to a low capacitance of well under 1 pF and a leakage current of 1 pA or less at the depletion voltage. We tested the detector with both a discrete preamp and an ultralow-noise front-end application-specific integrated circuit (ASIC). The front-end ASIC, developed at Brookhaven National Laboratory, was designed for low-capacitance detectors but had not been previously tested with a detector. Here, we discuss the detector design, the experimental setup, and the resulting detector performance. Using radioactive laboratory sources, we measure a full-width at half-maximum (FWHM) of 211 ± 8 eV at 5.9 keV with the ASIC and are able to set the threshold as low as 0.6 keV. [ABSTRACT FROM AUTHOR]

This work is to investigate the instrumentation implementing issues of back focal plane (BFP)-typed apertometer. Firstly, we introduce a general instrument architecture of the BFP-typed apertometer, including the hardware (optics and mechanics) of the system, operation procedures of control and measurement system, and also the digital image processing algorithm/software. Secondly, we are the first to discuss the gradual rising effect of total-internal-reflection (TIR) phenomenon, the criteria on how to “exactly” locate the reference ring on BFP images, and the corresponding accuracies. As a significantly important complement, we further discuss three important issues: 1) the influence of Goos–Hänchen shift on numerical aperture (NA) measurement; 2) comparison of one-dimension and two-dimension identification algorithms; and 3) comparison of center locating using Fourier correlation analysis (FCA) and Hough transformation (HT) algorithms. [ABSTRACT FROM AUTHOR]

We present a general-purpose end-to-end image chain simulation (ICS) that enables to assess the image quality of a satellite imager for Earth observations. The image chain consists of four main components: radiometry, atmosphere, optics, and detector. In particular, ICS first computes the input radiance from the reflectance values of a high-resolution input, and then calculates the image radiance by using the optical transfer function (OTF) of the overall system. This OTF contains all the distortion effects due to atmosphere, optics, and detector. Finally, the signal on the detector, including the noise term, is computed and converted to digital counts. To evaluate the overall image quality, metrics such as peak signal-to-noise ratio and minimum resolvable contrast are used. To illustrate the utility and versatility of the developed ICS, several analyses are also performed that demonstrate the system performance of a generic satellite imagery. Our development provides a unified framework for the ICS developers of spaceborne Earth-observing systems. Such a complete end-to-end ICS is crucial for the effective development of an Earth observation satellite, especially in the design and test phases. [ABSTRACT FROM AUTHOR]

Breaking through diffraction limit at terahertz frequencies is currently performed with the near-field scanning optical microscopy, which suffers from low integration and sensitivity limitations. In this paper, a solid-state superresolution imaging device in 130-nm SiGe BiCMOS technology operating around 534–562 GHz is presented. The device exhibits a single-chip integration of the complete imaging functionality, including a tunable CW illumination source, near-field sensing, and power detection with a high response of up to 9.65 \mu \textA and a noise-equivalent power of around 15–21 pW /\sqrt \text Hz at 60 kHz. Here, the stopband characteristics of a novel cross-bridged double split-ring resonator are exploited as an object-tunable transmission gate between a 3-push Colpitts oscillator and a simple HBT power detector. The resonator features a 3-D topography to achieve high-spatial confinement of the surface near-fields and is capable of resolving structural details with an estimated lateral resolution down to 10–12 \mu \textm . For a separate antenna-coupled oscillator breakout, a radiated power of up to 28.2 \mu \textW was measured. Furthermore, a 2-D raster-scanned superresolution image with a remarkable signal-to-noise ratio of 42 dB was captured for the device operating even at dc. [ABSTRACT FROM PUBLISHER]

After the successful completion of the SIDDHARTA experiment run with crab waist collisions, the electron-positron collider DA\Phi NE has started routine operations for the KLOE-2 detector. Similarly to the SIDDHARTA configuration, the new interaction region exploits the crab waist collision scheme, but features certain complications including the experimental detector solenoid, compensating anti-solenoids, and tilted quadrupole magnets, that lead to significant coupling of the horizontal and vertical betatron motion. It is not immediately obvious if the crab waist scheme would be as efficient in the strongly coupled case as it was in the uncoupled configuration. We have performed simulations of beam-beam interactions in the collider taking into account the real machine nonlinear lattice. In particular, we have evaluated the effect of crab waist sextupoles and beam-beam interactions on the collider dynamical aperture and energy acceptance. A new betatron tune working point has been proposed for the DA\Phi NE electron ring, and its implementation resulted in more than 20% background reduction and injection efficiency improvement. Exploiting this working point has allowed reaching the best present luminosity of 2.0 \times 10^32\ \cm^-2\ \s^-1. The numerical simulations have shown that for the given bunch currents in collision, the powering of the crab waist sextupoles should decrease the beam core blow up by a factor of 2 indicating that even higher luminosity can be achieved in DA\Phi NE thus encouraging further collider optimization. [ABSTRACT FROM PUBLISHER]

Motivated by classical coincidence imaging which has been realized in optical systems, an instantaneous microwave-radar imaging technique is proposed to obtain focused high-resolution images of targets without motion limitation. Such a radar coincidence imaging method resolves target scatterers based on measuring the independent waveforms of their echoes, which is quite different from conventional radar imaging techniques where target images are derived depending on time-delay and Doppler analysis. Due to the peculiar features of coincidence imaging, there are two potential advantages of the proposed imaging method over the conventional ones: 1) shortening the imaging time to even a pulse width without resolution deterioration so as to improve the performance of processing noncooperative targets and 2) simplifying the receiver complexity, resulting in a lower cost and platform flexibility in application. The basic principle of radar coincidence imaging is to employ the time-space independent detecting signals, which are produced by a multitransmitter configuration, to make scatterers located at different positions reflect independent waveforms from each other, and then to derive the target image based on the prior knowledge of this detecting signal spatial distribution. By constructing the mathematic model, the necessary conditions of the transmitting waveforms are analyzed for achieving radar coincidence imaging. A parameterized image-reconstruction algorithm is introduced to obtain high resolution for microwave radar systems. The effectiveness of this proposed imaging method is demonstrated via a set of simulations. Furthermore, the impacts of modeling error, noise, and waveform independence on the imaging performance are discussed in the experiments. [ABSTRACT FROM PUBLISHER]

This paper introduces a new type of icing detector for aircraft applications. Unlike the well-known icing detectors that are based on optics, the new detector uses \alpha particles. An \alpha-particle source is attached to the wing of the aircraft, and a detector that mainly depends on a MOSFET transistor is placed a few centimeters away from the source. As the \alpha particles strike the detector, they deposit their positive charges on the gate of the MOSFET (n-channel), and the transistor turns ON. If, however, a layer of ice builds up on the wing and prevents the \alpha particles from reaching the detector, the MOSFET shuts OFF. The new detector is more reliable than optics-based detectors because it is an integral part of the wing and hence cannot miss the formation of ice. [ABSTRACT FROM PUBLISHER]

In order to improve the safety, lifetime, and energy efficiency of turbomachines, the dynamic behavior of the rotor has to be analyzed. Blade vibrations have to be monitored during operation to optimize the rotor design and to validate numerical models. However, measuring the vibration amplitude and frequency of the blades is a challenging task for metrology, since the blades to be measured are rotating quickly, and noncontact measurements are demanded. To solve this problem, we present a measurement system consisting of four laser Doppler sensors that have been mounted around the circumference of the rotor. These sensors measure simultaneously and contactlessly the in-plane velocity and the out-of-plane position of laterally moving objects. By analyzing the variation of the blade tip velocities, the vibration amplitude and frequency of the blades were estimated. Blade vibration measurements down to amplitudes of only 20 \mum in tangential direction have been carried out. We achieved a standard uncertainty of approximately 400 nm for these experiments. [ABSTRACT FROM PUBLISHER]

We present a 3-D surface profiling method for microlenses that utilizes a Shack–Hartmann wavefront sensor. This method applies to both solid microlenses and liquid–liquid interfaces in liquid microlenses. The wavefront at the aperture stop of a microlens is measured by a Shack–Hartmann wavefront sensor and is then used to calculate the 3-D surface profile of the microlens. Three types of microlenses—a photoresist microlens, a hydrogel-driven tunable liquid lens, and an electrowetting-driven tunable liquid lens—were fabricated and measured. The variable-focus liquid lenses were tested within a wide focal length range. The obtained surface profiles were fitted to spherical and conical surface models to study their geometrical properties. The photoresist microlens was found to be approximately spherical. For the hydrogel-driven microlens, the profile was smooth and nearly spherical at the center but became steep and linear at the aperture edges. The electrowetting-driven liquid lens was also fitted better with the conical model, and its conic constant was determined. The obtained surface profiles were used to estimate the optical properties of microlenses in an optical analysis software package. The comparison between the simulation and experiment results indicated that the accuracy of the estimation is rough and the error could be due to the wavefront measurement and surface fitting approximation.\hfill[2011-0321.R1] [ABSTRACT FROM PUBLISHER]

A computational camera uses a combination of optics and processing to produce images that cannot be captured with traditional cameras. In the last decade, computational imaging has emerged as a vibrant field of research. A wide variety of computational cameras has been demonstrated to encode more useful visual information in the captured images, as compared with conventional cameras. In this paper, we survey computational cameras from two perspectives. First, we present a taxonomy of computational camera designs according to the coding approaches, including object side coding, pupil plane coding, sensor side coding, illumination coding, camera arrays and clusters, and unconventional imaging systems. Second, we use the abstract notion of light field representation as a general tool to describe computational camera designs, where each camera can be formulated as a projection of a high-dimensional light field to a 2-D image sensor. We show how individual optical devices transform light fields and use these transforms to illustrate how different computational camera designs (collections of optical devices) capture and encode useful visual information. [ABSTRACT FROM AUTHOR]

The Visible and Infrared Hyperspectral Imager (VIHI) is one of the three optical heads of the Spectrometers and Imagers for MPO BepiColombo Integrated Observatory SYStem (SIMBIO-SYS) experiment onboard European Space Agency's BepiColombo cornerstone mission to Mercury. The other two optical heads of SIMBIO-SYS are a stereo camera and a high-resolution image camera. The experiment is designed to scan the Hermean surface from a polar orbit with the three channels to map the physical, morphological, tectonic, and compositional properties of the planet. The main scientific objectives of SIMBIO-SYS are the study of Mercury's surface geology and stratigraphy, the surface composition, the regolith properties, the crustal differentiation, impact, and volcanic processes. The VIHI experiment uses a high-performance optical layout (Schmidt telescope and spectrometer in Littrow configuration) which allows investigating the 400–2000-nm spectral range with 256 spectral channels (6.25 nm/band sampling). The instrument has an instrument field of view (FOV) of 250 \mu\rad corresponding to a spatial scale of about 100 m/pixel at periherm and 375 m at apoherm. The instrument operates in pushbroom configuration, sampling the surface of Mercury with an FOV of 64 \times 0.25 mrad. The main technical challenges of this experiment are focal-plane design (cadmium–mercury–telluride thinned to improve the efficiency at visible wavelengths), short dwell time (from about 40 ms at equator to about 100 ms at poles), thermal control, mechanical miniaturization, radiation hardening, high data rate, and compression. A description of the internal calibration unit concept and functionalities is given. [ABSTRACT FROM AUTHOR]

Multiplicative noise (also known as speckle noise) models are central to the study of coherent imaging systems, such as synthetic aperture radar and sonar, and ultrasound and laser imaging. These models introduce two additional layers of difficulties with respect to the standard Gaussian additive noise scenario: 1) the noise is multiplied by (rather than added to) the original image; 2) the noise is not Gaussian, with Rayleigh and Gamma being commonly used densities. These two features of multiplicative noise models preclude the direct application of most state-of-the-art algorithms, which are designed for solving unconstrained optimization problems where the objective has two terms: a quadratic data term (log-likelihood), reflecting the additive and Gaussian nature of the noise, plus a convex (possibly nonsmooth) regularizer (e.g., a total variation or wavelet-based regularizer/prior). In this paper, we address these difficulties by: 1) converting the multiplicative model into an additive one by taking logarithms, as proposed by some other authors; 2) using variable splitting to obtain an equivalent constrained problem; and 3) dealing with this optimization problem using the augmented Lagrangian framework. A set of experiments shows that the proposed method, which we name MIDAL (multiplicative image denoising by augmented Lagrangian), yields state-of-the-art results both in terms of speed and denoising performance. [ABSTRACT FROM AUTHOR]

Satellite data from the Surrey Satellite Technology Limited (SSTL) United Kingdom (UK) Disaster Monitoring Constellation (DMC) were assessed for geometric and radiometric quality. The UK-DMC Surrey Linear Imager 6 (SLIM-6) sensor has a 32-m spatial resolution and a ground swath width of 640 km. The UK-DMC SLIM-6 design consists of a three-band imager with green, red, and near-infrared bands that are set to similar bandpass as Landsat bands 2, 3, and 4. The UK-DMC data consisted of imagery registered to Landsat orthorectified imagery produced from the GeoCover program. Relief displacements within the UK-DMC SLIM-6 imagery were accounted for by using global 1-km digital elevation models available through the Global Land One-km Base Elevation (GLOBE) Project. Positional accuracy and relative band-to-band accuracy were measured. Positional accuracy of the UK-DMC SLIM-6 imagery was assessed by measuring the imagery against digital orthophoto quadrangles (DOQs), which are designed to meet national map accuracy standards at 1 : 24 000 scales; this corresponds to a horizontal root-mean-square accuracy of about 6 m. The UK-DMC SLIM-6 images were typically registered to within 1.0-1.5 pixels to the DOQ mosaic images. Several radiometric artifacts like striping, coherent noise, and flat detector were discovered and studied. Indications are that the SSTL UK-DMC SLIM-6 data have few artifacts and calibration challenges, and these can be adjusted or corrected via calibration and processing algorithms. The cross-calibration of the UK-DMC SLIM-6 and Landsat Enhanced Thematic Mapper Plus was performed using image statistics derived from large common areas observed by the two sensors. [ABSTRACT FROM AUTHOR]

In many surveillance applications, high resolution imaging sensors provide imagery over large areas for operators to visually determine the presence of threats. Two significant challenges are: 1) the large amount of image data can be taxing for a human operator over a long period of time (as well as for other system resources such as network bandwidth), and 2) relatively expensive optics and large focal plane arrays are needed to produce high quality images. Compressed sensing holds the promise for radically novel sensors that can perfectly reconstruct Images using comparatively simple hardware and considerably fewer samples of data than required by the otherwise general Shannon sampling theorem. It has been shown by Candes, Romberg, and Tao [1], Donoho [2], and others that by measuring relatively few projections of a scene on random vectors, iterative greedy algorithms and basis pursuit techniques that minimize the L1 norm of the solution vector can perfectly reconstruct the entire image. To reduce the load on the human operator, however, It Is also desirable to cue regions of the image where objects of interest may exist. Towards this end, we are interested here in selectively imaging Interesting objects in a scene, without necessarily seeking perfect reconstruction of the whole image. We show that our goals are achieved by minimizing a modified L2-norm criterion when the reconstruction of only specific objects is of interest. We achieve this by introducing prior knowledge about objects in a known basis as soft constraints in the reconstruction equation. At first blush it may appear that the same could be achieved by measuring projections of the objects directly on the basis set. However, this trivial solution requires that the basis functions be changed for every object; thus, the solution is not suitable for practical applications. We show that the proposed approach takes advantage of the simplicity, elegance, and generality of the compressed sensing architecture by achieving object-specific reconstruction using random projection on simple binary masks. Most importantly, a single set of random projective measurements can be used to algorithmically reconstruct any object of interest without requiring explicit and repeated measurements on different basis sets that vary with the object of interest. Clearly, this has significant implications on system issues and practical consideration such as hardware complexity and time required for searching for objects over a large number of classes. Our assumption that some information is known about specific objects of interest is distinctly different from the original theory of compressed sensing as postulated by Candes, et al. [1] and Donoho [2]. The proposed method is not an alternative when the perfect reconstruction of arbitrary images is required, but nevertheless operates within the same framework by extracting information from compressive measurements. The proposed method yields a simple closed-form analytical solution that does not require iterative processing. Objects can be meaningfully sensed in considerable detail while heavily compressing the scene elsewhere. Essentially, this embeds the object detection and clutter discrimination function in the sensing and imaging process. To the best of our knowledge, this is the first application of a compressed sensing architecture that is explicitly tailored for surveillance scenarios where the ability to find specific objects is of interest. [ABSTRACT FROM AUTHOR]

Preliminary studies have shown the effectiveness of multivariate analysis (MVA) for drug identification from energy-dispersive X-ray diffraction patterns. A statistical model to predict drug content from the diffraction profile of a sample of mixed composition was developed by applying MVA to both experimental and simulated data. Separate data-sets were used for building and testing the models. Both experimental and simulated data were used and the MVA predictions compared. Experimental data included diffraction patterns from small (5 mm diameter) drug samples with various cutting agents, acquired with a HPGe detector; simulated data included diffraction patterns of samples including materials simulating drugs (i.e., materials featuring sharp diffraction peaks in the relevant momentum transfer range) and typical packaging materials. Both a HPGe detector (energy resolution 0.7 keV at 59.5 keV) and a CZT detector (energy resolution 4 keV at all energies) were simulated. MVA was used to predict the drug content. In all cases different statistics were applied to assess the detection limits of the models. Multivariate analysis has proved effective in both identifying the presence of a drug and its concentration. Due to the large contribution to peak broadening given by angular resolution, no significant decrease in accuracy has been found when using CZT with respect to HPGe data. [ABSTRACT FROM AUTHOR]

Rapid and accurate detection and identification of biological agents is an objective of various national security programs. Detection in general is difficult owing to natural clutter and anticipated low concentrations of subject material. Typical detection architectures comprise a nonspecific trigger, a rapid identifier, and a confirming step, often in a laboratory. High-confidence identification must be made prior to taking action, though this must be traded against regrets stemming from delay. Sensing requirements are best established by positing plausible scenarios, two of which are suggested herein. Modern technologies include the use of elastic scatter and ultraviolet laser-induced fluorescence for triggering and standoff detection. Optical and nonoptical techniques are used routinely in analyzing clinical samples used to confirm infection and illness resulting from a biological attack. Today, environmental sensing serves at best as an alert to medical authorities for possible action, which would include sample collection and detailed analysis. This paper surveys the state of the art of sensing at all levels. [ABSTRACT FROM AUTHOR]

Sensor systems provide a critical capability for maintaining situational awareness for defense and security applications. Advances in sensor system technology over the last fifty years have created sophisticated systems to collect, detect, process, and respond to radiation over much of the electromagnetic spectrum. In this article, we discuss the physical processes important to the design of photonic sensing, review programs advancing sensor technologies at the Defense Advanced Research Projects Agency, and provide some insight to future capabilities. [ABSTRACT FROM AUTHOR]

For the first time, the response function to high-energy photons of a 3×3 matrix comprising large volume LYSO crystals was measured using energy marked photons provided by the tagged photon facility of MAMI. The crystal quality was determined based on the optical transparency, the intrinsic radioactivity and the luminescence yield. Energy and time resolutions for photons up to 490 MeV photon energy have been deduced from the reconstruction of the electromagnetic shower deposited into the crystal array and the data deliver very promising results. [ABSTRACT FROM AUTHOR]

Analysis of radar scattering from targets with curved boundaries, such as objects comprising cylindrical and conical shapes, is important to many aerospace applications. The radar return is composed of a well-characterized physical optics response in the illuminated region where the transmitter and receiver are not shadowed by the object, and a combination of modal responses (e.g., creeping waves and edge-diffracted fields) in the shadow region. The modal responses have longer down-range than scattering centers located on the object, and therefore, produce extended (or off-body) returns in ISAR images, which are not well-understood. However, these returns are strongly dependent on local features of the object, and thus contain valuable information with regard to the target's geometrical and physical composition. Multiple reflections from illuminated facets, as well as multiply diffracted waves, can also add coherently in the direction of the receiver and produce such returns. This paper applies a robust, coherent-processing system identification technique, originally developed for radar sensor fusion, to estimate amplitude and phase of the scatterers that characterize extended returns in the target signature. Examples are presented that highlight the extraction of creeping waves using measured data on a cone-sphere. [ABSTRACT FROM AUTHOR]

Alternative models are discussed for the determination of the interior irradiation contribution to the radar cross section (RCS) of open-ended cavities. Typical applications of practical interest include radiation field prediction of open-ended waveguides and signature prediction of jet engine air intakes and exhaust outlets. It is shown and explained why the classic perfectly conducting (PEC) ground plane (GP) model sometimes predicts measured cavity RCS very poorly. Examples where PEC GP model predictions are 5 dB or more off are provided. Verifications that the used PEC GP model is correctly implemented are provided. A physical optics based modification of the classic PEC GP model is provided and explained. A novel model where the cavity aperture forms an opening in an infinite radar absorbing (IBC) screen is proposed verified and validated. The IBC model resembles the common experimental set-up, and poses an efficient novel halfs-pace type replacement model approximating a full space setting. The modified PEC GP model or the IBC model can be used interchangeably for cavities with electrically large apertures. [ABSTRACT FROM AUTHOR]

In master-slave teleoperation applications that deal with a delicate and sensitive environment, it is important to provide haptic feedback of slave/environment interactions to the user's hand as it improves task performance and teleoperation transparency (fidelity), which is the extent of telepresence of the remote environment available to the user through the master-slave system. For haptic teleoperation, in addition to a haptics-capable master interface, often one or more force sensors are also used, which warrant new bilateral control architectures while increasing the cost and the complexity of the teleoperation system. In this paper, we investigate the added benefits of using force sensors that measure hand/master and slave/environment interactions and of utilizing local feedback loops on the teleoperation transparency. We compare the two-channel and the four-channel bilateral control systems in terms of stability and transparency, and study the stability and performance robustness of the four-channel method against nonidealities that arise during bilateral control implementation, which include master-slave communication latency and changes in the environment dynamics. The next issue addressed in the paper deals with the case where the master interface is not haptics capable, but the slave is equipped with a force sensor. In the context of robotics-assisted soft-tissue surgical applications, we explore through human factors experiments whether slave/environment force measurements can be of any help with regard to improving task performance. The last problem we study is whether slave/environment force information, with and without haptic capability in the master interface, can help improve out- comes under degraded visual conditions. [ABSTRACT FROM AUTHOR]

A Gaussian beam summation (GBS) representation for half plane diffraction of an incident two dimensional Gaussian beam (GB) that hits arbitrarily close to the edge is presented. The scattered field is expanded into an angular spectrum of GBs that emerge from the edge. We derive asymptotic expressions for the diffracted beams amplitudes, that are valid uniformly as a function of the distance of the incident beam from the edge and of the scattering beams angles. In the limiting cases when the incident GB hits far from the edge, these expressions reduce uniformly to a geometrical optics model plus a weak edge diffractions due to the off-axis beam field that hits the edge. Applications to GBS modeling of indoor propagation are discussed. [ABSTRACT FROM AUTHOR]

In this paper, we report our systematic study of a promising absolute-calibration technique of analog photodetectors based on the properties of parametric down conversion. Our formal results and a preliminary uncertainty analysis show that the proposed method can be effectively developed with interesting applications to metrology. [ABSTRACT FROM AUTHOR]

This paper presents a synthetic aperture radar (SAR) simulator that is able to generate polarimetric SAR (POLSAR) and polarimetric inverse SAR data of complex targets. It solves the electromagnetic problem via high-frequency approximations, such as physical optics and the physical theory of diffraction, with notable computational efficiency. In principle, any orbital monostatic sensor working at any band, resolution, and operating mode can be modeled. To make simulations more realistic, the target's bearing and speed are considered, and for the particular case of vessels, even the translational and rotational movements induced by the sea state. All these capabilities make the simulator a powerful tool for supplying large amounts of data with precise scenario information and for testing future sensor configurations. In this paper, the usefulness of the simulator on vessel classification studies is assessed. Several simulated polarimetric images are presented to analyze the potentialities of coherent target decompositions for classifying complex geometries, thus basing an operational algorithm. The limitations highlighted by the results suggest that other approaches, like POLSAR interferometry, should be explored. [ABSTRACT FROM AUTHOR]

Demosaicing is a process of obtaining a full-color image by interpolating the missing colors of an image captured from a single sensor color filter array. This paper provides an effective and low-complexity iterative demosaicing algorithm applying a weighted-edge interpolation to handle green pixels followed by a series of color-difference interpolation to update red, blue, and green pixels. Based on our experiments of images, we enable the algorithm a well-designed stopping condition and predetermine the proper weights of interpolation. Experimental results show that the proposed method performs much better than three state-of-the-art demosaicing techniques in terms of both computational cost and image quality. In comparison to the algorithm of successive approximation, the algorithm proposed here reduces mean squared error up to 14.5% while requiring computational cost only 22% on average. That is, it takes less time but performs better. [ABSTRACT FROM AUTHOR]

Phase contrast imaging (PCI) is an internal reference beam interferometry technique which provides a direct image of line integrated plasma density fluctuations. The method has been used with great success to measure waves and turbulence in magnetically confined high temperature plasmas. The principle of PCI was developed in optics in the 1930s by the Dutch physicist Zernike, leading to the development of phase-contrast microscopy [1], [17]. The technique allows one to detect the variation of the index of refraction of a dielectric medium (such as a plasma) due to the presence of waves or turbulent fluctuations. The image produced by the introduction of a phase plate in the beam path, and subsequently imaging the expanded laser beam onto a detector array can be used to calculate wavelengths and correlation lengths of fluctuations in high temperature plasmas. In this paper, the principle of PCI is summarized and examples of measurements from the DIII-D and Alcator C-Mod tokamak plasmas are given. [ABSTRACT FROM AUTHOR]

Identification of buried antipersonnel landmines with ground penetrating radar (GPR) establishes a need for application-specific scattering models and associated estimation algorithms relating the measured scattered field to target characteristics such as size, material composition and burial depth. To this end, starting from integral representations of the scattered field, we derive frequency- and time-domain convolutional models for the GPR response of buried dielectric and metal mine-like targets, including simple analytical expressions for the target transfer function/impulse response. The main steps in the derivation are the linearization of the scattering problem by either the Born or the Physical Optics approximation, the application of a new far-field backscattering representation of the half-space Green's tensor, and the introduction of point source/receiver models for the GPR antennas and the receiver chain. Using three-dimensional finite-difference time-domain (FDTD) and measured data examples, we illustrate the validity of the convolutional models and how they can be used to characterize buried targets. For the characterization, we make use of a deconvolution algorithm, termed "subset selection deconvolution," which uses our target impulse response approximations as a priori information on the form of the impulse response to be estimated. The results demonstrate the possibility to determine target size and depth from the estimated impulse response with millimeter accuracy under laboratory conditions, both of which are valuable information for Iandmine identification. [ABSTRACT FROM AUTHOR]

We describe a generalized inverse synthetic aperture radar (ISAR) process that performs well under a wide variety of conditions common to the naval ISAR tests of large vessels. In particular, the generalized ISAR process performs well in the presence of moderate intensity ship roll. The process maps localized scatterers onto peaks on the ISAR plot. However, in a generalized ISAR plot, each of the two coordinates of a peak is a fixed linear combination of the three ship coordinates of the scatterer causing the peak. Combining this process with interferometry will then provide high-accuracy three-dimensional location of the important scatterers on a ship. We show that ISAR can be performed in the presence of simultaneous roll and aspect change, provided the two Doppler rates are not too close in magnitude. We derive the equations needed for generalized ISAR, both roll driven and aspect driven, and test them against simulations performed in a variety of conditions, including large roll amplitudes. [ABSTRACT FROM AUTHOR]

We consider the problem of estimating the dispersion of a wave field from data recorded by a linear array of geophones. The fact that the data we are looking at may contain several propagating waves make this even more challenging. In this paper, a new algorithm is proposed to solve this issue. Currently, there are two methods for estimating wave dispersion described in the literature. The first method estimates the group delay function from the time-frequency representation (TFR) of each sensor separately. It is efficient as long as the patterns of the different waves do not overlap in the time-frequency plane. The second method estimates the dispersion from the two-dimensional (2-D) Fourier transform of the profile (or more generally from a velocity-frequency representation). This assumes that the dispersion is constant along the entire sensor array. It is efficient as long as the patterns of the waves do not overlap in the frequency domain. Our method can be thought of as a hybrid of the above two methods as it is based on the construction of a TFR where the energy of waves that propagate at a selected velocity are amplified. The primary advantage of our algorithm is the use of the velocity variable to separate the patterns of the propagating waves in the lime-frequency plane. When applied to both synthetic and real data, this new algorithm gives much improved results when compared with other standard methods. [ABSTRACT FROM AUTHOR]

This paper contains theoretical and experimental results on the application of the time-reversal process to acoustic communications in order to improve data telemetry in the ocean. A coherent underwater acoustic communication system must deal with the inter-symbol interference caused by the time-varying, dispersive, shallow-water ocean environment. An approach is demonstrated that takes advantage of the focal properties of time reversal. The spatial and temporal compression available at the time-reversal focus mitigates channel fading, reduces the dispersion caused by the channel, and increases the signal strength. Thus, a time-reversal communication system does not require spatial diversity at the receiver, i.e., an array of receiving sensors~ but takes advantage of spatial diversity at the transmitter. The time-reversal communications system concept is demonstrated using experimental data collected in shallow water. Data telemetry bit rates of 500 bps (BPSK) and 1000 bps (QPSK) with bit error rates of 0 out of 4976 bits and 254 out of 9953 hits, respectively, were obtained when transmitting to a receiver at a distance of 10 km, with a carrier frequency of 3500 Hz, and a 500 Hz bandwidth. in a shallow-water upslope region, bit error rates of 15 out of 4976 bits and 14 out of 4976 bits were achieved over the same distance. In neither case was complex processing at the receiver used (i.e., channel equalization, error correction coding). Time-reversal transmissions are intercompared with single source and broadside transmissions and shown to have superior results in both range independent and dependent bathymetries. The time-reversal performance appears limited by self-generated inter-symbol interference, in addition, an initial look at the application of a single channel adaptive channel equalizer to received time-reversal communication sequences is presented. The same properties that are beneficial to a single channel receiver are also beneficial to adaptive channel equalization. A single channel RLS DFE equalizer is cascaded with the received time-reversal sequences and shown to further reduce scatter in the I/Q plane. The bit error rate decreased in all but one of the cases. [ABSTRACT FROM AUTHOR]

Some existing closed-form expressions for target echo and reverberation, assuming classical mode-stripping and Lambert's law in isovelocity water, are extended to the case of uniform slope bathymetry combined with range-independent linear sound speed and bistatic geometry. The analytical, or extremely fast numerical, calculation of signal-to-reverberation-ratio provides insight useful for sonar design, and operational research. There are three types of path, each of which may be important at some range: Those that only interact with one boundary, those that always interact with both boundaries and those that sometimes interact with both. Each provides a separate closed-form contribution. The earlier finding, that with Lambert's law the reverberation tends to follow the same range trend as the target echo, is slightly modified by the addition of refraction. The stronger reverberation from the low sound speed side of the duct tends to fall off slightly less slowly than the target echo according to the strength of the refraction. Some graphical examples show that the very large parameter space can be handled very easily. [ABSTRACT FROM AUTHOR]

We report the growth and fabrication of bound-to- bound In0.53 Ga0.47As-InP quantum-well infrared photodetectors using metal-organic vapor phase epitaxy. These detectors have a peak detection wavelength of 8.5 μm. The peak responsivities are extremely large with Rpk = 6.9 A/W at bias voltage Vb = 3.4 V and temperature T = 10 K. These large responsivities arise from large detector gain that was found to be gn = 82 at Vb = 3.8 V from dark current noise measurements at T = 77 K and gp = 18.4 at Vb = 3.4 V from photoresponse data at T = 10 K. The background-limited temperature with F/1.2 optics is TBLIP = 65 K for 0 < Vb ⩽ 3.4 V. The highest value of peak detectivity is DΛ* = 5.4 × 109 cm√ Hz/W at Vb = 2.9 V and T = 77 K, while for T < TEMP = 65 K, the back- ground-limited detectivity, which exhibits negligible bias dependence, is DBLIP* = 3 × 1010 cm√Hz/W. [ABSTRACT FROM AUTHOR]

Tungsten thin films can form in one of two crystal structures: alpha (bcc), with a superconducting transition temperature (Ta) of 15 mK, and beta (A15), with a Tc between 1 and 4 K. Films with intermediate us are composed of both alpha and beta phases. We have investigated how to tune the film Tc in order to obtain certain values (Tc ∼ 100 mK) suitable for the fabrication of photon number resolving transition-edge sensor (TES) and arrays of TES detectors for astronomical and quantum information applications. Variation of deposition conditions, and also the choice of the underlayer/coating for equal deposition conditions, affect the TcS of tungsten films. We have used x-ray diffraction to determine the structure of tungsten thin films and film stress. The results indicates that the film stress state depends on the underlying substrate and coating. To understand the variation of Tc values and to allow precise tuning of these values, we have investigated substrates and coatings for tungsten film multilayer stacks and determined tungsten film stress by x-ray diffraction at both room temperature and 8K. [ABSTRACT FROM AUTHOR]

The purpose of this study is to investigate Synthetic Aperture Radar (SAR) image segmentation into a given but arbitrary number of gamma homogeneous regions via active contours and level sets. The segmentation of SAR images is a difficult problem due to the presence of speckle which can be modeled as strong, multiplicative noise. The proposed algorithm consists of evolving simple closed planar curves within an explicit correspondence between the interiors of curves and regions of segmentation to minimize a criterion containing a term of conformity of data to a speckle model of noise and a term of regularization. Results are shown on both synthetic and real images. [ABSTRACT FROM AUTHOR]

This paper presents a method of unsupervised enhancement of pixels homogeneity in a local neighborhood. This mechanism will enable an unsupervised contextual classification of multispectral data that integrates the spectral and spatial information producing results that are more meaningful to the human analyst. This unsupervised classifier is an unsupervised development of the well-known supervised extraction and classification for homogenous objects (ECHO) classifier. One of its main characteristics is that it simplifies the retrieval process of spatial structures. This development is specially relevant for the new generation of airborne and spaceborne sensors with high spatial resolution. [ABSTRACT FROM AUTHOR]

In support of hyperspectral sensor system design and parameter tradeoff investigations, an analytical end-to-end remote sensing system performance forecasting model has been extended to cover the visible through Iongwave infrared portion of the optical spectrum (0.4-14 μm). The model uses statistical descriptions of surface spectral reflectances/emissivities and temperature variations in a scene and propagates them through the effects of the atmosphere, the sensor, and processing transformations. A resultant system performance metric is then calculated based on these propagated statistics. This paper presents theory for the analytical transformation of surface statistics to at-sensor spectral radiance statistics for a downward-looking hyperspectral sensor observing both reflected sunlight and thermally emitted radiation. Comparisons of the model predictions with measurements from an airborne hyperspectral sensor are presented. Example parameter trades are included to show the utility of the model for applications in sensor design and operation. [ABSTRACT FROM AUTHOR]

One of the instruments on the sun-synchronous Thrra (EOS AM) and Aqua (EOS PM) spacecraft, the Moderate Resolution Spectroradiometer (MODIS), obtains calibration data once during every orbit. Observations of the sun permit corrections to observations of the earth during the ensuing orbit. Although the instrument was designed to receive uniform sunlight over the entire surface of its detector, the sunlight was in fact not uniform. While this did not adversely affect the calibration, it nonetheless implied a lack of understanding of how the optical system really functioned. To lean what was wrong, NASA used an optical ray-tracing program on a DEC Alpha computer. The results correlated well with the observations made by the instrument itself, hut it took nearly two weeks to complete the computer simulation, a discouragingly long time. This paper describes the algorithm and its implementation in a system with multiple digital signal processor (DSP) chips operating in parallel. Timing data show a highly linear relationship between the number of DSPs present and the speed of the computation. Administrative overhead is negligible compared to the time taken to compute ray trajectories. This implies that many more than just four DSPs could be harnessed before administrative overhead would begin to be significant. [ABSTRACT FROM AUTHOR]

A novel data detection scheme is proposed for two-dimensional data storage systems. This scheme is designed to reduce the complexity of two-dimensional Viterbi detector by constraining intertrack interference to be causal and by exploiting the principle of decision feedback Its application to the two-dimensional optical data storage system is investigated, and further simplifications are also developed. [ABSTRACT FROM AUTHOR]

We have developed a large-format CdZnTe pixel detector with custom, low-noise ASIC readout, for astrophysical applications. In particular, this detector is targeted for use in the High-Energy Focusing Telescope (HEFT), a balloon-borne experiment with focusing optics for 20-70 keV. The detector is a 24 × 44 pixel array of 498-μm pitch. As a focal plane detector, uniformity from pixel to pixel is very desirable. In this paper, we present the characterization of some detector properties for the 1056 pixels on the HEFT detector. These properties include electronic noise, leakage current, spectral resolution, and count rate. [ABSTRACT FROM AUTHOR]

We describe work that extends three-dimensional (3-D) patterned overlay high-density interconnect (HDI) to high-performance imaging applications. The work was motivated by the rigorous requirements of the multiple-pulse imager for dynamic proton radiography. The optical imager has to provide large (>90%) optical fill factor, high quantum efficiency, 200-ns inter-frame time interval, and storage for >32 frames. In order to accommodate the massively parallel electronics including the signal storage for a large number of frames, it is necessary to provide novel 3-D interconnect and packaging architectures. Recently, a 3-D interconnect technology was successfully demonstrated to assemble a stack of 50 signal-processing chips into a cube. Each chip contained test connections (interconnect continuity only) simulating 160 channels of pixel read-out electronics. Test cube assemblies, based on these mock-up integrated circuits, have been fabricated to explore the feasibility of constructing functional cube arrays. A novel 3D integrated sensor-electronics (mirror-cube) imager architecture is proposed. We also briefly review progress in the custom fast image-processing electronics. [ABSTRACT FROM AUTHOR]

A flip-chip bonding technology has been developed for CdTe and (Cd,Zn)Te X-ray detectors. The aim of this paper is to choose a suitable chip interconnection technique for the fabrication of X-ray pixel detectors to fit the material requirements of detector grade CdTe and (Cd,Zn)Te. The proposed method is based on a flexible process, which permits the use of an eutectic PbSn alloy with a photoresist mask. A photosensitive polymer acts as a passivation layer and solder stop mask on CdTe or (Cd,Zn)Te. The proposed process provides the opportunity to do all process steps "in-house." [ABSTRACT FROM AUTHOR]

Preliminary research has shown that triboluminescent (TL) phosphors show promise for use as the active element in impact sensors. For ZnS:Mn, preliminary results indicate that impact energies greater than 1.6 Times; 10-2 J produced measurable TL light. A so-called "smart" structure with embedded TL material could be capable of determining whether a particle had struck, and record the relative intensity of its impact. In order to use such materials in space, we need to understand the radiation susceptibility of the TL phosphor. The corresponding proton dose required to reduce the proton-induced luminescence of ZnS:Mn to half of its initial value was found to be 9.02 × 1013 mm-2. This value will be used to help determine how incident protons affect the production of TL in ZnS:Mn. [ABSTRACT FROM AUTHOR]

Initial results are presented of a prototype optical transition radiation (OTR) detector under development at Fermi National Accelerator Laboratory. The purpose of this prototype detector is to evaluate the feasibility of using OTR imaging of intense proton (or antiproton) beams in transport lines for beam position and shape measurements. A secondary purpose is to develop experience in designing, constructing and operating a camera and optics system in high radiation environments. Measurements are made of 120 GeV proton beams with intensities up to 4.7 × 1012 particles. Data are presented of OTR with titanium and aluminum foils. [ABSTRACT FROM AUTHOR]

The performance for X-ray spectrometry of neon-xenon gas proportional scintillation counters using a CsI-coated microstrip plate in direct contact with the scintillation gas as a VUV photosensor is investigated for different neon-xenon mixtures. At best operation conditions, the detector gain can reach values about 50% higher than those achieved with pure xenon filling. The highest gains and the best energy resolutions are achieved for xenon contents around 40%. However, the achieved energy resolutions are similar to those achieved with pure xenon. As in pure xenon and argon-xenon mixture gas fillings, the detector performance is limited by optical positive feedback resulting from additional scintillation produced in the electron avalanche processes around the MSP anodes. The best energy resolutions are achieved for positive feedback gains in the range of 1.1 to 1.2. The performance achieved with neon-xenon mixtures is inferior to that achieved with argon-xenon mixtures. [ABSTRACT FROM AUTHOR]

This paper presents subsurface imaging techniques using the well-known MUSIC algorithm to localize point reflectors in cross-borehole radar arrangements. Radar signals received by a spatial array have to be decorrelated, in general, as a preprocessing step when the MUSIC algorithm is implemented. Since most of the decorrelation techniques are based on planar wave incidence model, it is difficult to apply the decorrelation technique for signals from radar targets in the near field of the array. In this paper, we introduce a decorrelation technique with transmitting and receiving array for targets near the array and apply the MUSIC algorithm for estimating the two dimensional position of the point targets in crosshole tomographic measurement. Further, an expanded version of the algorithm to eliminate the direct wave is also derived. Simulation results show that this method offers much higher resolution and accuracy than the conventional diffraction stack method. The paper also discusses the relationship between the SNR ratio and the minimum target separation to be resolved. [ABSTRACT FROM AUTHOR]

The fast physical optics (FPO) method for computing back-scattered fields over ranges of aspect angles and frequencies is extended to encompass double-bounce scattering. Computations are performed within the framework of the physical optics approximation appropriate in the high-frequency regime. The proposed algorithm is directly applicable to fixed angle bistatic configurations and a variety of double scattering settings. The method comprises two steps: 1) decomposition of the scatterer into subscatterers and computation of the scattering amplitudes of all pairs of subscatterers and 2) interpolation, phase correction, and aggregation of the scattering amplitude patterns of all subscatterer pairs into the pattern of the entire scatterer. The proposed method is especially suited for generating synthetic data for radar imaging simulations. [ABSTRACT FROM AUTHOR]