Showing papers in "Proceedings of SPIE in 1991"
TL;DR: In this article, the authors explore the representation of the human face by features based on the curvature of the face surface, such as the shape of the forehead, jawline, and cheeks, which are not easily detected from standard intensity images.
Abstract: This paper explores the representation of the human face by features based on the curvature of the face surface. Curature captures many features necessary to accurately describe the face, such as the shape of the forehead, jawline, and cheeks, which are not easily detected from standard intensity images. Moreover, the value of curvature at a point on the surface is also viewpoint invariant. Until recently range data of high enough resolution and accuracy to perform useful curvature calculations on the scale of the human face had been unavailable. Although several researchers have worked on the problem of interpreting range data from curved (although usually highly geometrically structured) surfaces, the main approaches have centered on segmentation by signs of mean and Gaussian curvature which have not proved sufficient in themselves for the case of the human face. This paper details the calculation of principal curvature for a particular data set, the calculation of general surface descriptors based on curvature, and the calculation of face specific descriptors based both on curvature features and a priori knowledge about the structure of the face. These face specific descriptors can be incorporated into many different recognition strategies. A system that implements one such strategy, depth template comparison, giving recognition rates between 80% and 90% is described.
209 citations
TL;DR: In this paper, two adaptive NUC techniques are discussed; one is a temporal highpass filter and the other involves a neural network with lateral interconnects to nearest neighbor pixels, both have similarities to biological retinal processing.
Abstract: With rapid advancements in infrared focal plane array (IRFPA) technology, greater demands are being placed on nonuniformity correction (NUC) techniques to provide near-BLIP performance over a wide dynamic range. Standard NUC techniques involve calibrating each detector using reference temperature sources before imaging the IRFPA. Usually the correction needs to be re-calibrated after a short period of time due to IRFPA drift or to adjust for changes in the level of background flux. Adaptive NUC techniques eliminate the need for calibration by continuously updating the correction coefficients based on radiance levels of the scene being viewed. In this manner, continuous compensation can be applied adaptively for individual detector non-idealities and background changes. Two adaptive NUC techniques are discussed; one is a temporal highpass filter and the other involves a neural network with lateral interconnects to nearest neighbor pixels. Both have similarities to biological retinal processing. Questions of implementation and stability are discussed and performance results are given for several test image sequences which were obtained from an MWIR HgCdTe array and a HIDAD uncooled array. We conclude that adaptive techniques will be very useful in future IRFPA sensors, primarily because of their ability to adapt over a wide range of background flux without calibration sources, but also because they can offer improved sensitivity under most operating conditions.
142 citations
TL;DR: Steps are taken toward the automatic, intensity-based recognition of human faces by constructing a vision system to automatically detect frontally-viewed human eyes in real data using a deformable template using a parameterized geometry and an intensity model.
Abstract: Steps are taken toward the automatic, intensity-based recognition of human faces by constructing a vision system to automatically detect frontally-viewed human eyes in real data. The eye is modeled using a deformable template that specifies a parameterized geometry and an intensity model. The fit of the template is measured by a cost-functional employing robust estimators, i.e., (alpha) -trimmed means and variances, to overcome highlights, shadows, nonrigid boundaries, noise, and other such difficulties. Recognition proceeds in three stages. First, candidate eyes are located by matching a simplified eye model against the responses of a robust, general purpose detector of intensity valleys and peaks. Second, the best fit of each candidate eye is found by minimizing the energy of a cost functional. Third, each candidate is accepted or rejected based on the amount of variance in the image data it explains.
114 citations
TL;DR: The mathematical theory of shape has a long history in the fields of differential geometry and topology as mentioned in this paper. But does this theory address the central problem of vision: finding the best data structure plus algorithm for storing a shape and later recognizing the same and similar shapes.
Abstract: The mathematics of shape has a long history in the fields of differential geometry and topology. But does this theory of shape address the central problem of vision: finding the best data structure plus algorithm for storing a shape and later recognizing the same and similar shapes. Several criteria may be used to evaluate this: does the data structure capture our intuitive idea of 'similarity'? does it allow reconstruction of typical shapes to compare with new input? One direction in which mathematics and vision have converged is toward multiscale analyses of visual signals and shapes. In other respects, however, the recognition process in animals shows features that still defy mathematical modeling.
113 citations
TL;DR: A new method for determining the rigid body transformation that describes this match is presented, which performs a least squares minimization of the distance between the camera-contour projection lines and the surface.
Abstract: The matching of 3-D anatomical surfaces to 2-D X-ray projections is an important problem in Computer and Robot Assisted Surgery. We present a new method for determining the rigid body transformation that describes this match. Our method performs a least squares minimization of the distance between the camera-contour projection lines and the surface. To correctly deal with projection lines that penetrate the surface, we minimize the square of the minimum signed distance along each line (distances inside the object are negative). To quickly and accurately compute distances to the surface, we represent the precomputed distance map using an octree spline whose resolution increases near the surface. The octree allows us to quickly find the minimum distance along each line using best-first search. We present experimental results of 3-D surface to 2-D projection matching, and also show how our method works for 3-D to 3-D surface matching.
109 citations
TL;DR: This paper discusses basic issues involved in the estimation of surface spectra from laboratory measurements, the development of physically-based spectral models, andThe estimation of finish parameters and their associated errors.
Abstract: This paper discusses basic issues involved in the estimation of surface spectra from laboratory measurements, the development of physically-based spectral models, and the estimation of finish parameters and their associated errors.
92 citations
TL;DR: Soft morphological operations are less sensitive to additive noise and to small variations in the shape of the objects to be filtered, so they give improved performance under certain conditions.
Abstract: New morphological operations, called soft morphological operations, are introduced. They maintain most of the properties of standard morphological operations, yet give improved performance under certain conditions. The main difference to standard morphological operations is that soft morphological operations are less sensitive to additive noise and to small variations in the shape of the objects to be filtered.
83 citations
TL;DR: In this article, a multiple correlated sampling technique was proposed to reduce the read noise of the focal plane array (FPA) by a factor of 9 over conventional readout techniques.
Abstract: The low background performance of most infrared systems has been limited by the read noise of the focal plane array (FPA). In many cases the cause has been attributed to the use of MOSFETS or to the detector itself. In this paper we describe a multiple correlated sampling technique and demonstrate noise improvements by a factor of 9 over conventional readout techniques in use today. The FPA under discussion is a `Source Follower per Detector' or SFD type readout structure; specifically, the Santa Barbara Research Center 58 X 62 InSb FPA and the Hughes Technology Center (HTC) 256 X 256 PtSi FPA. The quoted read noise for the SBRC FPA (typically 400 electrons rms) has been reduced to 45 electrons rms using this technique.
75 citations
TL;DR: A new approach to shape from shading is described based on a connection with a calculus of variations/optimal control problem that leads naturally to an algorithm for shape reconstruction that is simple, fast, provable convergent, and, in many cases, provably convergent to the correct solution.
Abstract: A new approach to shape from shading is described based on a connection with a calculus of variations/optimal control problem. The approach leads naturally to an algorithm for shape reconstruction that is simple, fast, provably convergent, and, in many cases, provably convergent to the correct solution. In particular, if the surface is known to be locally concave (or convex) at a singular point in the image, then the algorithm provably reconstructs the correct surface in a region around the singular point. The algorithm is robust against noise and, in contrast with standard variational algorithms, does not require regularization. An explicit representation is given for the surface: its height is expressed as the minimal cost for an optimally controlled trajectory. This representation makes the convergence analysis for the algorithm transparent, and allows it to be easily adapted to different situations in practice. Uniqueness of the reconstruction (under suitable conditions) is an immediate consequence. We focus primarily on the case of illumination from the camera direction. For this case, if the singular points at which the surface is locally concave have been identified, and their heights are known, then the algorithm provably reconstructs the original imaged surface. For general direction of illumination, there is a representation of the surface in terms of a differential game, and a slightly modified surface reconstruction algorithm. Finally, given a continuous image, the algorithm can be proven to converge to the continuous surface solution as the image sampling frequency is taken to infinity.
68 citations
TL;DR: A new technique for implementing fully complex spatial filters with a phase mostly deformable mirror device (DMD) light modulator is described, which combines two or more phase-modulating flexure-beam mirror elements into a single macro-pixel.
Abstract: A new technique for implementing fully complex spatial filters with a phase mostly deformable mirror device (DMD) light modulator is described. The technique combines two or more phase-modulating flexure-beam mirror elements into a single macro-pixel. By manipulating the relative phases of the individual sub-pixels within the macro-pixel, the amplitude and the phase can be independently set for this filtering element. The combination of DMD sub-pixels into a macro-pixel is accomplished by adjusting the optical system resolution, thereby trading off system space bandwidth product for increased filtering flexibility. Volume in the larger dimensioned space, space bandwidth-complex axes count, is conserved. Experimental results are presented mapping out the coupled amplitude and phase characteristics of the individual flexure-beam DMD elements and demonstrating the independent control of amplitude and phase in a combined macro-pixel. This technique is generally applicable for implementation with any type of phase modulating light modulator.
68 citations
TL;DR: In this paper, a batch-processed, totally planar, vertical-cavity top surface emitting GaAs/AlGaAs laser devices and arrays are studied experimentally.
Abstract: We report batch-processed, totally planar, vertical-cavity top surface emitting GaAs/AlGaAs laser devices and arrays. Different size devices are studied experimentally. We measure continuous-wave threshold currents down to 1.7 mA and output powers > 3.7 mW at room temperature. We also discuss interesting characteristics such as differential quantum efficiencies exceeding unity and multi-transverse mode behavior. An array having 64 X 1 individually-accessed elements is characterized and shown to have uniform room-temperature continuous-wave operating characteristics in threshold current approximately equals 2.1 +/- 0.1 mA, wavelength approximately equals 849.4 +/- 0.8 nm, and output power approximately equals 0.5 +/- 0.1 mW.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: This paper examines the transient and steady-state characteristics of several Bussgang-type blind equalization algorithms and the relative performance of the various algorithms is assessed.
Abstract: This paper examines the transient and steady-state characteristics of several Bussgang-type blind equalization algorithms. A combination of computer simulations and analysis is used to assess the relative performance of the various algorithms. The computer simulations involve channel characteristics typical of those found in an urban multipath environment, and they include the effects of frequency offset. The equalizer structures considered in this paper are comprised of a T/2 fractionally-spaced linear finite impulse response filter. The analysis of misadjustment is based on an approximate Gaussian model of the data.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, the receiver performs joint data and channel estimation in an iterative manner, instead of estimating the channel inverse, the receiver computes the maximum likelihood estimate of the channel itself.
Abstract: A new approach to blind equalization is investigated in which the receiver performs joint data and channel estimation in an iterative manner. Hence, instead of estimating the channel inverse, the receiver computes the maximum likelihood estimate of the channel itself. The iterative algorithm involves maximum likelihood sequence estimation (Viterbi decoding) for the data estimation part and least squared estimation for the channel estimation part. A suboptimal algorithm is also proposed that uses a reduced-state trellis instead of the Viterbi algorithm. Simulation results show that the performance obtained by these algorithms is comparable to that of a receiver operating with complete knowledge of the channel.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the authors describe three fundamental methods for attaining full complex modulation. And the mathematics for two of these methods are presented, and signal decomposition in their terms is outlined.
Abstract: Although the action of a spatial light modulator (SLM) is usually restricted to certain locations on the operating curve of the complex plane, NASA is planning to use architectures that allow two continuously variable SLMs to function jointly so as to access the full interior of a closed curve in the complex plane. This paper describes three fundamental methods for attaining full complex modulation. The mathematics for two of these methods is presented, and signal decomposition in their terms is outlined.
TL;DR: In this article, a rigorous diffraction model is used to predict the scatter from a known grating structure, and utilizing this information, the inverse problem of predicting line shape from a measurement of the scatter is performed.
Abstract: Identification of dimensional parameters of an arbitrarily shaped grating using scatter characteristics is presented. A rigorous diffraction model is used to predict the scatter from a known grating structure, and utilizing this information we perform the inverse problem of predicting line shape from a measurement of the scatter.
TL;DR: In this paper, the recording of volume phase transmission gratings in this holographic photopolymer is described and the dependence of holographic properties on exposure conditions, grating characteristics, and processing are discussed.
Abstract: Volume phase holographic gratings provide the high diffraction efficiency often required from holographic optical elements. In order to provide wide angular bandwidth, high index modulation is also required. A new addition to the family of Du Pont holographic photopolymer films has significantly higher index modulation for the grating spacings typical of holographic transmission elements. In this paper, the recording of volume phase transmission gratings in this holographic photopolymer is described. The dependence of holographic properties on exposure conditions, grating characteristics, and processing are discussed. The performance characteristics of holographic optical elements produced in this material are also presented.
TL;DR: Two new filters for image enhancement are developed, extending the early work of the authors, which uses a new nonlinear time dependent partial differential equation and its discretization.
Abstract: Two new filters for image enhancement are developed, extending the early work of the authors. One filter uses a new nonlinear time dependent partial differential equation and its discretization, the second uses a discretization which constrains the backwards heat equation and keeps it variation bounded. The evolution of the initial image as t increases through U(x,y,t) is the filtering process. The processed image is piecewise smooth, nonoscillatory and apparently an accurate reconstruction. The algorithms are fast and easy to program.
TL;DR: The use of the burst derivative measure is proposed as a means to improve the computational efficiency of currently used ISAR algorithms and gives significant improvement in processing speed over the traditional entropy measure now employed.
Abstract: Inverse synthetic aperture radar (ISAR) is an imaging technique which shows real promise in classifying airborne targets inreal-time under all weather conditions. Over the past few years a large body of ISAR data has been collected and considerableeffort has been expended to develop algorithms to form high-resolution images from this data. One important goal of workers inthis field is to develop software that will do the best job of imaging under the widest range of conditions. The success of classifyingtargets using ISAR is predicated upon forming highly focused radar images of these targets. Efforts to develop highly focusedimaging computer software have been challenging, mainly because the imaging depends on and is affected by the motion of thetarget, which in general is not precisely known. Specifically, the target generally has both rotational motion about some axis andtranslational motion as a whole with respect to the radar. The slant-range translational motion kinematic quantities must be firstaccurately estimated from the data and compensated before the image can be focused. Following slant-range motion compensation,the image is further focused by determining and correcting for target rotation. We propose the use of the burst derivative measure
TL;DR: Active and adaptive optics technology has emerged from the laboratory and is being applied to improve the performance of optical imaging and laser systems as mentioned in this paper, among which are high-performance deformable mirrors, new types of wavefront sensors, and more sophisticated wavefront processing algorithms.
Abstract: Active and adaptive optics technology has emerged from the laboratory and is being applied to improve the performance of optical imaging and laser systems. In the last few years, development of both systems and components has accelerated. Many new concepts and devices have appeared, among which are high-performance deformable mirrors, new types of wavefront sensors, and more sophisticated wavefront processing algorithms. Equally important, a better understanding of the system design aspects of adaptive optics has been reached, particularly of the need for optimizing each system according to its application. For example, the dominant requirement in laser systems is to achieve a high Strehl ratio, whereas for ground-based astronomy the availability of guide stars is a major concern. Current developments in adaptive optics for ground-based astronomy include the use of IR wavelengths, partial wavefront compensation using natural guide stars, and the use of laser guide stars to allow all-sky coverage with full compensation at visible wavelengths. While progress to date has been impressive, much work remains to bring this technology into general use.
TL;DR: A new algorithm for the design of phase-only gratings that will shape the relative intensities of the diffracted orders while simultaneously maximizing the light contained in the orders of interest.
Abstract: We present a new algorithm for the design of phase-only gratings. In general, a successful grating design will shape the relative intensities of the diffracted orders while simultaneously maximizing the light contained in the orders of interest. This iterative algorithm achieves both of these goals. Solutions typically have efficiencies of .90 to 1.00 and can be made arbitrarily close to the desired intensity profile. Convergence to a solution is quick for small numbers of orders (about 20) and the performance of the final solution is fairly independent of the starting point.
TL;DR: In this article, the minimum number of actuators for fitting different Zernike orders of wavefront is given, and the arrangement of actuator and the influence function of mirror are discussed in respect of fitting error.
Abstract: Deformable mirror is the key element for adaptive optical wavefront correction. The number of actuators decides the complexity and cost of adaptive optical system. In this paper computer simulations of wavefront error for fitting different Zernike terms by deformable mirror with different number of actuators are presented. The arrangement of actuator and the influence function of mirror are discussed in respect of fitting error. The minimum number of actuators for fitting different Zernike orders of wavefront are given. Some optical experiments of fitting capability have been done with 19 and 37-element deformable mirrors and a Zygo interferometer.
TL;DR: In this article, the optical performance and properties of angle dependent light control glass (LCG) were investigated and it was shown that the microstructure of a specific polymer film sandwiched by a pair of glasses can be explained by diffraction due to a stack of various transmission volume phase gratings.
Abstract: Angle dependent light control glass (LCG) is a new glass that scatters only incident lights from particular angles and transmits incident lights from all other angles. This unique light control function of LCG is caused by the microstructure in the specific polymer film sandwiched by a pair of glasses. The optical performance and properties described in this paper support that the principle of an angle dependent light control function can be explained mainly by diffraction due to the microstructure like a stack of various transmission volume phase gratings.
TL;DR: A framework for combining the essential elements of both the physically-based and probabilistic approaches is proposed, a Kalman filter which incorporates physically- based models as part of the prior and system dynamics and is able to integrate noisy data over time.
Abstract: Models of 2-D and 3-D objects are an essential aspect of computer vision. Physically-based models represent object shape and motion through dynamic differential equations and provide mechanisms for fitting and tracking visual data using simulated forces. Probabilistic models allow the incorporation of prior knowledge about shape and the optimal extraction of information from noisy sensory measurements. In this paper we propose a framework for combining the essential elements of both the physically-based and probabilistic approaches. The combined model is a Kalman filter which incorporates physically-based models as part of the prior and system dynamics and is able to integrate noisy data over time. In particular, through a suitable choice of parameters models can be built which either return to a rest shape when external data are removed or remember shape cues seen previously. The proposed framework shows promise in a number of computer vision applications.
TL;DR: In this article, the integral operator connecting the normal gradient of the scattered field to its boundary values can be represented by an expansion in roughness amplitude that is more rapidly convergent than conventional solution.
Abstract: The integral operator connecting the normal gradient of the scattered field to its boundary values can be represented by an expansion in roughness amplitude that is more rapidly convergent than conventional solution. Each term in the operator series consists of alternating applications of Fourier transforms and multiplications by functions of surface position and wavenumber. The procedure is consequently efficient enough to provide accurate scattering solutions for two-dimensional surfaces (zetz) (x,y) of high roughness amplitude and substantial detail. The appropriate expansion parameter for the scalar problem is the Fresnel roughness, which for a composite random surface scales like the rms slopes times the rms Rayleigh height. For the vector electromagnetic problem an additional, partially independent, parameter arises in the form of squared slope for those roughness scales shorter than the radiation wavelength.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this paper, a range-gated underwater imaging system is described that utilizes a frequency doubled, Q- switched Nd:YAG 30 Hz laser source for illumination and a fast gated microchannel plate intensified CCD array camera for detection.
Abstract: A range-gated underwater imaging system is described that utilizes a frequency doubled, Q- switched Nd:YAG 30 Hz laser source for illumination and a fast-gated microchannel plate intensified CCD array camera for detection. Laser pulse widths of 7 ns are timed relative to comparable camera gates with subnanosecond jitter. Results for a test bed system obtained in a 4 X 4 X 40 ft water tank with various targets are presented. Water quality was varied with the addition of progressive concentrations of Maalox as scattering agent, and monitored with a home-built laser transmissometer. The 1/4 in., high contrast target lines were able to be resolved at ranges exceeding four attenuation lengths. A simple analytical model for image signal-to-noise ratios is presented and a straightforward polarization discrimination scheme suggested for contrast enhancement. Polarization optics were incorporated into the range-gated test bed system and results obtained for targets of varying characteristic depolarization. In all but a few cases where target and background depolarizations were similar, the signal to noise is enhanced in spite of rejection of orthogonal polarization signal. Issues regarding the evolution of the test bed system to field operation are discussed and significant progress in the development of appropriate miniaturized and ruggedized components is presented
TL;DR: In this paper, the nonresonant (pi) -electronic component of (gamma) (- 3(omega) ;(OMEGA) ; (OMEGA),(omeGA),(OMEga),(OMEG),(OMG), (OMEG ),(OMEGI), (OMG ), (OMEGI), (Gamma) (pi), (gammma) xxxx), is calculated for all-trans, linear symmetric cyanine, and streptocyanine cations with no double-single bond-length altern
Abstract: The nonresonant (pi) -electronic component of (gamma) (- 3(omega) ;(omega) ,(omega) ,(omega) ), (gamma) (pi) , is calculated for all-trans, linear symmetric cyanine, and streptocyanine cations with no double-single bond-length alternation, and for cyanine cations with asymmetric geometries resulting from the artificial imposition of double-single bond-length alternation. These (gamma) (pi) are compared with those previously calculated for all-trans linear polyenes with double-single bond-length alternation, and for a new set calculated with geometries resulting from the artificial imposition of no double-single bond-length alternation. Bond-length alternation is found to dramatically affect (gamma) (pi) for the linear cyanines: the (gamma) (pi) for the symmetric cyanines are calculated to be negative; the (gamma) (pi) for the asymmetric cyanines change from negative to positive with increasing chain length. The (gamma) (pi) for the linear polyenes are always positive regardless of the extent of bond-length alternation; the (gamma) (pi) for the linear polyenes increase with decreasing bond-length alternation. The (gamma) (pi) for the symmetric linear cyanines increase more rapidly with the number of (pi) -electrons than the (gamma) (pi) for the linear polyenes: (gamma) (pi) (symmetric cyanines) varies as N(pi -e)8 and (gamma) (pi) (linear polyenes) varies as N(pi -e)4, where Npi-e equals 4, 6, 8, 10, 12. The (gamma xxxx component along the chain axis is the most dominant one of (gamma) (pi) for all linear molecules studied. The salient 1(pi) (pi) * states and the important terms in the sum-over-states expression that define (gamma) xxxx, and hence (gamma) (pi) , are identified for the molecules. The dependence of (gamma) (pi) and (beta) (pi) on the geometric asymmetry of a pentamethine cyanine cation is investigated. The polymethines in general, and the cyanines in particular, comprise a very interesting class of nonlinear optical, (pi) -electron molecules that merit further experimental study.
TL;DR: Microrelief patterns with characteristic dimensions as small as the wavelength of light can now be mass reproduced to form high-quality and low-cost optical components, allowing optics designers to create innovative optical components that promise to solve key problems in optical sensors optical communication channels and optical processors.
Abstract: Through advances in semiconductor miniaturization technology, microrelief patterns, withcharacteristic dimensions as small as the wavelength of light, can now be mass reproducedto form high-quality and low-cost optical components. In a unique example of technologytransfer, from electronics to optics, this capability is allowing optics designers to createinnovative optical components that promise to solve key problems in optical sensors,optical communication channels, and optical processors.1. INTRODUCTION Many of the current micro structures in optics are based on binary optics technology.This is an inherently diffractive optics technology that uses computer-generated designs ofmicroscopic relief patterns and electronic circuit etching technology to create novel opticaldevices and to provide design freedom and new materials choices for conventionalrefractive optical elements. Over the past ten to twelve years we in the holographic opticscommunity have learned to produce diffractive and mixed refractive-diffractive devices thatare highly efficient and of high enough quality to be used in cameras and in medicalapplications. These devices are fabricated by methods compatible with current lithographicand integrated circuit techniques.In the early seventies, the Defense Advanced Research Projects Agency (DARPA) ,
TL;DR: Analog fiber-optic links using an integrated-optical intensity modulator have been demonstrated and analyzed as mentioned in this paper, and the link performance has been shown to have a simple dependence upon a few link design parameters.
Abstract: Analog fiber-optic links using an integrated-optical intensity modulator have been demonstrated and analyzed. Experimental links operate at frequencies from 40 MHz to 22 GHz with electrical gain up to 11 dB, noise figure as low as 6 dB, and intermodulation-free dynamic range of up to 113 dB-Hz2/3. The gain, noise figure, and dynamic range are shown to have a simple dependence upon a few link design parameters. Other factors affecting link performance, such as stimulated Brillouin scattering, interferometric intensity noise, modulator linearization, and addition of an optical amplifier, are also discussed briefly.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
TL;DR: In this article, the formation and selected properties of composites made from DMP-128 transmission holograms and the nematic liquid crystal E7 were analyzed by polarizing microscopy, refractive index measurements and differential scanning calorimetry.
Abstract: We describe the formation and selected properties of composites made from DMP-128 transmission holograms and the nematic liquid crystal E7. Analysis of the liquid crystal structure in the composites by polarizing microscopy, refractive index measurements, and differential scanning calorimetry produced two primary observations. (1) Treatment of the interior surface of the porous holograms controls the nature of the liquid crystal alignment; both planar and homeotropic alignment is possible for the E7 composites. (2) Incorporation of E7 into DMP composites significantly reduces its degree of order compared to that for a standard nematic cell.
TL;DR: A Tropospheric Emission Spectrometer for the Earth Observing System (EOS) series of polar-orbiting platforms is described, aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere.
Abstract: A Tropospheric Emission Spectrometer (TES) for the Earth Observing System (EOS) series of polar-orbiting platforms is described. TES is aimed at studying tropospheric chemistry, in particular, the exchange of gases between the surface and the atmosphere, urban and regional pollution, acid rain precursors, sources and sinks of greenhouse gases, and the interchange of gases between the troposphere and the stratosphere. TES is a high-resolution (0.025/cm) infrared Fourier transform spectrometer operating in the passive thermal-emission mode in a very wide spectral range (600 to 4350/cm; 2.3 to 16.7 microns). TES has 32 spatial pixels in each of four optically conjugated linear detector arrays, each optimized for a different spectral region.