This PDF file contains the editorial “Editorial: 2004 in Review” for OE Vol. 44 Issue 02

A tunable filter that can be applied for dispersion compensation, a multiwavelength laser source, or a channel transmitter/attenuator is proposed. Channel spacing and dispersion can be controlled simultaneously by using a motorized polarization differential delay line and a variable coupler in the loop mirror. Due to its periodic characteristic, chromatic dispersion of multiple channels can be compensated all at once.

For optical clock recovery of nonreturn-to-zero (NRZ) signals more than 40 Gb/s, we propose and experimentally demonstrate a simple clock recovery scheme using beat processing. Through the proposed scheme, we square the adjustment range of the variable optical attenuator (VOA) and achieved an enhanced clock-to-noise ratio (CNR) of more than 15 dB in the experiment, compared to a system without the proposed scheme.

A 10-Gbit/s wavelength-division-multiplexing (WDM) transport system over a 50-km single-mode fiber (SMF) transport based on vertical cavity surface emitting lasers (VCSELs) and a semiconductor optical amplifier (SOA) with an external light injection technique is proposed and demonstrated. Improved bit error rate (BER) performance is observed under direct modulation of four channels at 2.5 Gbit/s, attributed to the SOA light injection technique to reduce the SOA-induced distortion and crosstalk.

Fiber optic interferometric refractometers usually possess large temperature sensitivities, especially those based on individual long-period gratings. This work introduces a compound-cavity Michelson interferometer that uses mode coupling in a long-period grating to establish the two optical paths in a single fiber, and therefore presents a compact sensor for in vivo refractive index measurement. Successful operation of the athermal refractometer was demonstrated experimentally by comparing its phase shift due to temperature-dependent changes of the refractive index of the analyte with refractive index readings from a temperature-controlled Abbe refractometer.

We present an improved method that is suitable for gradient-threshold edge detectors. The method takes into account the basic characteristics of the human visual system and masks the gradient image with the luminance and the activity of local image before edge labeling. An implementation of this method on a Canny detector is described as an example. The results show that the edge images obtained by our algorithm are more consistent with the perceptive edge images.

A split Monte Carlo algorithm based on Phong's radiation model for the calculation of the impulse response on infrared wireless indoor channels with various reflecting property is presented. It allows evaluation of not only Lambertian-diffuse but also direction-diffuse reflections. The numerical burden can be dramatically reduced with nearly geometric growth in the number of rays compared to classical deterministic algorithm for exponential ray growths.

This paper mainly discusses the validity and the reliability of the stray light calculation code using the Monte Carlo method in an optical system. As a new method, the symmetrical test of radiation in two-dimensional media (STRTDM) is presented to verify the characteristics of pseudorandom numbers. The method can provide great flexibility and simplicity under various calculation conditions through iteratively comparing the performance of the pseudorandom number generators (PNGs) until a sufficiently good PNG is obtained. After a series of tests have been performed—including tests for the characteristics of a PNG, for the reliability of probability models, and for the summation reciprocity relationships of the radiative exchange factor—the results show the reliability of the stray light calculation code in this paper. Moreover, the Monte Carlo computer code is verified by comparing its predictions with previously published results for optical geometries similar to ours.

Diffractive wavefront control with programmable optically efficient modulo gratings has been successfully demonstrated as a means of compensating large optical aberrations and steering an outgoing beam over small angles without mechanical motion. This work builds on past work to demonstrate the integrated performance of a programmable diffractive element of large pixel count with a telescope system. More specifically, a liquid-crystal-based spatial light modulator is used as a reconfigurable diffractive optical element in a telescope system to compensate for large aberrations associated with variations in object range and field angle within the telescope's field of regard. The telescope consists of a conventional primary mirror that gimbals relative to the other components of the system and a programmable diffractive optic that compensates for more than 40 waves of aberration associated with defocus and off-axis aberrations. In this setup, aberration compensation via the programmable diffractive optic allows the object range to be varied by 160 times the depth of focus and increases the diffraction-limited field of regard by a factor of 70 while maintaining near-diffraction-limited performance.

The development efforts in two-wavelength contouring methods of holographic interferometry are mainly along one line: The lateral shift between two images that are recorded at two different wavelengths but are both reconstructed at one of them is to be eliminated as automatically as possible. The present paper takes an opposite approach. A manual elimination process is intentionally maintained, and it is supported by precise visual monitoring. The advantage of this approach is threefold. First, the final accuracy of the elimination is visually displayed and controlled with interferometric precision. Second, exaggerated tilt compensation can result in the subtraction of an extra compensation fringe system from the real one to be measured. In this way, object positioning inaccuracies can be compensated and in addition the upper limit of the measuring range can be extended. In our experiments, a threefold measuring range extension was demonstrated. Third, the intensities of the two reconstructed images can be adjusted to each other if needed. Tilt compensation and intensity adjustment are especially advantageous features at the realization of the comparative two-wavelength contouring by difference holographic interferometry.

A method to enlarge the dynamic range of a CCD-based laser beam profiler is presented. The method is based on extended-image-range techniques. The algorithm that generates the extended-irradiance-range image is described in detail. An equivalent dynamic range and number of bits are defined and computed for the new profiling system. To test the method, experimental measurements of the principal widths of the output beam from a single-mode optical fiber have been made, as well as the Fraunhofer diffraction pattern of a 200-µm pinhole back-illuminated by a HeNe laser.

A planar encoder using conjugate optics is proposed for sensing the 2-D displacement of a 2-D grating. A Doppler frequency shift of diffracted light is generated when the grating moves. The optical conjugate path can compensate for the error arising from the relative tilt between the optical head and the scale (head-to-scale tilt). Additionally, the optical head is easily integrated, having high tolerance in component-to-component placement. The 2-D displacement system with the 2-D grating, which has period of 1.6 µm in both the X and Y directions, provides a signal period of 0.4 µm by using a double-diffraction configuration. This system and associated electronics provide interpolation with a factor of 400, corresponding to a measurement resolution of 1 nm.

This paper presents a methodology to obtain polarization profiles using a commercial off-the-shelf (COTS) digital camera. It contains calibration techniques to ensure robust and accurate determination of the Stokes parameters and the system polarization state. It calculates the Stokes parameters for each scene pixel along with the degree of polarization, azimuth, and ellipticity angles for each of the RGB channels. A detailed calculation shows that the quasimonochromatic approximation for the wavelength dependence of the quarterwave plate can be extended to include the broadband RGB channels. A simple and inexpensive camera calibration converts RGB values to optical density and then to relative intensity values. An analysis is presented for the wavelength-dependent response of the tuned zero-order quartz quarterwave retarder, the broadband RGB channels, and the fourth Stokes parameter. The noise characteristics of the digital camera are analyzed along with a detailed calibration of the imagery for target characterization applications. An extensive validation process, using white light, compares calculated theoretical results with the empirical results from the COTS camera. A RGB pseudocoloring scheme, related to the Poincaré sphere, is introduced for the visualization of polarization parameters of daylight scenes.

We present a novel laser ranging system that offers improved accuracy and low-cost implementations for short to medium range target distance and velocity measurement. This is accomplished through the emission of an eye-safe amplitude modulated laser beam, whose echo return is processed with a phase-computing discrete Fourier transform (DFT). The data for the DFT are collected directly from the received signal through equivalent time sampling, and the automatic gain control (AGC) function is moved to that part of the system where its varying signal propagation time will not impact measurement accuracy. All emission and data collection signals are derived directly from a single crystal oscillator, which establishes the system's accuracy. The system is also capable of resolving the distance/velocity ambiguity problem inherent in conventional hetero/homodyne laser ranging systems, and, lastly, digital data can be transmitted and received concurrently with the distance measurement process.

Color coding has been used for 3-D shape measurement in many recently developed fringe projection techniques. Use of color allows for more information to be coded in the same number of patterns as compared to the black-and-white techniques. However, one major problem of using color is that the appearance of the color fringe patterns projected onto the object can be affected by the color of the object surface itself. Thus, correctly decoding the fringe patterns can be difficult and sometimes even impossible. We describe a color-coded binary fringe projection technique that solves this problem. The use of an adaptive threshold scheme enables the extraction of the 3-D information and texture of an object without being affected by the color of the object surface. The development of a color gray-code concept, which is an extension of the gray-code technique, further reduces decoding errors. In addition, this technique can be used to measure objects with discontinuous features. The system has small digitizing errors and its measurement accuracy is hardly affected by system noise and nonlinearity errors. The system setup, color pattern design, shape reconstruction, and experimental results are presented

Optically thin palladium films evaporated on silicon substrates are investigated following exposure to low concentrations of hydrogen gas in nitrogen using spectroscopic ellipsometry. Changes in the parameters tan Ψ and cos Δ are observed for concentrations as low as 0.01% hydrogen in nitrogen. A nonlinear behavior of the change in the ellipsometry parameters as a function of hydrogen concentration is demonstrated, with saturation occurring at a flow of 0.05% hydrogen in nitrogen.

A technique is described for modifying the spectral profile of a Fabry-Perot etalon by introducing a spatial variation to the etalon thickness and reflectivity. The viability of the technique is demonstrated by grinding and polishing a solid lithium niobate etalon to give a controlled thickness variation. A flat-topped transmission profile is generated from the measured thickness map, and further modification of the profile is predicted by introducing customized variations in thickness and reflectivity of the etalon mirrors

An optical see-through head-mounted display (HMD) system integrating a miniature camera that is aligned with the user's pupil is developed and tested. Such an HMD system has a potential value in many augmented reality applications, in which registration of the virtual display to the real scene is one of the critical aspects. The camera alignment to the user's pupil results in a simple yet accurate calibration and a low registration error across a wide range of depth. In reality, a small camera-eye misalignment may still occur in such a system due to the inevitable variations of HMD wearing position with respect to the eye. The effects of such errors are measured. Calculation further shows that the registration error as a function of viewing distance behaves nearly the same for different virtual image distances, except for a shift. The impact of prismatic effect of the display lens on registration is also discussed.

Moiré fringes appearing in contact-type three-dimensional imaging systems cause serious image quality deterioration. The fringes are inevitable because the systems require overlapping a viewing-zone-forming optical plate on a display panel. An analysis shows that the visual effects of the fringes can be minimized by finding a proper overlapping angle between the panel and the plate. This angle imposes that pixel cell in full-parallax imaging systems should have the shape of either rhombus or parallelogram with a specific vertex angle. The pixel cell with the shape of the rhombus or parallelogram is implemented by approximating the boundaries of each pixel cell by staircase lines drawn along sides of the pixel. The slopes of the lines are determined by the ratio of the pixel numbers in the vertical and horizontal directions. This method allows creating pixel cells with a desired vertex angle for minimizing the moiré fringes, especially in full-parallax imaging systems.

When a twin laser emits the mode fields in coherent form, a Y waveguide can be used to mix and focus the twin signals in the longitudinal axis of a fiber core. In best conditions of coupling, both modal fields are assumed to mix coherently in the waveguide junction. A general expression is derived for the coupling coefficient as a function of the longitudinal displacement between components and misalignments of vertical and angular errors. We show how the Y waveguide avoids the drop in coupling efficiency caused by the separation between main emitters and the longitudinal axis of the fiber, and calculate the coupling factors between each main signal and the signal transmitted through the furthest Y waveguide branch to estimate the order of magnitude of possible losses. The coupling efficiency between the TE fundamental mode field and one branch is compared with the expression obtained using the Gaussian approximation. The intensity transmitted by the whole system using a coupled twin-mode solution is analyzed, taking into account the general coupling coefficients between main stripe outputs and branches.

A tunable electro-optically Q-switched rf-excited partial Z-fold CO₂ waveguide laser with two channels has been designed. Q-switched pulses were obtained from the partial Z-fold channel. The peak power is 730 W, and the pulse width is 150 ns. Cw laser output was obtained from the other channel, which can be tuned by a grating. A stable pulse heterodyne waveform and its Fourier transform (frequency spectrum) were also observed.

This study demonstrates that the cladding modes of a tilted superstructure fiber grating can be coupled back to the core mode to create induced channels by acousto-optic interactions when the acoustic wave traveling along the fiber axis vibrates the fiber. This phenomenon is based on the acoustic wave vector matching the difference between the core mode and the cladding mode wave vector. Acoustic power levels can be used to control the reflectivity and number of the induced wavelength channels. Moreover, the wavelength location of the induced channel can be tuned by varying the acoustic wave frequency. Thus, the proposed device may provide a switchable multiwavelength comb filter for applications in wavelength-division multiplexing systems, fiber lasers, or fiber sensors.

The implementation of optimum Hamming apodized acousto-optic 2×2 add/drop multiplexers using SiO₂ film-loaded surface acoustic waveguides with angular offset to a Ti:LiNbO₃ waveguide is presented. The sidelobe suppression and 3-dB optical bandwidth for a 20-mm interaction length and 32-mW rf drive power are 19 dB and 1.5 nm, respectively. A tuning rate of –8.1 nm/MHz and fiber-to-fiber insertion loss <7.0 dB is obtained.

We report our theoretical analysis on polarization mode dispersion (PMD) tolerance of the return-to-zero transmission system under error-free [bit error rate (BER)≤ 10^–12] conditions. The results show that the tolerable PMD cannot be further enhanced by increasing the receiver power margin when forward error correction is used. The investigation also reveals that optimal receiver bandwidth for minimum BER should be increased accordingly when the accumulated PMD is increased. By designing the receiving filter with adaptive bandwidth, the acceptable average differential group delay can be improved by up to 2% of the bit interval.

New measurement techniques and methods for characterizing the quality of optical fibers are presented. The fibers are to be used in a single-fiber-fed heterodyne laser interferometer with nanometer uncertainty. The polarization-mixing properties of several different polarization-maintaining fiber types, as well as the effects of fiber lengths on high-precision length measurements, is investigated for the first time. Mixing ratio and polarization orthogonality were measured using three different methods. The measured mixing ratios varied between 1:100 and 1:1650 (intensity). Also the influence of the fiber assembly on the polarization-mixing properties is shown.

For beam delivery in a single-fiber-fed heterodyne laser interferometer with nanometer uncertainty, the use of polarization-maintaining (PM) fibers is investigated. The PM properties of the light emerging from the fiber determine the achievable measurement accuracy. Measurements of the polarization-mixing properties of several different PM-fiber types as well as a range of fiber lengths were described in part I of this paper. In this part, a model and analysis of the fiber are presented. By means of the analytical model, a quick selection method is given, which can also be used to precisely align the fiber with respect to the other optical components of the interferometer. The presented model, based on Jones matrices, allows the investigation of local and global disturbances within the fiber and their location. As in part I, the dominant effect of the connector in the fiber assembly is shown. The effects of imperfections in fiber material are shown for longer fibers; they change the dominating connector effect slightly.

We demonstrate an unrepeated transmission of 16×42.8 Gb/s over 200 km of a standard single-mode fiber (SMF) using a commercially available electroabsorption modulator (EAM). In an optical link, a distributed fiber Raman amplifier, a remote pumped optical amplifier, an optical booster amplifier, and an optical preamplifier are used for signal amplification. After transmission of 200 km, Q-values of the 16 channels range from 11.5 to 12.3 dB. The experimental result reveals that the EAM can be used for STM-256 (OC-768)-based long as well as short reach applications.

Based on formulas presented, optimization design is performed and the effects of manufacturing tolerances on transmission characteristics are analyzed for a polymer microring resonant wavelength multiplexer around the central wavelength of 1.550918 µm with wavelength spacing 1.6 nm. Modeling results show that the insertion loss is less than 0.55 dB and crosstalk is less than –21 dB for each of eight vertical output channels of the designed device without tolerances. Some manufacturing tolerances result in a shift of the transmission spectrum and lead to increases of the inserted loss and crosstalk over the design case without tolerances

The implementation of a low-loss demultiplexer with a KRS-5 grism structure for a dense wavelength division demultiplexing (DWDDM) system in fiber communication is carried out. The system has 16 channels with wavelength spacing of 0.8 nm in the C-band wavelength region. This device is successfully fabricated by a precise plunge-cut diamond-turning technology. Numerical calculations and measurements indicate that this DWDDM is polarization independent and has higher optical efficiency and signal to noise ratio (SNR).

The regular net of optical vortices can be generated by three plane wave interference. Such regular vortices are used in a new kind of interferometry—optical vortex interferometry. In this work, the experimental method for topological charge determination of optical vortices in a regular net is presented. This allows for unique phase reconstruction in optical vortex interferometry and solves what is known in interferometry as the phase unwrapping problem.

Full characterization of the surface strain requires the measurement of six displacement gradient components of the surface strain tensor. The out-of-plane displacement gradient component may be directly measured using the full-field speckle interferometry technique of shearography, but to fully characterize the surface strain using shearography, a minimum of three illumination, or viewing, directions are required. The image processing technique of digital speckle photography (DSP) is sensitive to in-plane displacement for normal collinear illumination and viewing, with the displacement gradient components obtained by differentiation. A combination of shearography and digital speckle photography is used to perform full characterization of the surface strain using a single illumination and viewing direction. The increase in complexity compared with a standard single-channel shearography system lies predominantly in the additional image processing requirements. Digital speckle photography image processing is performed using the optical flow field technique and the advantages of this technique compared with correlation are discussed. The design of the instrument is described and full surface strain measurements made with the system are presented.

This paper deals with the problem of very accurate relative attitude determination between distant spacecraft, performed by laser interferometric techniques. The presented method, based on wavefront splitting interferometry with flat reflectors, is intended to be a possible alternative approach to the more classical one utilizing a telescope plus quadrant photodiode detector. Depending on the instrument configuration and size and on available detector technology, accuracy in the submilliarcsecond range appears achievable. The paper provides an introduction on flat-mirror interferometry, a presentation on basic relationships and fringe formation, and consideration of performance in attitude reconstruction.

The infrared reflectance and emittance of a double layer of silicon and silicon dioxide have been investigated by optical multilayer calculations and spectral and wavelength-integrated measurements. Low emittance in the interval 0.2 to 0.4 can be obtained simultaneously in both thermal atmospheric windows: 3 to 5 and 8 to 13 µm. These results are relevant for IR signature control. The sample consisted of a 0.9-µm Si and a 2.45-µm SiO₂ layer on a Si wafer. The layers were grown by standard microelectronic chemical vapor deposition techniques. The key mechanism for lowering the emittance is the interaction between the SiO₂ molecular reflectance band, around 9 µm, and interference effects in the double layer. Interference gives one peak in the 3- to 5-µm window, and a widening and strengthening of the SiO₂ molecular reflectance band in the 8- to 13-µm window. The calculated spectra are in very good agreement with measured near-normal incidence reflectance spectra in the range 2.7 to 12.5 µm. The emittance of the samples heated to 61°C was determined in the atmospheric windows using two heat cameras filtered for the respective intervals and equipped with polarizers. Emittance values for the sample in the two windows and the two main polarizations were determined as a function of emission angle from 10 to 60 deg. Qualitative agreement with values calculated from tabulated optical constants was obtained.

We propose a novel decision fusion algorithm for target tracking in forward-looking infrared (FLIR) image sequences recorded from an airborne platform. The algorithm allows the fusion of complementary ego-motion compensation and tracking algorithms to estimate the position of the target in the current frame among a sequence of frames of FLIR imagery. We identified three modes that contribute to the failure of the tracking system: (1) the sensor ego-motion failure mode, which causes the movement of the target beyond the operational limits of the tracking stage; (2) the tracking failure mode, which occurs when the tracking algorithm fails to determine the correct location of the target in the new frame; (3) the reference-image distortion failure mode, which happens when the reference image accumulates walkoff error, especially when the target is changing in size, shape, or orientation from frame to frame. The strategy in our design is to prevent these failure modes from producing tracking failures. The overall performance of the algorithm is guaranteed to be much better than any individual tracking algorithm used in the fusion. One important aspect of the proposed algorithm is its recoverability: the ability to recover following a failure at a certain frame. The experiments performed on Army Missile Command AMCOM FLIR data set verify the robustness of the algorithm.

There is a tradeoff between effective and computational costs in traditional change detection methods. Reducing the computational cost of the processing time results in loss of quality of detection results. We propose a new change detection method based on the temporal difference principle. The new method combines the connected component labeling, closing operation of image morphology, and human structure analysis to remove shading and noise in consecutive frames. A closed object boundary and region can be extracted with only a small additional cost in processing times. Additionally, this new method recovers the disadvantages of traditional temporal difference methods. Comparative results, in terms of computational complexity, completeness of the object and the object's outline, robustness against noise and shadow, with currently popular methods and the proposed method are also displayed. The experimental results show that the proposed method is robust in varied illuminations and effective in several predefined environments for change detection.

Divergent projection refers to fan-beam or cone-beam projection originating from a point source, which is commonly seen in x-ray imaging. Conventionally, the divergent projection calculation is carried out using a ray model, in which each detector pixel (cell) receives radiations emanating from a point source, in a form of straight-line ray. The finite dimension of the detector pixel develops a zero-width ray into a nonzero-width strip, with its cross section assuming the effective aperture of a detector pixel facet. In the pursuit of accuracy, we portray the divergent projection from the point source radiation on a detector cell by a pyramidal element (pyrel), which is formed by a pyramidal base (detector pixel facet) and an apex (point source). A pyrel intersects the object and circumscribes a trapezoidal zone for fan-beam projection (a frustum volume for cone-beam projection), wherein the object voxels are accumulated (appropriately weighted) to produce the detector cell's signal. In addition to the forward divergent projection calculation, the pyrel model can be used for iterative object reconstruction by repeating the backprojection and reprojection. Since the pyrel model portrays more naturally the divergent projection geometry, it maximizes the calculation accuracy, though at the cost of more computations. This model may be rewarding in certain situations: (1) when the detector resolution is unacceptably low, (2) when the projection data set is severely incomplete (for example, the number of projections <100), and (3) when the projection-beam angle is too large (say, >40 deg). Simulations on an iterative fan-beam tomographic reconstruction, using the pyrel model, the ray model, and the voxel-splatting model, are demonstrated.

We evaluate a preprocessing method for image compression artifact reduction based on nonlinear diffusion filtering that we proposed earlier. The method consists of using edge-adaptive diffusion processes before the discrete cosine transform (DCT)-JPEG compression. By using a simple measure for artifact reduction, we show that considerable artifact reduction is achieved with preprocessing at the same bit rate as, and with no greater error than, the original compression. We also show that preprocessing helps to preserve the true contours for image processing applications. An automatic parameter selection for the preprocessing is also proposed, considering the edge histogram of the image and depending on the compression ratio. We test the method for visual quality with extensive subjective measurements. We show that, depending on the image content, preprocessing can significantly improve the visual quality at low bit rates.

We present a new approach to optically calibrate a multispectral imaging system based on interference filters. Such a system typically suffers from some blurring of its channel images. Because the effectiveness of spectrum reconstruction depends heavily on the quality of the acquired channel images, and because this blurring negatively affects them, a method for deblurring and denoising them is required. The blur is modeled as a uniform intensity distribution within a circular disk. It allows us to characterize, quantitatively, the degradation for each channel image. In terms of global reduction of the blur, it consists of the choice of the best channel for the focus adjustment according to minimal corrections applied to the other channels. Then, for a given acquisition, the restoration can be performed with the computed parameters using adapted Wiener filtering. This process of optical calibration is evaluated on real images and shows large improvements, especially when the scene is detailed.

The polarimetric characterization of a beam reflected onto a dielectric surface provides information about the orientation of this surface. From this principle, we present an original method for passive 3-D reconstruction of unknown objects. A specific vision system has been designed that enables polarization image acquisition and processing. The 3-D reconstruction is achieved by an integration process whose initialization data are provided in an original way by a cooperative edge-based stereo vision algorithm. Results obtained from real scenes are presented, which show off the reliability of our method applied to objects without any available a priori information as well as for flat or curved surfaces.

We present a competitive learning vector quantization with evolution strategies for image compression. This technique embeds evolution strategies (ES) into the standard competitive learning vector quantization algorithm (CLVQ). After each iteration during the CLVQ training process, the so-far generated codebook is adjusted by the embedded ES through its recombination, mutation, and selection process. The proposed algorithm can efficiently overcome CLVQ's problems of under-utilization of neurons and initial codebook dependency. The embedding of ES greatly increases the algorithm's capability to avoid local minimums, leading to a global optimization. Experimental results demonstrate that it can obtain significant improvement over CLVQ and other comparable algorithms in image compression applications, especially when it involves larger codebooks.

Optical-electronic leveling devices using a staff with bar codes are discussed. The reading of the staff is taken along its longitudinal axis; the distance to the staff and its vertical position are determined by the readings of a translational transducer connected to the optical system during its focusing on the bars of the staff. The height is determined according to coded signals of the image of the bars transferred into an array of photoelectric cells in the instrument and processed by a microprocessor to the height values. Three main types of image processing are used in various types of digital levels: a correlation method, a geometric method, and a phase method. The correlation functions of measuring and reference codes in the electronic level are calculated in this paper, showing possible errors of height determination. The information obtained during the measurement shows the relationship between the information entropy received from different values of readings from the staff. A new digital level design is proposed, simplifying the design of the instrument and the staff as well. The principal correlation and error determination equations are given, and diagrams of the new design are included.

This paper presents a distortion-tolerant 3-D volume object recognition technique. Volumetric information on 3-D objects is reconstructed by x-ray imaging. We introduce 3-D feature extraction, volume matching, and statistical significance testing for the 3-D object recognition. The 3D Gabor-based wavelets extract salient features from 3-D volume objects and represent them in the 3-D spatial-frequency domain. Gabor coefficients constitute feature vectors that are invariant to translation, rotation, and distortion. Distortion-tolerant volume matching is performed by a modified 3-D dynamic link association (DLA). The DLA is composed of two stages: rigid motion of a 3-D graph, and elastic deformation of the graph. Our 3-D DLA presents a simple and straightforward solution for a 3-D volume matching task. Finally, significance testing decides the class of input objects in a statistical manner. Experiment and simulation results are presented for five classes of volume objects. We test three classes of synthetic data (pyramid, hemisphere, and cone) and two classes of experimental data (short screw and long screw). The recognition performance is analyzed in terms of the mean absolute error between references and input volume objects. We also confirm the robustness of the recognition algorithm by varying system parameters.

Lord Rayleigh derived the degree of polarization for singular molecular scattering phenomena in the atmosphere as a function of the relative angular orientations of the source, scattering center, and observer. This paper extends the Rayleigh model by giving the azimuth angle for the linearly polarized scattered radiation detected by the observer. Together these two parameters give a complete Stokes vector characterization of Rayleigh scattering in the earth-horizon coordinate system. An experimental validation confirms the analytical results. The validation methodology uses a polarization axis finder attached to a commercial off-the-shelf digital camera. Each image supplies enough information to calculate the skylight polarization azimuth angle in real time. The equation for the skylight polarization azimuth angle is used to create a pictorial representation of the polarized sky by using colors to represent azimuth angles. A color scheme is used to display the degree of polarization and the polarization azimuth angle of a vehicle at several different times in daylight. An analysis of the reflected polarized light from the vehicle is included.

The contrast of shadow moiré at high-order Talbot distances is studied. An exact solution for the contrast of shadow moiré fringes is developed from the diffraction phenomenon and its validity is corroborated experimentally. The result is combined with an additional effect from the finite aperture of the camera to propose a complete expression for the contrast of shadow moiré fringes. The results can guide the design of shadow moiré configurations with high-order Talbot distances for high-sensitivity measurements.

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