Effect Of Specular Reflection Research Articles

Estimation of chlorophyll concentration in lakes and inland seas with a field spectroradiometer above the water surface.

The estimation of chlorophyll concentration in the water by use of a field spectroradiometer above the water surface is necessary for the removal of the effect of specular reflection at the water surface. The amount of specular reflection from the water surface was assessed on the basis of the spectral signature data that was measured above and below the water surface. Furthermore, a method to remove the effect of specular reflection from spectral signature data that was measured above water surface was proposed. Finally, chlorophyll-a concentration was estimated accurately from the spectral signature measured by field spectroradiometer above water surface with the proposed surface reflection model.

The Effect of the Urban Street Canyon on the Noise from Low Flying Aircraft

The effect of urban streets on the noise from a low-flying aircraft has been investigated. The study first involved the development of a prediction method based on geometrical acoustics with the assumption of specular reflections. The effect of a variety of street configurations on the transmission gain was investigated and analysed in terms of changes in street geometry. The relative Effective Perceived Noise Level was also predicted. The predictions show that for specular reflections the relative Effective Perceived Noise Level increases in proportion to the ratio of building height to flying altitude, however, changing the street width has only a minor effect. The effect of mixed specular and diffuse reflections was investigated using a commercial acoustical modelling package and it was shown that although the effect on the transmission gain was small, the scattering of sound energy out of the street channel resulted in a decrease in the value of the relative Effective Perceived Noise Level with the ratio of building height to flying altitude resulting in a value of the relative Effective Perceived Noise Level which was negative for most street configurations examined. It can be concluded that although simple specular models can predict the transmission gain with reasonable accuracy, more complex models involving the effects of diffuse reflections are required for noise units involving integration over time.

Simple Blurry Reflections with Environment Maps

We present a technique which uses existing OpenGL capabilities to approximate the effect of blurry specular reflections and indirect diffuse illumination. It makes use of environment maps, mipmapping with level of detail control, and possibly texture borders. The method is extremely simple to implement, in some cases requiring just a single additional OpenGL statement.

Band-structure calculations of specular reflection in spin valves

Band structure calculations are carried out on three types of spin-valve structures: (1) simple spin valves, (2) dual spin valves, and (3) spin valves with a synthetic antiferromagnet. The effect of specular reflection is studied by comparing the transport properties of spin valves with resistive metallic and insulating layers at the outer boundaries. In the spin valve with a synthetic antiferromagnet, an insulating layer needs to be inserted inside the reference layer to achieve similar enhancement to the giant magnetoresistance as the other two types of spin valves with insulating outer boundaries. Results are analyzed in terms of s–d scattering in the different spin channels with different boundary conditions.

FEASIBILITY OF DETECTING SOIL NITRATE CONTENT USING A MID–INFRARED TECHNIQUE

The long–range goal of this study was to develop a portable, soil nitrate sensor to determine soil nitrate content in–situ. The immediate objective of this study was to develop a rapid technique to determine soil nitrate content using diffuse reflectance spectroscopy in the mid–infrared (MIR) range. A Fourier Transform Infrared (FTIR) spectrophotometer was used to determine the MIR response of various concentrations of calcium nitrate solution in water. The results clearly showed the existence of a strong nitrate absorption peak at 7194 nm (1390 cm –1 ). For KBr–diluted soil samples, the ratio of the area under the nitrate absorbance peak (1360–1390 cm –1 ) to the water absorbance peak (1640–1660 cm –1 ) was proportional to nitrate concentration. Mid–infrared diffuse reflectance spectroscopy detected soil nitrate content at low concentrations in KBr–diluted soil samples. However, when undiluted soil samples containing varying amounts of nitrate content were tested in the MIR range, it was necessary to further condition the data with noise filtering techniques. Three noise removal techniques were compared to improve the spectral quality: (1) the Savitzky and Golay, (2) FFT filtering, and (3) wavelet denoising. The wavelet denoising technique resulted in the highest coefficient of determination (R 2 = 0.856) for nitrate prediction. These noise removal techniques could not remove specular reflection effects and band overlap. To overcome these problems, a continuous wavelet transform, which could remove specular reflection as well as minimize noise, was used to deconvolute the soil spectral data, resulting in a high correlation (R 2 = 0.878) between soil nitrate content and MIR diffuse spectral reflectance.

Effect of interfacial specular electron reflection on the anisotropic magnetoresistance of magnetic thin films

We investigated the effect of specular reflection on the anisotropic magnetoresistance (AMR) of magnetic thin films. The sheet conductance is calculated as a function of the angle between magnetization and current from the microscopic transport parameters by using an extension of the Fuchs–Sondheimer theory. The calculation combines specular reflection on the film interfaces with mean-free paths which depend on the angle between the local magnetization and the electron velocity. The theoretical results are compared with experimental ones. Specular reflection can explain the quite large AMR amplitude observed in thin NiFe films used in the last generation of AMR heads.

Incident angle dependence of backscattered light by regolith layers

We have performed laboratory measurements of backscattered light by regolith layers to investigate the scattering properties of surfaces with regolith particles such as an asteroid surface. The samples used for our measurements are different types of surfaces consisting of alumina ( Al 2 O 3) plates, particles, and combination of both. We measured the backscattered light reflectance by varying the incident angle to the surface at small phase angle (1°). The reflected light from the plates covered by the thin layer of the particles has an effect of Fresnel specular reflection by the plates at small incident angle, and decreases as the incident angle increases but the rate of decrease is smaller than that of the bare plates. The results of our measurements will be used as the reference data for in situ photometric observations by a CCD camera onboard MUSES-C, the Japanese asteroid sample return mission which will be launched in 2002.

On optical performance and directional characteristics of plastic film liquid layer solar water heaters

An analysis is developed for the investigation of the transmittance–absorptance product ( τα), and directional characteristics of plastic-film water-bag solar water-heaters, which are important for long-term system performance investigations. The analysis allows a complete comparative investigation of the effects of a large number of parameters, like water layer thickness, bottom solar absorptance, radiation transmission conditions and extinction properties of semi-transparent films, on the transmittance–absorptance product. Finally the comparative effect of diffuse and specular reflection and transmission assumption on the derived results is investigated. It is concluded that the use of low iron content glass panes may possibly lead to ( τα) figures far in excess of 0.8 for new systems.

Shape reconstruction system integrating stereo vision and shape from shading with evolutionary programming

We propose a new method for measuring the shapes of objects. The proposed method is based on integrating stereo vision and shape from shading with evolutionary programming (EP). In some traditional methods, the reflection of objects is diffuse reflec- tion, but some methods cannot be applied to real objects because the reflection of real objects consists of diffuse and specular reflec- tion. Photometric stereo can be applied to real objects, but this method requires many original images to measure the shape accu- rately. The proposed method applies the Phong model to a reflec- tivity function and measures the shape of an object that has the diffused and specular reflection effect. Then this method uses EP to identify the reflectivity function accurately. © 1998 SPIE and IS&T. (S1017-9909(98)00101-9)

Shape Measurement Method by Integrating Stereo Vision and Shape-from-Shading with Evolutionary Programming.

In this paper, we propose a new method for measuring the shape of objects. The proposed method is based on integrating stereo vision and Shape-from Shading with Evolutionary Programming (EP). In some traditional methods the reflection of objects is diffuse reflection. But because the reflection of real objects consists of diffuse and specular reflection, some methods cannot be applied to real objects. Photometric stereo can be applied to real objects but this method needs many original image for measuring the shape accurately. The proposed method can apply Phong model to a reflectivity function and measure the shape of the object which have the effect of diffuse and specular reflection. Then, this method uses EP for identifying the reflectivity function accurately.

Shape from Shading with a Generalized Reflectance Map Model

Most conventional SFS (shape from shading) algorithms have been developed under three basic assumptions on surface properties and imaging geometry to simplify the problem, namely, a Lambertian surface, a distant point light source and orthographic projection. In this research, we derive a physics-based generalized reflectance map model which includes diffuse and specular reflection effects, a nearby point light source and perspective projection, and then we develop a new direct shape recovery algorithm from shaded images. The basic idea of our solution method is to discretize the image irradiance equation with a finite triangular element surface model, to express the resulting nonlinear system of equations in terms of depth variables only and to recover the object shape by linearizing the nonlinear equations and minimizing a quadratic cost functional. We perform numerical experiments with one or multiple photometric stereo images to demonstrate the performance of the derived physics-based reflectance map model and the proposed SFS algorithm.

The CW laser-induced temperature profile in a silicon substrate with an etched hole

This paper describes an analytical method to deduce the steady-state, laser-induced temperature profile in an isotropic silicon substrate with a Gaussian-shaped hole on its surface. Although effects of first-order specular reflection are included, the model is only applicable to holes that are not too deep. On carrying out a separate numerical finite-element analysis, the analytical method was found to be reasonably accurate. For a laser beam with a Gaussian intensity profile, it was found that the difference in results obtained by the two methods increases and then decreases as the Gaussian-shaped etched hole gets deeper. The analytical model tends to predict a lower peak temperature rise on the surface. Limitations of the analytical method are also discussed.

A new certainty grid based mapping and navigation system for an autonomous mobile robot

A complete Bayesian derivation for a sensor data updating formula for certainty grids is given, and its validity confirmed in a simulation. In the real world this formula alone is less valid because of the specular reflection effect, which seriously detracts from the map quality. A simple and practical approach, which greatly enhances the map quality in spite of some loss of range information, is proposed to compensate for this. A new path planning method based on the enhanced map is implemented on a mobile robot, and every aspect of the new algorithm is investigated through a series of experiments. The results show the validity and usefulness of the proposed approaches, i.e. updating formulae, specular reflection correction and path planning methods.

Radiation heat transfer of a Czochralski crystal growth furnace with arbitrary specular and diffuse surfaces

A numerical method is presented for predicting radiation heat transfer from axisymmetric bodies consisting of numerous arbitrary ring elements. Each ring element has the combined characteristics of specular and diffuse surfaces. The accuracy of the method was verified using a simple configuration. Good agreement between the present numerical and analytical solutions was obtained, and the effect of specular reflectivity was investigated. As a numerical example, radiation heat transfer of the Czochralski crystal growth apparatus was presented. The effect of specular reflection on temperature distribution on the various surfaces was examined. The present radiation transfer method was combined with the finite element package ABAQUS for conduction analysis, and the effect of specular reflectivity on temperature distribution and surface heat flux was investigated.

Comparison between experimental and theoretical rocking curves in extremely asymmetric Bragg cases of X-ray diffraction

Double-crystal rocking Curves from a highly perfect silicon crystal were taken in extremely asymmetric schemes, in which the glancing angles of the incident X-rays were very close to the critical angle of total external reflection. The experimental rocking curves were compared with theoretical calculations based both on an ordinary dynamical theory of diffraction and also on an extended dynamical theory, which uses a more exact solution of the fundamental equation of the dynamical theory and takes the effect of specular reflection into account. It is demonstrated from such a comparison that, in the case of extremely asymmetric diffraction, the ordinary treatment of the dynamical theory of diffraction is not valid; in contrast, the extended theory explains the rocking curve very well.

Effects of Sample Dilution and Particle Size/Morphology on Diffuse Reflection Spectra of Carbohydrate Systems in the Near- and Mid-Infrared. Part I: Single Analytes

The mid- and near-infrared diffuse reflection spectra of three carbohydrates—microcrystalline cellulose, wheat starch, and sucrose—are examined to determine whether dilution is necessary in either spectral region in order to avoid the effects of specular reflection. As expected, it was found that dilution was not necessary to obtain valid diffuse reflection spectra of samples in the near-infrared, but that dilution was necessary for measuring mid-infrared diffuse reflection spectra free of the effects of specular reflection. The effects of particle size and sample morphology were investigated for sucrose crystals up to 2 mm in dimension. Depending upon the particle size and orientation, the effects of specular reflection can be observed in both near- and mid-infrared diffuse reflection spectra of sucrose. Surface roughness can allow a diffuse reflection component to be measured in the spectra of very large particles where a specular reflection mechanism would typically be expected to predominate.

Anomalous Dispersion Effects in Diffuse Reflectance Infrared Fourier Transform Spectroscopy: A Study of Optical Geometries

In this report, the two most common diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) optical geometries (on-axis and off-axis) are investigated in terms of adherence to the Kubelka-Munk theory. It was found that specular reflection, whether in the form of regular Fresnel reflection or diffuse Fresnel reflection, is the major cause of spectral distortion in typical diffuse reflectance measurements. A discussion of the origin of the variation in specular background associated with resonances is presented. Once the adverse effects of specular reflection are minimized, the linear relationship between response and concentration predicted by Kubelka-Munk theory was found to extend to concentrated samples. Up to a point, this was the case even for intense absorption bands where anomalous dispersion leads to large changes in specular intensity.

Channeling studies in strained-layer epitaxial structures

The use of planar and axial channeling to measure the magnitude of the tetragonal distortion (and hence the strain) in simple strained-layer systems has been investigated. The test structures consisted of a 250 Å epitaxial In x Ga 1− x As layer sandwiched between a (100) GaAs substrate and a thin (250–360 Å) surface GaAs epilayer. The In concentrations were sufficiently high (0.10–0.16) so that the resulting tilt or kink angle, Δ, at the buried interface exceeded the planar critical angle ψ c for the 2.0 MeV 4He + beam. Complications in the observed axial and planar angular scans in the InGaAs layer have been studied in detail and suitable methods for extracting the correct values of Δ have been established. Planar channeling measurements, corrected for specular reflection effects in the GaAs surface layer, give Δ values in very good agreement with those calculated from the indium content. Axial channeling, however, can only be used to determine Δ when the surface GaAs overlayer is thinner than d/ψ c , where d is the spacing between atomic strings.

Comparison of Joint Canada‐U.S. Ocean Wave Investigation Project synthetic aperture radar data with internal wave observations and modeling results

Comparisons are made of L band and X band SAR images with in situ measurements of surface currents and surface wave spectral perturbations for two of the Joint Canada‐U.S. Ocean Wave Investigation Project internal wave data sets. Predicted and observed perturbations show agreement to within approximately a factor of 2 for L band, while the agreement at X band is much less satisfactory. Comparison of predicted microwave backscatter at X band with near‐surface radar measurements indicates large discrepancies even when surface tilt and specular reflection effects are included in the model. Synthetic aperture radar (SAR) X band modulations compare favorably with near‐surface radar measurements for range‐traveling internal waves, but for other directions, the SAR modulations are smaller than the near‐surface radar measurements. Simultaneous X and L band SAR images show comparable internal wave modulations.

Atmospheric optical depth effects on angular anisotropy of plant canopy reflectance

The effects of varying atmospheric aerosol optical depth on the bidirectional reflectance distribution of vegetation canopies is investigated. The reflectance distributions of two pasture grass canopies and one soya bean canopy under different sky irradiance distributions were measured, and the data were analyzed in the visible and IR spectral bands. It is observed that, for the pasture grass canopies, the change in reflectance is due to the percentage of shadowed area viewed by the sensor, and for the soya bean, the specular reflection effect and increased diffuse irradiance penetration into the canopy cause reflectance changes. It is detected that the reflectivity for the soya bean canopy on a hazy day is lower than on a clear day; however, the opposite change is observed for the pasture grass. It is also detected that the normalized difference vegetation index values differ under clear and hazy conditions for the same vegetation canopy conditions.