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Ultrasonic Sensors
Published in Bogdan M. Wilamowski, J. David Irwin, Control and Mechatronics, 2018
Acoustic wave propagation is disturbed by changes in the acoustic impedance of the medium, which is defined as the product of medium density and speed of sound. Discontinuities of the acoustic impedance can occur when the lower impedance of air meets solid objects with higher impedance and scattering of the acoustic wave results. When scattered waves make their way back to a receiver, an echo is registered. There are two basic types of scattering: reflection and diffraction. Reflection occurs from smooth surfaces with the angle of incidence to the normal of the surface equaling the angle of reflection. Smooth is defined by the size of rough features of the surface being much smaller than the acoustic wavelength. Reflection from smooth surfaces is often called specularity. Diffraction occurs due to discontinuities of the surface, such as edges (i.e., where a smooth surface ends or changes direction). Reflection from smooth planes and corners, and diffraction from edges will be considered here. More complex target profiles may be analyzed using approximations developed by Freedman [4].
Daylighting and Glare
Published in Kjell Anderson, Design Energy Simulation for Architects, 2014
Light may reflect primarily in one direction, or it may diffuse into nearly all directions equally. The concentration of the reflected light is called specularity. Specularity is a ratio that ranges from 0 (perfectly diffuse, with light bouncing equally in all directions) to 1 (perfectly specular, with light reflecting only in one direction). Velvet is close to 0, while a mirror is close to 1.
Pattern Discovery from Eroded Rock Art
Published in Filippo Stanco, Sebastiano Battiato, Giovanni Gallo, Digital Imaging for Cultural Heritage Preservation, 2017
Filippo Stanco, Sebastiano Battiato, Giovanni Gallo
To construct PTM, we need to know the light position, including the lighting direction and distance between the light source and the rock surface. One simple approach is to build a light hemispheric cage with fixed-light positions. Automatic control of lights and camera can acquire a PTM with great speed, e.g., between 5 and 15 minutes. However, fixed-light position equipment has its disadvantages. The light distance from the subject limits the object diameter [33]. The bigger subjects require proportionally larger cage size and a more powerful lamp. To avoid using an elaborate light stage with a known light source position, the user may position a handheld light source at varying locations, and the software can recover the lighting direction from the specular highlights produced on a black sphere included in the field of view captured by the camera [33]. To measure and manage the light source radius, the “Egyptian Method” can be applied. This low-tech approach is to use one string with one end tied to the light source and another end tied to the center of the subject. Two people can hold each end straight. So the light distance is measured and the light held steady. A look-up table of distance-dependent light power values can help the field workers to change the string length and light power at the same time. The per-pixel surface normals are extracted from the representation to enhance the surface details. For example, specular enhancement. Simulation of specularity is particularly effective at enhancing the perception of surface shape. This is important to discover patterns in rock art. PTM requires only a single camera and a light for which the angle and distance can be measured. PTM is a low-energy technique that is desirable for field applications. This method has been used to discover a 3,000-year-old cuneiform tablet. The interactive texture map viewer is available online [19] and it has been popular in the archeologist community. Unlike photometric stereo or laser scans, PTM is implemented without the use of 3D geometry, eliminating 3D geometry’s associated costs in terms of hardware and software. However, PTM does not provide any depth information which is often useful to study the packing patterns.
An approach to mitigate effects of colour variation, specularity and pores on microtexture analysis of aggregates
Published in International Journal of Pavement Engineering, 2020
Abolfazl Ravanshad, Sanghyun Chun, Reynaldo Roque, George Lopp
Images were obtained by scanning aggregate particles for virgin and MD-polished conditions with different illuminations. Figure 3 illustrates the results matrix, which was produced to take several factors into account. The first factor considered was the effect of colour variation on TI. All granites and siliceous wackestone, and one limestone (HN717) showed highly non-uniform colour pattern. However, all other limestones were uniform in colour. The second factor was the type of analysis either existing AIMS approach using a single image or new PS-ICA approach using multiple images. Lastly, the third factor was the light intensity to mitigate specularity effect on TI. All limestones, which may not exhibit specularity effects, were scanned at default light intensity whereas granites and siliceous wackestone, which may exhibit relatively greater specularity effects, were evaluated at both default and modified (reduced) light intensities.
On the electrical conductivity of metals with a rough surface
Published in Philosophical Magazine, 2021
We proceed to examine in the semi-classical limit so as to shed some light on the meaning of the specularity parameter p introduced in the Fuchs–Sondheimer method. To this end, we make two conventional approximations, namely, where , with and . With these approximations, Equation (34) can be recast as where the sum in (34) over has been converted into an integration as usual.
The impact of greenery and surface reflectances on solar radiation in perimeter blocks
Published in Architectural Science Review, 2022
Barbara Szybinska Matusiak, Shabnam Arbab
where The red, green, and blue reflected components are Cr, Cg, and Cb, respectively. The photopic average of the RGB is Rd.Rs = Reflected specularitySr = surface roughnessTd = Diffuse transmissivity (fraction of light that passes through the surface diffusely).Ts = Transmitted specularity (fraction of light transmitted as a beam – that is, the fraction of light not diffusely scattered)