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Black-body Radiation, Einstein and Planck's Law
Published in Caio Lima Firme, Quantum Mechanics, 2022
The black-body emits a light spectrum whose spectral radiance is dependent upon the temperature. The spectral radiance is the radiance (radiant flux emitted, reflected, transmitted or received by a given surface, per unit solid angle, in steradian unit, per unit projected area) of a surface per unit wavelength (or frequency). The unit of spectral radiance is watt per steradian per square meter, per meter (W. sr-1 .m-2.m-1). At room temperature, the black-body emits only infrared radiation. As the temperature increases, the black-body starts to emit visible light changing its color from red to blue. When it is white, it is emitting ultraviolet radiation. At each temperature, there is a distinguished energy distribution among different wave lengths.
Measurements and Assessment of Lighting Parameters and Measures of Non-Visual Effects of Light
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
Precise measurement of the SPD of light could be done using an adequate spectroradiometer. There are two main groups of spectroradiometers: double monochromator spectroradiometers and diode array spectroradiometers. Most double-monochromator spectroradiometers are fixed installation systems for laboratory measurements, while diode array ones are portable devices for field use. More precise measurements could be obtained by using double monochromator instruments. Using diode array spectroradiometers, one must take into account stray light, which may sometimes significantly affect the results. Depending on the application and expected result of measurement, more extensive information provided by the spectrum, higher precision of measurement, and possibly an in-depth analysis can be required. The portable spectroradiometer seems to be more suitable for evaluating optical radiation in such situations. Spectroradiometers make it possible to measure spectral radiance or irradiance in various spectral ranges, depending on the measuring possibilities of a particular device. A built-in optical measuring system commonly covers visual radiation from approximately 380 nm to 780 nm. As a general-purpose instrument, such a device has high accuracy and built-in system applications which allow the assessment of many aspects of light.
Remote Sensing Monitoring of Marine Oil Spills
Published in Lin Mu, Lizhe Wang, Jining Yan, Information Engineering of Emergency Treatment for Marine Oil Spill Accidents, 2019
Lin Mu, Lizhe Wang, Jining Yan
The relative magnitude of the object’s thermal radiation capacity at a given temperature is described as spectral radiance ɛ. In very narrow spectral bands (e.g., 8 ∼ 14 microns), when the measured object is close to the black body, the Planck formula and the integral mean value theorem are used to calculate the spectral radiance ɛ, and the expression is as follows: ε=cδTλT2where, c is a constant (1.44 × 10−2 meters · Kelvin); λ refers to the central wavelength of the spectral band; δT refers to the difference between the radiation temperature of the object and the thermometrical temperature (measured temperature); and T refers to the measured temperature of the object. In the case of marine remote sensing, since the radiance of the seawater is very low, close to 1, the seawater can be regarded as a black body. If the radiation temperature difference between the target (such as oil film) and the background seawater (δT) and the actual temperature of the seawater (T) are measured, the radiance of the target material can be calculated using the formula.
Reflectance spectroscopy and ASTER mapping of aeolian dunes of Shaqra and Tharmada Provinces, Saudi Arabia: Field validation and laboratory confirmation
Published in International Journal of Image and Data Fusion, 2023
Yousef Salem, Habes Ghrefat, Rajendran Sankaran
In addition, the spectral reflectances of the different sand fractions are measured in the visible to shortwave infrared (VNIR-SWIR, 0.4–2.5 μm) regions of the electromagnetic spectrum using a GER3700 spectrometer in the laboratory to understand the spectral absorption of minerals of the dunes and map the dunes. The measurement is carried out keeping the instrument vertically above the samples. The samples are illuminated at an incident angle of 30° and reflectances are measured in a rectangular field of view of 1.5 by 7 cm. The GER3700 spectrometer measures 640 bands between 0.315 and 2.519 μm at the spectral sampling range from 0.0015 to 0.012 μm (Ghrefat et al. 2007). The spectral radiance (W/m2/sr/nm) of a Spectralon (calibration material) is used as a reference to measure the spectral radiance of samples. The reflectance of samples is calculated from the ratio of two spectral radiance that is by dividing the radiance of the Spectralon by the radiance of the measured target.
Non-contact temperature measurement at the Physikalisch-Technische Bundesanstalt (PTB)
Published in Quantitative InfraRed Thermography Journal, 2021
I. Müller, A. Adibekyan, K. Anhalt, C. Baltruschat, B. Gutschwager, S. König, E. Kononogova, C. Monte, M. Reiniger, S. Schiller, D. R. Taubert, D. Urban, J. Hollandt
The emissivity of an object describes its ability to emit temperature radiation. It is defined as the ratio of the spectral radiance of the object to the spectral radiance of the blackbody at the same wavelength and temperature. As no object emits more temperature radiation than the blackbody, its value is in the range from 0 to 1. For the metrological characterisation and calibration of non-contact temperature measuring instruments, thermal radiation sources with an emissivity close to 1 are used. Especially with a cavity radiator, an emissivity very close to 1 and a Lambertian emittance characteristic can be achieved. The radiance of such a radiator can, therefore, be described in a very good approximation by Planck’s radiation law for a blackbody. However, in industrial and scientific applications, the observed objects generally have an emissivity very different from 1 and a precise knowledge of their emissivity is crucial to reliable temperature measurements.
Thermophysical Properties of Molten Stainless Steel Containing 5 mass % B4C
Published in Nuclear Technology, 2019
Hiroyuki Fukuyama, Hideo Higashi, Hidemasa Yamano
Normal spectral emissivity is defined as the ratio of normal spectral radiance emitted from a sample to that emitted from a blackbody at the same temperature.5 This value was determined from radiance measurements of the levitated sample droplet (mass: 1.0 ± 0.1 g). The PROSPECT experimental apparatus for the normal spectral emissivity measurement is shown in Fig. 1. Normal spectral radiation spectra from the top of the sample droplet were obtained using a multichannel spectrometer (spectral range: 530 to 1100 nm; USB2000, Ocean Optics Inc., Florida). The spectrometer was calibrated using a quasi-blackbody as a standard light source that was placed in the center of the radio-frequency coil of the PROSPECT. The quasi-blackbody was filled with Cu or NiC to serve as a temperature fixed point using the melting point of Cu (1084.62°C) or eutectic point of NiC alloy (1329°C), respectively, as shown in Fig. 1c. Radiance with a wavelength range from 780 to 1064 nm was measured by the spectrometer through a reflection with a dichroic mirror mounted between the sample and the spectrometer. A 3-T static magnetic field was applied to the sample droplet to suppress sample oscillation and translational motion. Three SS316L samples and three SS–5%B4C samples were used for the normal spectral emissivity measurement. The average experimental duration per sample was 40 min.