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The spectral hemispherical reflectance in frequency and spectral hemispherical reflectance in wavelength of a surface, denoted R ν and R λ respectively, are defined as [1] =,,, =,,, where Φ e, ν r is the spectral radiant flux in frequency reflected by that surface;
Formally, the wavelength version of Wien's displacement law states that the spectral radiance of black-body radiation per unit wavelength, peaks at the wavelength given by: = where T is the absolute temperature and b is a constant of proportionality called Wien's displacement constant, equal to 2.897 771 955... × 10 −3 m⋅K, [1] [2] or b ...
Mathematically, for the spectral power distribution of a radiant exitance or irradiance one may write: =where M(λ) is the spectral irradiance (or exitance) of the light (SI units: W/m 2 = kg·m −1 ·s −3); Φ is the radiant flux of the source (SI unit: watt, W); A is the area over which the radiant flux is integrated (SI unit: square meter, m 2); and λ is the wavelength (SI unit: meter, m).
A consequence of Wien's displacement law is that the wavelength at which the intensity per unit wavelength of the radiation produced by a black body has a local maximum or peak, , is a function only of the temperature: =, where the constant b, known as Wien's displacement constant, is equal to + 2.897 771 955 × 10 −3 m K. [31]
The transmittance or reflectance value for each wavelength of the test sample is then compared with the transmission or reflectance values from the reference sample. Most instruments will apply a logarithmic function to the linear transmittance ratio to calculate the 'absorbency' of the sample, a value which is proportional to the ...
The temperature Stefan obtained was a median value of previous ones, 1950 °C and the absolute thermodynamic one 2200 K. As 2.57 4 = 43.5, it follows from the law that the temperature of the Sun is 2.57 times greater than the temperature of the lamella, so Stefan got a value of 5430 °C or 5700 K. This was the first sensible value for the ...
Values of spectral parameters like reflectance can then be directly extracted from all pixels in the imagery, aggregated and averaged to produce a reflectance curve for spectral analysis. [ 6 ] [ 8 ] In terms of non-imaging spectroradiometry, data collection and sampling are usually conducted through direct scanning with spectroradiometers in ...
The n(λ) and k(λ) spectra of each film are obtained along with film thickness, over a wide range of wavelengths from deep ultraviolet to near infrared wavelengths (190–1000 nm). In the following examples, the notation for theoretical and measured reflectance in the spectral plots is expressed as "R-theor" and "R-meas", respectively.