Spectral reflectivity

When considering light of a certain spectral energy distribution falling on an object with a given spectral reflectance and perceived by an eye with its own spectral response, to obtain the perceived color stimulus it is necessary to multiply these factors together as ia Eigure 6. Standards are clearly required for both the observer and the illuminant. 

Fig. 6. The stimulus perceived as color is made up of the spectral power (or, as here, energy) curve of a source times the spectral reflectance (or transmittance) curve of an object times the appropriate spectral response curves (one shown here) of the eye (3).

INHERENT CONTRAST SPECTRAL REFLECTANCE (COLOR),SIZE.SHAPE, DISTANCE, PATTERN, HORIZON,... 

Fig. 10. The spectral reflectance of CBCF and etched beryllium over the wavelength range 2 to 55 pm [16].

Fig. 4 Explanation of the fluorescence-quenching effect [2]. — (A) chromatograms of the same quantities of saccharin and dulcin observed under UV 254 light, (B) schematic representation of fluorescence quenching, (C) spectral reflectance curves of saccharin and dulcin.

Fig. 4. Spectral reflectance measurements in copper telluride halides. (Redrawn from A. Rabenau, H. Rau, and G. Rosenstein, Solid State Commun. 7, 1281 (1969), Fig. 1,...

Delori, F. C. and K. P. Pflibsen (1989). Spectral reflectance of the human ocular fundus. Applied Optics 28 1061-1077. 

In Eqs. (7)—(10), 5(A) is the spectral power distribution of the illuminant, and R A) is the spectral reflectance factor of the object. Jc(A), y(A), and 5(A) are the color-matching functions of the observer. In the usual practice, k is defined so that the tristimulus value, Y, for a perfect reflecting diffusor (the reference for R A)) equals 100. Using the functions proposed by the CIE in 1931, y(A) was made identical to the spectral photopic luminous efficiency function, and consequently its tristimulus value, Y, is a measure of the brightness of objects. The X and Z values describe aspects of color that permit identification with various spectral regions. 

The spectral reflectivity of the sensing film before and after the exposure to different vapors (all a.tP/P0 = 0.1) is illustrated in Figs. 4.7 and 4.8. Similar to other photonic nanostructured sensors8 19 34 35, the spectral shifts upon response to low vapor concentrations are relatively small. Thus, to accentuate the subtle differences due to vapor response, we measured the differential reflectance spectra AR as described by equation (4.1). 

Fig. 4.7 The spectral reflectivity of the sensing film measured over the range 400 1,000 nm before (solid line) and after (dotted line) the exposure to different vapors (all at P/P0 0.1) (a) water,...

Figures 7.5 and 7.6 give the measured spectral reflectances and transmittances of fabrics. It is clear from Figure 7.5 that color (6,white 7,black 1,yellow) has a significant effect in reflecting solar irradiance, and also we see why these colors can be discriminated in the visible spectral region of 0.6 pm. However, in the spectral range relevant to fire conditions, color has less of an effect. Also, the reflectance of dirty (5a) or wet (5b) fabrics drop to <0.1. Hence, for practical purposes in fire analyses, where no other information is available, it is reasonable to take the reflectance to be zero, or the absorptivity as equal to 1. This is allowable since only thin fabrics (Figure 7.6) show transmittance levels of 0.2 or less and decrease to near zero after 2 pm.

Two objects with different spectral properties, i.e., variation in the slope of spectral reflectance curve of two bands, can be separable with the help of ratio images (Lillesand et al. 2007). In this study standard reflectance data of USGS Spectral Library and John Hopkins University spectral library (Available in ENVI) have been used. To enhance the dissimilarity between different rock types in the scene, plots with a higher reflectance were kept in the numerator and plots with low reflectance were kept in the denominator, while taking the band ratios. Using this approach, a ratio of 5/3 was taken for basalt, 7/3 for peridotite, and 4/2 for vegetation. 

A simple test to estimate the interfacial layer thickness is to measure the thickness of the bottom layer before and after spinning, exposure, and development of the top layer. The difference is taken to be the thickness of the interfacial layer for comparison purposes. In reality, the mixing is continuous and the development of the top layer stops inside the interfacial layer instead of at its edges precisely. Furthermore, the test in Reference 26 relies on the IBM Film Thickness Analyzer to measure the resist thickness for convenience. Since this tool operates on the principle of spectral reflectivity changes caused by film thickness changes, a uniform refractive index is important. When some part of the interfacial layer still remains, the measurement can be erroneous in principle. 

P.Y. Bames, E.A. Early and A.C. Parr, NIST measurement services Spectral reflectance. NIST Special Publication, SP250-48, 1988. 

Fig. 16.12 Visible spectral reflectance (left), absorbence (middle) and 2nd derivative of absorbence (right) curves of two ground soil samples from a red B horizon of a Haplustox and a yellow B horizon of a Palexeralf (Torrent. Barron, 1993, modified with permission courtesy). Torrent).

In some cases, thermal neutrons can also be used to measure the absolute abundances of other elements. Transforming the neutron spectrum into elemental abundances can be quite involved. For example, to determine the titanium abundances in lunar spectra, Elphic et at. (2002) first had to obtain FeO estimates from Clementine spectral reflectances and Th abundances from gamma-ray data, and then estimate the abundances of the rare earth elements gadolinium and samarium from their correlations with thorium. They then estimated the absorption of neutrons by major elements using the FeO data and further absorption effects by gadolinium and samarium, which have particularly large neutron cross-sections. After making these corrections, the residual neutron absorptions were inferred to be due to titanium alone. 

Figure 3. Spectral reflectance curves of some inorganic pigments in paints...

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