Shape Of Reflectance Spectra Research Articles

Effects of thermal treatment on the complex structure of luminescence emission of Li-doped ZnO screen-printed films

The ZnO–Li films were synthesized and investigated in an attempt to explore and develop RE-free phosphor materials capable of emitting intense visible light in a wide spectral range. The effects of both heterovalent doping with lithium and high-temperature annealing on the optical properties of ZnO films were studied. The films were deposited on the Al2O3 substrate using the screen-printing method and annealed at 800–1,000°C in air for 0.5–3 h. Both doping and annealing result in the transformation of the shape of reflectance spectra in the range of 300–400 nm and the shift of absorption edge to the long-wavelength region. At the same time, the bandgap value estimated taking into account the exciton peak position and its binding energy is independent of Li-doping. The feature at 300–400 nm and the shift of absorption edge are ascribed to the appearance of the absorption band that excited the yellow photoluminescence band. The photoluminescence spectra of undoped and Li-doped films show the emission bands in the ultraviolet and visible spectral ranges. The ultraviolet emission is due to ZnO exciton recombination. The visible emission band comprises several components peaked at 430, 482, 540, 575, and 640 nm. Their relative intensities depend on Li-doping, annealing temperature, and annealing duration. The 430- and 482-nm luminescence bands were observed in Li-doped films only. Their excitation spectra show the peak located at 330–340 nm, indicating that the energy significantly exceeds the ZnO bandgap energy. Consequently, the 430- and 482-nm luminescence bands are attributed to an additional crystal phase formed under annealing. Other components of visible emission bands are ascribed to the defect-related emission of ZnO. The possible nature of these bands is further discussed. Li-doping and annealing at intermediate temperatures result in blue emission and an enhancement of other visible bands, which makes ZnO–Li films a perspective material in photonic applications.

An Empirical Algorithm using Derivative Difference for Estimating Chlorophyll-A in Case-II Water

Water quality management includes measurement of quantity and quality. The abundance of phytoplankton in water body represents the physical condition and chemical constituents. As Chlorophyll-a exists in all types of phytoplankton, naturally the choice for water quality measurement is estimation of Chl-a concentration. The Chl-a concentration is estimated using various spectral reflectance algorithms such as single band regression, band ratio, three-band ratio, four-band ratio etc have been developed and is being used. Subsequently, the first order derivative ratio and second order derivative ratio methods are also used in some studies. Though such algorithms provide water quality measures, new algorithms are being introduced to improve estimation accuracy. In this paper, a new algorithm ‘Derivative Difference’ is proposed. It is based on the Chlorophyll concentration variation with shape of reflectance spectrum. The derivative data represents the slope of the reflectance data at different wavelength. The difference in derivative values at selected two different wavelengths were correlated with measured values to estimate Chl-a concentration. Obtained results were compared with the values obtained from band ratio method and derivative ratio methods. The algorithm is found to be better in some conditions.

Explanation for the contradiction between the results of Diallo et al. (doi:10.1016/j.jofri.2018.10.001) and Winklhofer et al. (doi:10.1097/RLI.0000000000000032) in differentiating ferromagnetic from nonferromagnetic bullets by means of the dual-energy index

In the present study, a series of reflectance spectra of postmortem lividity, pallor, and putrefaction-affected skin for 195 investigated cases in the course of cooling down the corpse has been collected. The reflectance spectrometric measurements were stored together with their respective metadata in a MySQL database. The latter has been managed via a scientific information repository. We propose similarity measures and a criterion of similarity that capture similar spectra recorded at corpse skin. We systematically clustered reflectance spectra from the database as well as their metadata, such as case number, age, sex, skin temperature, duration of cooling, and postmortem time, with respect to the given criterion of similarity. Altogether, more than 500 reflectance spectra have been pairwisely compared. The measures that have been used to compare a pair of reflectance curve samples include the Euclidean distance between curves and the Euclidean distance between derivatives of the functions represented by the reflectance curves at the same wavelengths in the spectral range of visible light between 380 and 750 nm. For each case, using the recorded reflectance curves and the similarity criterion, the postmortem time interval during which a characteristic change in the shape of reflectance spectrum takes place is estimated. The latter is carried out via a software package composed of Java, Python, and MatLab scripts that query the MySQL database. We show that in legal medicine, matching and clustering of reflectance curves obtained by means of reflectance spectrometry with respect to a given criterion of similarity can be used to estimate the postmortem interval.

KARAKTERISTIK SPEKTRAL ELEKTROMAGNETIK SPECIES DOMINAN PADA HUTAN RAWA GAMBUT KALIMANTAN TENGAH (Electromagnetic Spectral Characteristics of Dominant Species at the Peat-Swamp Forest at Central Kalimantan)

ABSTRACTThis paper reports the results of the spectral library from dominant trees in peat-forest in Central Kalimantan, Indonesia supported under JST-JICA Project: “Wild Fire and Carbon Management in Peat Forest in Indonesia”. Spectral libraries are commonly established as a means to archive representative signatures of natural materials. Such signatures can then be used to train feature extraction and classification algorithms applied to remote sensing data imagery. Spectral analyses were performed to the 33 dominant species in peat-forest in Central Kalimantan, Indonesia obtained during the field survey measurement (in-situ measurements) and airborne campaign by HYMAP sensor in 2011-2014. We found, each vegetation type has unique spectral signature or characteristics. The shapes of reflectance spectra can be used for identification of vegetation types combine with remote sensing data (airborne and satellite images).
 Keywords: Spectral library/signature, Peat-Forest, Spectroradiometer, Vegetation and Kalimantan

Optical properties of mesoporous one-dimensional photonic crystals

The systematic features in the reflectance spectra of broadband optical radiation from the surface of one-dimensional photonic crystals based on mesoporous structures are presented. The dispersion dependence for electromagnetic waves in the mesoporous one-dimensional photonic crystal is established. On its basis, reflectance and transmittance spectra are calculated for particular structures, and the microscopic parameters of the samples under study are determined. The developed theory is used to explain the shape of reflectance spectra in mesoporous photonic crystals based on silicon, quartz, and aluminum oxide.

317 構造色解析とその可視化に関する検討(OS1-3 最適設計と解析)

Structural color comes out of scattering and interference on specific wavelength light by microstructure, it's differ from pigments. If structural color can visualized, it lead to solution of relation between structure and color. In structural color, the color generally evaluated by reflection spectrum. But it's difficult that understand or confirm a color intuition only a graph of reflection spectrum. In this study, structural color is visualized in CIE color system and HSV color system. Reflection spectrums of a male adult Red-flanked bluetail's feather that calculated by finite element method (FEM) are indicated by the two color systems. If absorption is not present, a result color was bluish color. If absorption is present, a result was greenish color. These results agree with a shape of reflection spectrum.

Factors affecting the measurement of CDOM by remote sensing of optically complex inland waters

A combination of new measurements and analysis of historical data from several geographic regions was used to address four issues that affect the reliability and interpretation of colored dissolved organic matter (CDOM) measured by remote sensing of inland waters. First, high variability of CDOM levels in lakes and rivers was found at seasonal and multi-year time scales and at shorter intervals in some rivers and lakes. Coefficients of variation (CVs) of 30%–50% for absorptivity at 440nm (a440) were common in historical and new data sets we examined. CDOM values used to calibrate imagery thus should be measured close to the image acquisition date, preferably within 1–2 months in lakes and a few days in large rivers, unless it can be shown that CDOM levels are temporally stable over longer (or shorter) time periods in a given aquatic system. Second, spectral slopes (S) for CDOM in the visible range vary little over time (even over multi-year periods) within sites. Substantial variation was found between sites, however, and most spectra showed a change in slope near 460nm. Values of S400–460 for waters with moderate to high CDOM levels generally were within a narrow range (~0.014–0.018) and similar to reported S values in the near UV. Values of S400–460 for waters with low CDOM generally were smaller and more variable, as were values for S460–650 for all waters. Overall, the variability of spectral slopes in the visible range should not have a large effect on the reliability of a440 estimates made from remote sensing, which in many models involve reflectance measurements at wavelengths>500nm. Third, although a strong correlation (r2=0.925) was found between CDOM levels and DOC concentrations in 34 surface waters sampled in 2013, the standard error of estimate suggests an uncertainty of~±20% in predicting DOC at a440=5m−1 (a moderate CDOM level). Moreover, CDOM–DOC relationships for unpublished data sets we analyzed and those reported in the literature indicate that both the fraction of DOC that is colored and slopes of regressions between CDOM and DOC are highly variable in space and time. Prediction of DOC concentrations in water bodies from CDOM levels (whether measured in the laboratory or by remote sensing) thus is associated with considerable uncertainty. For the present, this implies that field sampling is required to verify DOC concentrations predicted from remotely sensed CDOM measurements until we have a better understanding of variations in DOC–CDOM relationships. Fourth, shapes of reflectance spectra for CDOM-rich waters varied greatly depending on the concentrations of other constituents (suspended solids and chlorophyll) that affect the optical properties of water. Nonetheless, it is not obvious from our results for several predictive models that different remote sensing algorithms are needed to calculate CDOM levels accurately for waters where CDOM is the only variable affecting reflectance versus waters where other constituents also affect the spectra. The best band or band ratio models for simulated Landsat 8, Sentinel-2 and Sentinel-3 bands from field measured reflectance spectra yielded high r2 values (0.84–0.86) for a440. The broader Landsat 8 bands worked nearly as well for a440 as the narrower Sentinel band sets and hyperspectral bands, probably because CDOM is characterized by a broad exponential increase in absorbance with decreasing wavelength rather than specific peaks or troughs in absorbance or reflectance.

Similarity Analysis of Spectra Obtained via Reflectance Spectrometry in Legal Medicine

In the present study, a series of reflectance spectra of postmortem lividity, pallor, and putrefaction-affected skin for 195 investigated cases in the course of cooling down the corpse has been collected. The reflectance spectrometric measurements were stored together with their respective metadata in a MySQL database. The latter has been managed via a scientific information repository. We propose similarity measures and a criterion of similarity that capture similar spectra recorded at corpse skin. We systematically clustered reflectance spectra from the database as well as their metadata, such as case number, age, sex, skin temperature, duration of cooling, and postmortem time, with respect to the given criterion of similarity. Altogether, more than 500 reflectance spectra have been pairwisely compared. The measures that have been used to compare a pair of reflectance curve samples include the Euclidean distance between curves and the Euclidean distance between derivatives of the functions represented by the reflectance curves at the same wavelengths in the spectral range of visible light between 380 and 750 nm. For each case, using the recorded reflectance curves and the similarity criterion, the postmortem time interval during which a characteristic change in the shape of reflectance spectrum takes place is estimated. The latter is carried out via a software package composed of Java, Python, and MatLab scripts that query the MySQL database. We show that in legal medicine, matching and clustering of reflectance curves obtained by means of reflectance spectrometry with respect to a given criterion of similarity can be used to estimate the postmortem interval.

Progress in the development of deposition prevention and cleaning techniques of in-vessel optics in ITER

The lifetime of front optical components unprotected from reactor grade plasmas may be very short due to intensive contamination with carbon and beryllium-based materials eroded by the plasma from beryllium walls and carbon tiles. Deposits result in a significant reduction and spectral alterations of optical transmission. In addition, even rather thin and transparent deposits can dramatically change the shape of reflectance spectra, especially for mirrors with rather low reflectivity, such as W or Mo. The distortion of data obtained with various optical diagnostics may affect the safe operation of ITER. Therefore, the development of optics-cleaning and deposition-mitigating techniques is a key factor in the construction and operation of optical diagnostics in ITER. The problem is of particular concern for optical elements positioned in the divertor region. The latest achievements in protection of in-vessel optics are presented using the example of deposition prevention/cleaning techniques for in-machine components of the Thomson scattering system in the divertor. Careful consideration of well-known and novel protection approaches shows that neither of them alone provides guaranteed survivability of the first in-vessel optics in the divertor. Only a set of complementary prevention/cleaning techniques, which include special materials for mirrors and inhibition additives for plasma, is able to manage the challenging task. The essential issue, which needs to be addressed in the immediate future, is an extensive development of techniques tested under experimental conditions (exposure time and contamination fluxes) similar to those expected in ITER.

Field spectroscopy of estuarine intertidal habitats

The recent introduction of portable, low‐cost hyperspectral radiometers for measuring the reflectance of marine intertidal habitats has considerable promise, first as a source of reference spectra for airborne and satellite remote sensing, and second as a survey technique in its own right. This paper reports on the results of an intercalibration exercise in which two designs of commercially available instruments were used to measure reflectance spectra across a diverse, intertidal site. The substrates sampled included seagrasses, macroalgae, and sediments which varied in wetness and grain size. Spectra were compared statistically using several measures of similarity, and the results showed a high degree of correlation between the measured reflectance spectra. There were no significant differences between instruments from different manufacturers in the shape of reflectance spectra, but the signal‐to‐noise ratio varied considerably between individual instruments. Spectra measured by operators with lesser experience in field spectrometry tended to be more variable than those of more experienced operators, indicating that training and adherence to set protocols are important when implementing this method in the field situation. Spatial plots derived from field spectra showed essentially the same trends in surface features as plots created using traditional sampling and remote sensing methods. Furthermore, the use of field spectrometry as a stand‐alone, low‐cost method for rapidly mapping the distribution of major habitat types was demonstrated by the results of a survey of a large intertidal sandbank.

Utilization of embedded optical fibre sensors for delamination characterization in compositelaminates using a static strain method

Embedded fibre Bragg grating (FBG) sensors are utilized to characterize a delamination inglass fibre-reinforced epoxy (GF/EP) composite laminates using a static strain method.Composite beams with different edge delaminations in the thickness-wise direction aremonitored by the FBG sensors, whose centres are located at delamination tips of thebeams, under a three-point bending test. A surface bonded strain gauge is employed tocalibrate the FBG sensor using the bending test. Moreover, strain distribution within thesensing region of the delaminated composite beams is numerically calculated by thefinite element method (FEM). FEM results establish the relationship between thestrain distribution of the beams and the shape of reflection spectra from theFBG sensors. A correlation between delamination location in the thickness-wisedirection of the beams and the shape of the reflection spectra is then highlighted.

Determination of exciton transition energy and bowing parameter of AlGaN alloys in AlGaN/GaN heterostructure by means of reflectance measurement

The normal-incidence reflectance measurement was employed to obtain the free exciton transition energy (EFX) of AlGaN alloys in AlxGa1−xN/GaN/sapphire heterostructure grown by metalorganic chemical vapor deposition. It was found that the thickness variation of the AlGaN layer may cause a noticeable change in the line shape of reflectance spectrum and impede the identification of the desired excitonic position. By using a reflection model of two absorbing layers with a transparent substrate, the experimental reflectance spectra were theoretically simulated and utilized to explain the reflection mechanism in AlxGa1−xN/GaN heterostructures. On the basis of the above analysis, the feasibility of the reflectance measurement for such heterostructures is confirmed. At room temperature, the EFXs obtained from the fitting showed an excellent agreement with the corresponding peak energies in the photoluminescence spectra. Furthermore, at the optical energy position about 100 meV above the EFX, the spectral feature of exciton-LO phonon interaction was observed in the reflectance spectrum record for low Al composition (x⩽0.16). Using the Al mole fraction derived from x-ray diffraction measurement, the bowing parameter of the epitaxial AlGaN layer was determined. In the range of 0⩽x<0.3, the resulting bowing parameter shows a downward value of 0.53 eV.

Effect of connective tissue on the shape of reflectance spectra obtained with a fibre-optic fat-depth probe in beef

A fat-depth probe was fitted with optical fibres to combine depth detection with spectrophotometry and fluorometry. Measurements were made through forelimb flexor, triceps brachii and longissimus thoracis muscles on 22 beef carcasses in a meat cooler. All strong fluorescence peaks had matching strong reflectance peaks (presumably connective tissue), but some strong reflectance peaks did not have equivalent fluorescence peaks (presumably adipose tissue). When the probe stopped at full depth and a complete reflectance spectrum was obtained, no effect from adipose tissue at the optical window of the probe was detected, whereas connective tissue increased reflectance across the visible spectrum ( P < 0.005). The strongest effect was at 600 nm. Thus, spuriously high reflectance readings obtained with a fibre-optic meat probe are more likely to originate from connective tissue than from intramuscular adipose tissue.

Multiple scattering in the remote sensing of natural surfaces

Radiosity models, working at scales much greater than the wavelength of light, predict the amount of light scattered many times (multiple scattering) among scene elements in addition to light interacting with a surface only once (single scattering). Such models are little used in remote-sensing studies because they require accurate digital terrain models and, typically, large amounts of computer time. We have developed a practical radiosity model that runs relatively quickly within suitable accuracy limits, and have used it to explore problems caused by multiple scattering in image calibration, terrain correction, and surface roughness estimation for optical images. We applied the model to real surfaces spatial scales of 30 m and 1 cm, separating multiple-scattering effects into those resolved by the Landsat TM and unresolved subpixel effects. Calculated radiosities were used to estimate quantitatively the magnitude of the multiple-scattering effects for different solar illumination geometries, surface reflectivities, sky illuminations and surface roughnesses. At the 30-m scale, multiple scattering can account for as much as 10 per cent of the radiance from sunlit slopes, and much more for shadowed slopes; at the 1-cm scale, the multiple scattering can locally account for as much as 70 per cent. Because the amount of multiple scattering increases with reflectivity as well as roughness, multiple scattering effects will distort the shape of reflectance spectra as well as changing their overall amplitude. Our results have significant implications for determining reflectivity and surface roughness in remote sensing and for energy-balance calculations.

Grain size of the surface regolith of asteroid 4 Vesta estimated from its reflectance spectrum in comparison with HED meteorites

Abstract— The grain‐size distribution of the regolith of asteroid 4 Vesta has been estimated by comparing its reflectance spectra (0.3–2.6 μm) with those of HED meteorites. The finest grain‐size separate (&lt;25 μm) of a particular howardite has a reflectance spectrum most similar to Vesta's. In order to better simulate Vesta's surface mineralogy, reflectance spectra of those finest HED meteorite powders were linearly combined, and Vesta's spectrum was scaled for the best fit between them. Both the albedo and the shape of reflectance spectrum of Vesta were well reproduced by regional mixtures of the finest (&lt;25 μm) powders of HED meteorites. The result suggests the heterogeneity of Vesta's surface and provides an estimate of the visible reflectance of Vesta that is close to its IRAS albedo. Thus, this suggests that fine grains can be generated and retained by relatively small bodies (Vesta is approximately 500 km in diameter).