Relative Reflectance Spectra Research Articles

An Inorganic–Organic Hybrid Polymer Cocatalyst for Photoelectrochemical Water Oxidation with Dual Functions of Accelerating Kinetics and Improving Charge Transfer

Oxygen evolution cocatalysts (OECs) play important roles in improving the efficiency of photocatalysts in solar water splitting. Inorganic–organic hybrid polymers (IOHPs), which have good electroly...

Visual cues for woodpeckers: light reflectance of decayed wood varies by decay fungus

ABSTRACT The appearance of wood substrates is likely relevant to bird species with life histories that require regular interactions with wood for food and shelter. Woodpeckers detect decayed wood for cavity placement or foraging, and some species may be capable of detecting trees decayed by specific fungi; however, a mechanism allowing for such specificity remains unidentified. We hypothesized that decay fungi associated with woodpecker cavity sites alter the substrate reflectance in a species-specific manner that is visually discriminable by woodpeckers. We grew 10 species of wood decay fungi from pure cultures on sterile wood substrates of 3 tree species. We then measured the relative reflectance spectra of decayed and control wood wafers and compared them using the receptor noise-limited (RNL) color discrimination model. The RNL model has been used in studies of feather coloration, egg shells, flowers, and fruit to model how the colors of objects appear to birds. Our analyses indicated 6 of 10 decayed ...

The potential of hyperspectral images and partial least square regression for predicting total carbon, total nitrogen and their isotope composition in forest litterfall samples

The main objective of this study was to examine the potential of using hyperspectral image analysis for prediction of total carbon (TC), total nitrogen (TN) and their isotope composition (δ13C and δ15N) in forest leaf litterfall samples. Hyperspectral images were captured from ground litterfall samples of a natural forest in the spectral range of 400–1700 nm. A partial least-square regression model (PLSR) was used to correlate the relative reflectance spectra with TC, TN, δ13C and δ15N in the litterfall samples. The most important wavelengths were selected using β coefficient, and the final models were developed using the most important wavelengths. The models were, then, tested using an external validation set. The results showed that the data of TC and δ13C could not be fitted to the PLSR model, possibly due to small variations observed in the TC and δ13C data. The model, however, was fitted well to TN and δ15N. The cross-validation R2 cv of the models for TN and δ15N were 0.74 and 0.67 with the RMSEcv of 0.53% and 1.07‰, respectively. The external validation R2 ex of the prediction was 0.64 and 0.67, and the RMSEex was 0.53% and 1.19 ‰, for TN and δ15N, respectively. The ratio of performance to deviation (RPD) of the predictions was 1.48 and 1.53, respectively, for TN and δ15N, showing that the models were reliable for the prediction of TN and δ15N in new forest leaf litterfall samples. The PLSR model was not successful in predicting TC and δ13C in forest leaf litterfall samples using hyperspectral data. The predictions of TN and δ15N values in the external litterfall samples were reliable, and PLSR can be used for future prediction.

Quantitative assessment of hemodynamic and structural characteristics of in vivo brain tissue using total diffuse reflectance spectrum measured in a non-contact fashion.

Here we present a new methodology that investigates the intrinsic structural and hemodynamic characteristics of in vivo brain tissue, in a non-contact fashion, and can be easily incorporated in an intra-operative environment. Within this methodology, relative total diffuse reflectance spectra (RTD(λ)) were acquired from targets using a hybrid spectroscopy imaging system. A spectral interpretation algorithm was subsequently applied to RTD(λ) to retrieve optical properties related to the compositional and structural characteristics of each target. Estimation errors of the proposed methodology were computationally evaluated using a Monte Carlo simulation model for photon migration under various conditions. It was discovered that this new methodology could handle moderate noise and achieve very high accuracy, but only if the refractive index of the target is known. The accuracy of the technique was also validated using a series of tissue phantom studies, and consistent and accurate estimates of μs'(λ)/μa(λ) were obtained from all the phantoms tested. Finally, a small-scale animal study was conducted to demonstrate the clinical utility of the reported method, wherein a forepaw stimulation model was utilized to induce transient hemodynamic responses in somatosensory cortices. With this approach, significant stimulation-related changes (p < 0.001) in cortical hemodynamic and structural characteristics were successfully measured.

Variegation and red abaxial epidermis define the leaf optical properties of Cyclamen purpurascens

Cyclamen purpurascens originates from the forest understorey and has variegated leaves and red abaxial epidermis. We measured the morphological and biochemical traits, and reflectance and transmittance spectra of leaves of C. purpurascens sampled through the growing season. We determined the optical properties and differences between the light-green and dark-green sections of the variegated leaves, and investigated the role of the red abaxial epidermis. The light-green leaf sections contained lower contents of chlorophyll a and b, carotenoids (in all samples) and anthocyanins (in April only) per leaf area, compared to the dark-green leaf sections, although the ratios of chlorophyll a to b and carotenoids to total chlorophyll were the same, except in April. During the closing of the canopy, chlorophyll a and b contents increased, while contents of carotenoids and anthocyanins decreased, as did the chlorophyll a/b and carotenoid/total chlorophyll ratios. The optical properties of the leaves in February showed high reflectance for UV and violet radiation, and low reflectance for near infrared radiation, for both types of leaf sections. The transmittance spectra for leaves without the red anthocyanic epidermis showed a pronounced peak from 520nm to 625nm, and enhancement in the near infrared region. The relative reflectance spectra of the red and colourless abaxial epidermis alone differed only in the green and yellow range. The relative transmittance of the red abaxial epidermis was significantly lower than for the colourless epidermis over the entire spectral range. Decreased transmittance in the green and yellow was obtained only for the red coloured abaxial epidermis. The variability of transmittance spectra during the season is best explained by the levels of chlorophyll b, carotenoids and anthocyanins. Our data reveal the importance of these pigments in leaf variegation, and particularly of the red abaxial anthocyanic epidermis for absorbing light in the green, yellow and near infrared.

Constraints on iron sulfate and iron oxide mineralogy from ChemCam visible/near-infrared reflectance spectroscopy of Mt. Sharp basal units, Gale Crater, Mars

Relative reflectace point spectra (400–840 nm) were acquired by the Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory (MSL) rover Curiosity in passive mode (no laser) of drill tailings and broken rock fragments near the rover as it entered the lower reaches of Mt. Sharp and of landforms at distances of 2–8 km. Freshly disturbed surfaces are less subject to the spectral masking effects of dust, and revealed spectral features consistent with the presence of iron oxides and ferric sulfates. We present the first detection on Mars of a ~433 nm absorption band consistent with small abundances of ferric sulfates, corroborated by jarosite detections by the Chemistry and Mineralogy (CheMin) X-ray diffraction instrument in the Mojave, Telegraph Peak, and Confidence Hills drilled samples. Disturbed materials near the Bonanza King region also exhibited strong 433 nm bands and negative near-infrared spectral slopes consistent with jarosite. ChemCam passive spectra of the Confidence Hills and Mojave drill tailings showed features suggestive of the crystalline hematite identified by CheMin analyses. The Windjana drill sample tailings exhibited flat, low relative reflectance spectra, explained by the occurrence of magnetite detected by CheMin. Passive spectra of Bonanza King were similar, suggesting the presence of spectrally dark and neutral minerals such as magnetite. Long-distance spectra of the “Hematite Ridge” feature (3–5 km from the rover) exhibited features consistent with crystalline hematite. The Bagnold dune field north of the Hematite Ridge area exhibited low relative reflectance and near-infrared features indicative of basaltic materials (olivine, pyroxene). Light-toned layers south of Hematite Ridge lacked distinct spectral features in the 400–840 nm region, and may represent portions of nearby clay minerals and sulfates mapped with orbital near-infrared observations. The presence of ferric sulfates such as jarosite in the drill tailings suggests a relatively acidic environment, likely associated with flow of iron-bearing fluids, associated oxidation, and/or hydrothermal leaching of sedimentary rocks. Combined with other remote sensing data sets, mineralogical constraints from ChemCam passive spectra will continue to play an important role in interpreting the mineralogy and composition of materials encountered as Curiosity traverses further south within the basal layers of the Mt. Sharp complex.

Linear spectropolarimetry: a new diagnostic tool for the classification and characterization of asteroids

Abstract We explore the use of spectropolarimetry as a remote sensing tool for asteroids in addition to traditional reflectance measurements. In particular, we are interested in possible relationships between the wavelength-dependent variation of linear polarization and the properties of the surfaces, including albedo and composition. We have obtained optical spectropolarimetric measurements of a dozen asteroids of different albedo and taxonomic classes and of two small regions at the limb of the Moon. We found that objects with marginally different relative reflectance spectra (in the optical) may have totally different polarization spectra. This suggests that spectropolarimetry may be used to refine the classification of asteroids. We also found that in some cases the Umov law may be violated, that is, in contrast to what is expected from basic physical considerations, the fraction of linear polarization and the reflectance may be positively correlated. In agreement with a few previous studies based on multicolour broad-band polarimetry, we found that the variation of linear polarization with wavelength and with phase-angle is correlated with the albedo and taxonomic class of the objects. Finally, we have serendipitously discovered that spinel-rich asteroid (599) Luisa, located very close to the Watsonia family, is a member of the rare class of Barbarian asteroids. We suggest that future modelling attempts of the surface structure of asteroids should be aimed at explaining both reflectance and polarization spectra.

Scattered light correction of Hayabusa/AMICA data and quantitative spectral comparisons of Itokawa

Abstract The Hayabusa spacecraft rendezvoused with its target asteroid 25143 Itokawa in 2005 and brought an asteroidal sample back to the Earth in 2010. The onboard camera, AMICA, took more than 1400 images of Itokawa during the rendezvous phase. It was reported that the AMICA images were severely contaminated by light scatter inside the optics. The effect made it difficult to produce the color maps at longer wavelengths (&amp;gt; 800 nm). In this paper, we demonstrate a method to subtract the scattered light by investigating the dim halos of Itokawa and the Moon taken by AMICA during the inflight operation. As a result, we found that the overall data reduction scheme including the scattered light correction enables the recognition of 3% regional differences in the relative reflectance spectra of Itokawa. We confirmed that the color variation in Itokawa was largely attributed to space weathering.

ChemCam passive reflectance spectroscopy of surface materials at the Curiosity landing site, Mars

The spectrometers on the Mars Science Laboratory (MSL) ChemCam instrument were used in passive mode to record visible/near-infrared (400–840nm) radiance from the martian surface. Using the onboard ChemCam calibration targets’ housing as a reflectance standard, we developed methods to collect, calibrate, and reduce radiance observations to relative reflectance. Such measurements accurately reproduce the known reflectance spectra of other calibration targets on the rover, and represent the highest spatial resolution (0.65mrad) and spectral sampling (<1nm) visible/near-infrared reflectance spectra from a landed platform on Mars. Relative reflectance spectra of surface rocks and soils match those from orbital observations and multispectral data from the MSL Mastcam camera. Preliminary analyses of the band depths, spectral slopes, and reflectance ratios of the more than 2000 spectra taken during the first year of MSL operations demonstrate at least six spectral classes of materials distinguished by variations in ferrous and ferric components. Initial comparisons of ChemCam spectra to laboratory spectra of minerals and Mars analog materials demonstrate similarities with palagonitic soils and indications of orthopyroxene in some dark rocks. Magnesium-rich “raised ridges” tend to exhibit distinct near-infrared slopes. The ferric absorption downturn typically found for martian materials at <600nm is greatly subdued in brushed rocks and drill tailings, consistent with their more ferrous nature. Calcium-sulfate veins exhibit the highest relative reflectances observed, but are still relatively red owing to the effects of residual dust. Such dust is overall less prominent on rocks sampled within the “blast zone” immediately surrounding the landing site. These samples were likely affected by the landing thrusters, which partially removed the ubiquitous dust coatings. Increased dust coatings on the calibration targets during the first year of the mission were documented by the ChemCam passive measurements as well. Ongoing efforts to model and correct for this dust component should improve calibration of the relative reflectance spectra. This will be useful as additional measurements are acquired during the rover’s future examinations of hematite-, sulfate-, and phyllosilicate-bearing materials near the base of Mt. Sharp that are spectrally active in the 400–840nm region.

Detection of large color variation in the potentially hazardous asteroid (297274) 1996 SK

Low-inclination near-earth asteroid (NEA) (297274) 1996 SK, which is also classified as a potentially hazardous asteroid, has a highly eccentric orbit. It was studied by multi-wavelength photometry within the framework of an NEA color survey at Lulin Observatory. Here, we report the finding of large color variation across the surface of (297274) 1996 SK within one asteroidal rotation period of 4.656 ± 0.122 hours and classify it as an S-type asteroid according to its average colors of B — V = 0.767 ± 0.033, V — R = 0.482 ± 0.021, V — I = 0.801 ± 0.025 and the corresponding relative reflectance spectrum. These results might be indicative of differential space weathering or compositional inhomogeneity in the surface materials.

The Processing and Classification for the Spectra of Six Comets

In order to explore the relationship between comets and asteroids, the spectra of six comets, including 78P, C/2009 P1, 49P, C/2010 G2, C/2010 S1, and C/2011 F1, have been observed with the 2.16 m telescope at the Xinglong Observing Station of National Astronomical Observatories. At the same time, the spectra of some sun-like stars are also observed. The IRAF (Image Reduction and Analysis Facility) software is used to process the obtained spectra, and to obtain the relative reflectance spectra of the six comets. Then, they are compared with the 24 asteroid spectral types of the Bus-DeMeo taxonomy to derive the spectral distances of these comets. According to the order of the calculated spectral distances, the details of the reflectance spectra, as well as the results of the K-S test, the asteroid spectral types which are most close to the spectra of these comets are finally determined.

Lattice constants and optical response of pseudomorph Si-rich SiGe:B

Pseudomorph epitaxial films of Si1−xGex:B were grown on undoped (100) Si for x ≤ 0.026 and the B concentration of 1.3 × 1020 cm−3.The in-plane and out-of-plane lattice constants were determined using the X-ray techniques for 004 symmetric and 224 asymmetric diffraction. The influence of B and Ge co-doping has been detected in reflectance and ellipsometric spectra from infrared to ultraviolet. Free-hole plasma and Fano-type resonances of Si phonons and localized 11B and 10B vibrations have been observed. The spectral shift of E1 electronic transitions has been quantified. We found a simple way to test the variations of Ge content using relative reflectance spectra.

A multispectral vision system to evaluate enzymatic browning in fresh-cut apple slices

The main objective of this study was to develop a vision system that is able to classify fresh-cut apple slices according to the development of enzymatic browning. The experiment was carried out on ‘Granny Smith’ apple slices stored at 7.5 °C for 9 days ( n = 120). Twenty-four samples were analyzed per day: at zero time and after storage for 1, 3, 7 and 9 days, which corresponds to treatments t 0, t 1, t 3, t 7 and t 9 respectively. Multispectral images were acquired from the samples by employing a 3-CCD camera centered at the infrared (IR, 800 nm), red (R, 680 nm) and blue (B, 450 nm) wavelengths. Apple slices were evaluated visually according to a visual color scale of 1–5 (where 1 corresponds to fresh samples without any browning and 5 to samples with severe discoloration), to obtain a sensory evaluation index ( I SE ) for each sample. Finally, for each sample and for each treatment, visible (VIS) relative reflectance spectra (360–740 nm) were obtained. In order to identify the most related wavelengths to enzymatic browning evolution, unsupervised pattern recognition analysis of VIS reflectance spectra was performed by principal components analysis (PCA) on the autoscaled data. Maximum loading values corresponding to the B and R areas were observed. Therefore, a classification procedure was applied to the relative histograms of the following monochromatic images (virtual images), which were computed pixel by pixel: (R − B)/(R + B), R − B and B/R. In all cases, a non-supervised classification procedure was able to generate three image-based browning reference classes (BRC): Cluster A (corresponding to the t 0 samples), Cluster B ( t 1 and t 3 samples) and Cluster C ( t 7 and t 9 samples). An internal and an external validation ( n = 120) were carried out, and the best classifications were obtained with the (R − B)/(R + B) and B/R image histograms (internal validation: 99.2% of samples correctly classified for both virtual images; external validation: 84% with (R − B)/(R + B) and 81% with B/R). The camera classification was evaluated according to the colorimetric measurements, which were usually utilized to evaluate enzymatic browning development (CIE L* a* b* color parameters and browning index, BI) and according to I SE . For both validation phases a*, b*, BI and I SE increased while L* values decreased with image-based class number, thereby reflecting their browning state.

ESO large program about transneptunian objects: surface variations on (47171) 1999 TC36

Aims. We investigate the surface composition of the Plutino (47171) 1999 TC36. Methods. We completed near-infrared photometric and spectroscopic observations of (47171) 1999 TC36 with the adaptive optics instrument NACO at the ESO VLT during 12 October 2006, and present these data with ISAAC and SINFONI spectroscopic observations carried out about one month later on 9 November 2006 and 8 November 2006, respectively. The ISAAC and SINFONI spectroscopic observations were combined with a visible spectrum obtained by FORS1 on 9 November 2006. Composition and properties of the compounds present on the surface of the target are investigated by applying a Hapke radiative transfer model to the measured spectra and to previously published observations. Results. We present the relative reflectance spectrum of (47171) 1999 TC36 in the wavelength range (0.37–2.33) μm. An intimate mixture of Triton tholin, Titan tholin, serpentine, and Triton tholin diluted in water ice represents the best-fit model description of the measured spectrum. Any significant differences from the published spectra of (47171) 1999 TC36 taken on 2001 and 2003 could be due to surface heterogeneity.

Radiative transfer modeling of lunar highlands spectral classes and relationship to lunar samples

Tompkins and Pieters (1999) identified eleven spectral classes present on the surface of the Moon. Here we model these spectral classes to determine the compositions that define them. We do this by mathematically matching spectral classes to radiative transfer computed spectra using spectral shape, contrast, and excursion parameters as defining characteristics. Model spectra are based upon known mineralogies, mafic‐mineral Mg′s (molar (Mg/(Mg + Fe)) · 100), and maturities. We compare these compositional results to a compilation of ∼100 Apollo samples to determine plausible representative samples for these spectra. Results indicate that unique mineralogic solutions for several spectral classes can be determined unambiguously; however, classes previously interpreted to be pyroxene‐rich are compositionally ambiguous. Results suggest these ambiguous mineral assemblages are not random, but correlate with variations in absolute reflectance. These data further suggest absolute reflectance is a compositionally diagnostic spectral parameter that should be used in conjunction with relative reflectance analysis to constrain mineralogy. Although absolute reflectance for the eleven spectral classes is not available to constrain their composition, we detail mineral, chemical (i.e., Mg′), and absolute reflectance variations of matching model relative reflectance spectra to narrow the possibilities. This information is used in a pilot study of Bullialdus crater, for which Clementine absolute reflectance is known. Results indicate Bullialdus's central peak consists of Tompkins and Pieters' spectral classes AN, AGN, and N. Bullialdus's spectra that match class N are roughly consistent with previous compositional interpretations; however, matches to classes AN and AGN indicate more mafic assemblages typical of Mg‐suite norite/gabbronorite rocks.

Crystallinity and temperature of icy grains in comet C/2002 T7 (LINEAR)

We discuss the crystallinity and the temperature of water ice grains in the coma of comet C/2002 T7 (LINEAR) at 3.5 AU from the Sun. The observed relative reflectance spectrum in J and H bands can be reproduced by using the Hapke’s model. Due to limited S/ N ratios of the observed spectrum, however, we can not identify the phase (crystalline or amorphous states) of water ice. Both crystalline and amorphous water ices can explain the observed spectrum within the errors. If the water ice was in amorphous state, the cometary ices formed and/or condensed in the molecular cloud or in the solar nebula (at further than 25 AU from the Sun). In contrast, if the cometary water ice was in crystalline state, the temperature of the icy grains in the coma could be estimated to be about 140–170 K, which is consistent with the temperature of sublimating dirty water ice grains at 3.5 AU.

Effects of leaf age and psyllid damage on the spectral reflectance properties of Eucalyptus saligna foliage

Leaf chlorophyll content is influenced directly by many environmental stress factors. Because leaf pigment absorption is wavelength dependent, numerous narrow-band reflectance-based indices have been proposed as a means of assessing foliar health and condition. Chlorophyll content, however, also varies with leaf developmental stage. In this study, a range of morphological and physiological traits including insect damage, relative chlorophyll content (SPAD values), chlorophyll fluorescence (Fv/Fm) and reflectance spectra was measured of leaves sampled from mature Eucalyptus saligna. Relative differences among three leaf-age cohorts were compared with differences obtained from mature leaves that were either healthy or infested with the psyllid Glycaspis baileyi. Differences in relative chlorophyll content were greater between immature and mature foliage than between damaged and healthy mature leaves. These differences were confirmed in the comparisons of reflectance spectra and indices. As many eucalypt species have opportunistic crown phenology and long-lived leaves, leaf-age composition of crowns needs to be taken into account when applying reflectance-based indices to assess foliar condition of eucalypts.

Interface Effects on Magneto-Optic Kerr and Reflectivity Spectra in Ultrathin Fe/Au and Fe/Ag Systems

Molecular beam epitaxy grown Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au and Ag/Fe (t)/Ag sandwiches on MgO (001) substrates were investigated by means of classical and magneto-optic (MO) Kerr ellipsometry and relative reflectance spectroscopy at photon energies between 1.5 and 6 eV. The layer thickness t varied between 1.0 and 2.5nm for Au spacer and between 0.8 and 1.8nm for Fe. The MO polar and longitudinal Kerr effect spectra in Ag/Fe (t)/Ag can be explained using a single off-diagonal permittivity tensor element. This is not the case in Au/Fe (t)/Au, Au/Fe/Au (t)/Fe/Au. Deviations of the longitudinal spectra from the model indicate the anisotropy in the permittivity tensor and are assigned to an Fe-Au interface layer of reduced symmetry. The interface effect, observed between 3 and 4.2 eV, is best resolved in Au/Fe/Au (t)/Fe/Au, but can also be seen on Au/Fe (t)/Au. The relative reflectance spectra in Au/Fe/Au (t)/Fe/Au with an Au reference reflector show a narrowing of the Au peak centered at the photon energy of 3.5 eV. It is proposed that the narrowing is induced by adjacent Fe layer with in-plane magnetization.

Dust deposition at the Mars Pathfinder landing site: observations and modeling of visible/near-infrared spectra

Temporal variations in the visible/near-infrared reflectance spectra of the radiometric calibration targets on the Mars Pathfinder (MPF) lander obtained by the Imager for Mars Pathfinder (IMP) camera reveal the effects of aeolian dust deposition at the MPF site throughout the mission. Sky brightness models in combination with two-layer radiative transfer models were used with these data to track changes in dust opacity on the radiometric calibration targets (RCTs) to constrain the dust deposition rate and the spectral properties of the deposited dust. Two-layer models were run assuming both linear and nonlinear dust accumulation rates, and suggest that RCT dust optical depth at the end of the 83-sol mission was 0.08 to 0.16, or on the order of 5- to 10-μm thickness for plausible values for dust porosity and grain size. These values correspond to dust fall rates of about 20–45 μm per Earth year, consistent with previous studies of dust deposition on Mars. The single scattering albedos of the dust derived from the models fall between those previously determined for atmospheric dust and bright soils. Comparisons of relative reflectance spectra calibrated using observed RCT radiances from late in the mission versus using radiances from modeled (dust-free) RCTs also reveal distinct spectral differences consistent with dust on the RCTs. Temporal variations in RCT dust opacity are not clearly linked to known passages of vortices at the MPF site, but overall suggest that deposition of dust onto the targets by local dust devils may be favored over erosion. Analyses of temporal changes in visible/near-infrared spectra will provide valuable information for future missions by constraining how dust deposition affects landed spacecraft operability (e.g., solar power availability), instrument calibration, and interpretations of surface mineralogy and composition.

Observations of 2000 DP 107 in NAOC: rotation period and reflectance spectrum

Photometric observations of a Near-Earth-Asteroid (NEA) 2000 DP 107 were made on four successive nights during October 2000, 1.4–4.7 with the 0.6-m/0.9-m Schmidt telescope of National Astronomical Observatories, CAS (NAOC). The derived rotation period of 0.1156 day was consistent with that obtained by Pravec et al. (IAU Circular No. 7504, 2000). In addition, the relative reflectance spectrum of the asteroid covering 0.35– 0.9 μm was obtained with the NAOC 2.16-m telescope adopting a low-resolution grating ( 10 A ̊ /pix) on October 2, 2000, which revealed that 2000 DP 107 is an M-type asteroid.