High-resolution Reflectance Spectra Research Articles

Visible and near-infrared spectral results of Chang’E-5 surficial and subsurface soils

Aims. Studies on high-resolution and high-precision laboratory reflectance spectra of the Moon have historically been restricted to the analysis of old Apollo samples (>3.0 Ga). In contrast, studies of young lunar soils have exclusively relied on the analysis of remote sensing spectra. In this study, we present the results of a laboratory spectral investigation of young lunar soils (~2.0 Ga) obtained by the Chang’E-5 (CE-5) mission. Methods. We analyzed surficial and subsurface soils collected through scooped and drilled sampling methods. The laboratory reflectance spectra of the CE-5 soils were compared with those of Apollo soils and orbital spectra. Two methods were employed for maturity inversion. The relationship between the UV-vis color and TiO2 content of young basalts was also investigated. Results. The CE-5 samples exhibit much fresher spectral features, including higher reflectance, deeper absorption depths, and a smaller visible and near-infrared continuum slope (VNCS), compared to pristine regolith. The subsurface soils sampled from a depth of approximately 10 cm exhibit a slightly fresher spectral feature compared to the surficial soils. Our comparison revealed a rapid rate of space weathering at the lunar surface compared to the vertical overturn. Compared to older iron-rich soils, the CE-5 soils have a larger reflectance but similar UV-vis ratios. The UV-vis ratio alone could not accurately predict the TiO2 content of all mare basalts. The CE-5 samples provide a new ground truth for estimating the TiO2 content of young lunar basalts, which have the largest uncertainty in TiO2 content, as estimated from spectral parameters. We find that the samples returned by the CE-5 mission represent disturbed soils and that they exhibit significantly fresher characteristics compared to pristine regolith, a fact that should be kept in mind when using samples as ground truth for remote sensing research.

Miniatured Fabry-Perot strain probe based on anti-resonant hollow core fiber

A novel miniature Fabry-Perot strain probe based on anti-resonant hollow core fiber (ARHCF) is proposed and experimentally demonstrated, which is fabricated by sandwiching a ARHCF between a single-mode fiber (SMF) and a multi-mode fiber (MMF). Two fusion points of the three optical fibers have been worked as mirrors to form a Fabry-Perot interferometer (FPI). The experimental results agree well with the simulation results. The ARHCF differs from the previous hollow core fiber (HCF) by obtaining high-resolution reflection spectra even when the air hole collapses during fiber fusion. By taking advantage of the insensitivity of ARCHF to temperature and refractive index (RI), the FPI is made small enough to work in tight spaces with high temperature (up to 1000 ℃) and humidity, which is unmatched by some previous transmissive strain sensors that are subject to multiparameter cross-sensitivity. This sensor provides new strategies and ideas for the development of strain sensors.

High-resolution spectral models of TRAPPIST-1e seen as a Pale Blue Dot for ELT and JWST observations

ABSTRACT Rocky exoplanets orbiting in the habitable zone (HZ) of nearby M dwarfs provide unique opportunities for characterizing their atmospheres and searching for biosignature gases. TRAPPIST-1e, a temperate Earth-sized exoplanet in the HZ of a nearby M dwarf, is arguably the most favourable target for ground- and space-based atmospheric characterization by the extremely large telescopes (ELTs) and the James Webb Space Telescope. To inform future observations in reflected and emitted lights using these upcoming telescopes, we simulate the high-resolution reflection and emission spectra for TRAPPIST-1e for both modern and prebiotic Earth-like atmospheric compositions. To demonstrate the effects of wavelength-dependent albedo on climate and spectra, we further simulate five albedo scenarios for each atmospheric composition: cloudy modern Earth-like, cloud-free modern Earth-like, cloudy ocean planet, 100 per cent cloudy planet, and wavelength-independent albedo of 0.31. We use the recent Mega-MUSCLES spectral energy distribution of TRAPPIST-1 for our models. We show that the O2 + CH4 and O3 + CH4 biosignature pairs as well as climate indicators (CO2 and H2O) show features in both high-resolution reflection and emission spectra of TRAPPIST-1e that the ELTs can search for. Our high-resolution data base for modern and prebiotic Earth TRAPPIST-1e models with various surface compositions and cloud distributions provides a tool for observers to train retrieval algorithms and plan observation strategies to characterize this potentially habitable world.

Detection mechanism and instrument characteristics of the Mars Mineralogical Spectrometer for the Tianwen-1 orbiter

<p indent="0mm">The Mars Mineralogical Spectrometer (MMS) is the hyperspectral imager <sc>(0.379–1.076 μm</sc> at 2.73 nm/band, <sc>1.033–3.425 μm</sc> at 7.5 nm/band) on China’s first Mars exploration mission, the Tianwen-1 Mars Orbiter. In an elliptical orbit, MMS uses far-fire point calibration and near-fire point push-broom imaging to obtain spectral and spatial information on the surface of Mars. MMS can obtain visible and infrared images with high-resolution reflectance spectra of the key areas of the Martian surface and can map the global surface using its multispectral mode. It is equipped with the option of performing continuous spectral sampling and interval sampling of the entire spectrum. Additionally, it has the ability to perform in-flight calibration. The article introduces the instrument’s structure and detection principle, as well as conducts laboratory calibration and ground verification to show that the instrument meets the detection requirements. Planetary scientists will utilize MMS to acquire spectral data from the surface of Mars and evaluate the types, contents, and geographic distribution of minerals on the surface of Mars, providing critical support for elucidating the evolution of Mars.

Erratum: High-resolution reflection spectra for Proxima b and Trappist-1e models for ELT observations

Erratum: High-resolution reflection spectra for Proxima b and Trappist-1e models for ELT observations

Fine-Grained Oil Types Identification Based on Reflectance Spectrum: Implication for the Requirements on the Spectral Resolution of Hyperspectral Remote Sensors

Effectively obtaining the information about the types of oil pollutants in a spill event can help determine the source of spill and formulate the plan of emergency responses. Researchers have reported the feasibility of fine-grained oil types identification using reflectance spectra, but its requirements on spectra resolution were seldom considered. To answer this question, this study examined the oil types identification accuracies using the reflection spectra with different number of bands. The reflectance spectra of various types of oil samples were collected with a high-resolution hyperspectral remote sensor, and then resampled to coarser spectral resolution. Some of the coarse-resolution spectra were built based on the central wavelengths of AVIRIS and Landsat 8 in visible bands, so as to evaluates the potential of fine-grained oil types identification using these sensors. Three kinds of machine learning algorithms were introduced as the classifier. The identification results using the reflection spectra at different resolution showed that the machine learning models could identify oil types based on high-resolution reflectance spectra. In term of the spectra at coarser resolution, the models were still able to provide accurate predictions until the number of bands was reduced to about 16 in the visible range. Therefore, the high-resolution hyperspectral sensors (e.g., AVIRIS) have the potential of fine-grained oil types identification, but that may not be accomplished by satellite-based hyperspectral sensors with less than 4 visible bands.

In English

In this paper, we investigated high-resolution IR absorption and reflection spectra in one-sided periodical 2D macroporous silicon structures with nano-coatings of SiO2 and CdS, ZnO nanoparticles, as well as two-sided structures of macroporous silicon without nano-coatings. After changing the resolution of spectra measurements from 2 to 1 cm–1, the oscillation period of Wannier-Stark electro-optical effect decreases by 3 times, and absorption increases by 60–100 times; and for two-sided structures the oscillation period decreases by 1.5 times and absorption increases by 25–30 %. In addition, giant absorption oscillations with positive and negative amplitudes of 107 arb. un. were evaluated in spectral regions of Si–Si–bonds and Pb centers. Similar oscillations in the reflection spectra have much less amplitudes up to 4·104 arb. un. In the spectral area of the transverse phonon ωTO (Si–Si–bonds) absorption spectra of 2D macroporous silicon structures consistent fully with data for phonon polaritons in microresonators as a result of resonance interaction of dipole-active vibrations with the frequency of ωTO in thin films with the surface modes of microresonator. In addition, microresonators interact both with each other in one-sided macroporous silicon structures and in the system of two-sided macroporous silicon. The giant absorption oscillations testify the strong interaction of surface polaritons with photons. The coherence of oscillations and large-scale spatial correlation are а result of exciton-polariton condensation on macropores as microresonators. In 2D macroporous silicon structures with nano-coatings band bending on the surface of the macropores are significant. Therefore, the generated photoelectrons link with holes, forming electron-hole pairs named as exciton-polaritons according to phenomenon of Bose-Einstein condensation.

High-resolution Spectra for a Wide Range of Habitable Zone Planets around Sun-like Stars

Abstract The search for life in the universe is currently focused on Earth-analog planets. However, we should be prepared to find a diversity of terrestrial exoplanets not only in terms of host star but also in terms of surface environment. Simulated high-resolution spectra of habitable planets covering a wide parameter space are essential in training retrieval tools, optimizing observing strategies, and interpreting upcoming observations. Ground-based extremely large telescopes like ELT, GMT, and TMT and future space-based mission concepts like Origins, HabEx, and LUVOIR are designed to have the capability of characterizing a variety of potentially habitable worlds. Some of these telescopes will use high-precision radial velocity techniques to obtain the required high-resolution spectra (R ≈ 100,000) needed to characterize potentially habitable exoplanets. Here we present a database of high-resolution (0.01 cm−1) reflection and emission spectra for simulated exoplanets with a wide range of surfaces, receiving similar irradiation as Earth around 12 different host stars from F0 to K7. Depending on surface type and host star, we show differences in spectral feature strength as well as overall reflectance, emission, and star-to-planet contrast ratio of terrestrial planets in the habitable zone of their host stars. Accounting for the wavelength-dependent interaction of the stellar flux and the surface will help identify the best targets for upcoming spectral observations in the visible and infrared. All of our spectra and model profiles are available online.

High-resolution reflection spectra for Proxima b and Trappist-1e models for ELT observations

ABSTRACT The closest stars that harbor potentially habitable planets are cool M-stars. Upcoming ground- and space-based telescopes will be able to search the atmosphere of such planets for a range of chemicals. To facilitate this search and to inform upcoming observations, we model the high-resolution reflection spectra of two of the closest potentially habitable exoplanets for a range of terrestrial atmospheres and surface pressures for active and inactive phases of their host stars for both oxic and anoxic conditions: Proxima b, the closest potentially habitable exoplanet, and Trappist-1e, one of 3 Earth-size planets orbiting in the Habitable Zone of Trappist-1. We find that atmospheric spectral features, including biosignatures like O2 in combination with a reduced gas like CH4 for oxic atmospheres, as well as climate indicators like CO2 and H2O for all atmospheres, show absorption features in the spectra of Proxima b and Trappist-1e models. However for some features like oxygen, high-resolution observations will be critical to identify them in a planet's reflected flux. Thus these two planets will be among the best targets for upcoming observations of potential Earth-like planets in reflected light with planned Extremely Large Telescopes.

Fatigue Performance of Type I Fibre Bragg Grating Strain Sensors.

Although fibre Bragg gratings (FBGs) offer obvious potential for use in high-density, high-strain sensing applications, the adoption of this technology in the historically conservative aerospace industry has been slow. There are several contributing factors, one of which is variability in the reported performance of these sensors in harsh and fatigue prone environments. This paper reports on a comparative evaluation of the fatigue performance of FBG sensors written according to the same specifications using three different grating manufacturing processes: sensors written in stripped and re-coated fibres, sensors written during the fibre draw process and sensors written through fibre coating. Fatigue cycling of the fibres is provided by a customized electro-dynamically actuated loading assembly designed to provide high frequency and amplitude loading. Pre- and post-fatigue microscopic analysis and high-resolution transmission and reflection spectra scanning are conducted to investigate the fatigue performance of FBGs, the failure regions of fibres as well as any fatigue-related effects on the spectral profiles. It was found that because of the unique fabrication method, the sensors written through the fibre coating, also known as trans-jacket FBGs, show better fatigue performance than stripped and re-coated FBGs with greater control possible to tailor the optical reflection properties compared to gratings written in the draw tower. This emerging method for inscription of Type I gratings opens up the potential for mass production of higher reflectivity, apodised sensors with dense or complex array architectures which can be adopted as sensors for harsh environments such as in defence and aerospace industries.

Spectral characteristics of pine needles at the limit of tree growth in subarctic Finland

Background: Forests in subarctic regions inhabit the transitional zone between the temperate region and the Arctic, where plant survival depends on the capability of individuals to adjust to changing environments. This transitional zone, generally falling between 50° N and 70° N, is becoming increasingly vulnerable under a changing climate, with treelines moving further north and also higher up slopes. Aims: The current study was carried out at 68° N, the most sensitive zone of the subarctic and northern limit of tree growth in Finnish Lapland. The physiology of trees in these conditions is still not fully understood, and an attempt is made here to contribute to a better understanding of the functionality of leaves by studying the spectral characteristics of needles of Pinus sylvestris along an altitudinal transect. Methods: A variety of spectral indices derived from high-resolution reflectance spectra were measured on freshly excised pine needles. The specific hypothesis is that spectral reflectance data can detect the stress that pine needles suffer at high elevations. We also wish to know which of the several possible indices is most indicative of stress. Results: All of the spectral indices, with the exception of NDVI, showed elevational as well as age-related trends consistent with the hypothesis that needles from the highest elevation suffer degradation of chlorophyll. Conclusions: We conclude that appropriate reflectance measurements provide useful information that may in future be used to detect stress effects on conifer foliage. The visual appearance of trees included in the study did also reflect in their spectral characteristics.

Classifying cultivars of rice (Oryza sativa L.) based on corrected canopy reflectance spectra data using the orthogonal projections to latent structures (O-PLS) method

To improve the accuracy in discriminating plant species or genotypes in the field with canopy spectral data, a number of statistical methods incorporating measurement techniques have been developed. This study analyzed canopy reflectance spectra collected at the booting stage by using partial least square regression in combination with discriminant analysis (PLS-DA) to establish a classification model for the discrimination of three mega rice cultivars. To improve the model's capability to interpret and sharpen the separation between cultivars, PLS-DA was combined with orthogonal projection to the latent structure (O-PLS) to derive the OPLS-DA models by removing noise and the Y-orthogonal variation. The ground-based high-resolution reflectance spectra (330–1030nm) were acquired from paddy field experiments during the growing periods, and were recalculated at intervals of 10nm. With the PLS-DA approach, the total accuracy for discriminating three cultivars in the calibration datasets was 90% and was above 80% for individual cultivars. In the validation datasets, a similar capability for cultivar discrimination was obtained for both pooled and individual cultivars. However, the Y-orthogonal variation might be embedded within the PLS-DA model. Using the OPLS-DA approach, the large variation within rice cultivars (the intra variation) was effectively removed to improve the performance of both group separation and model establishment. The overall accuracy reached 100% in the calibration datasets and had superior discrimination than the PLS-DA model in the validation datasets. Therefore, the OPLS-DA method is recommended for establishing a classification model for the cultivar discrimination of rice in the vegetative phase using remotely sensed canopy reflectance spectra.

The 506 nm absorption feature in pyroxene spectra: Nature and implications for spectroscopy-based studies of pyroxene-bearing targets

High-resolution (0.34 nm) reflectance spectra of a suite of terrestrial ortho- and clinopyroxenes were characterized in the 506-nm region. This region exhibits absorption bands attributed to spin-forbidden transitions in Fe 2+ located in the M2, and possibly M1, crystallographic site(s). The most intense absorption bands (up to 3.8% deep in <45 μm fractions) are present in low Ca-content orthopyroxene spectra. This region exhibits two (spectral Group I) or more (spectral Group II) absorption bands in the 500–515 nm interval. Group I spectra are associated with the lowest Ca-content samples. For orthopyroxenes, the number of constituent absorption bands and band depths vary as a function of Ca content; increasing Ca content results the appearance of more than two absorption bands and a general reduction in band depths, offsetting an expected increase in band depth with increasing Fe 2+ content; band depths may also be reduced due to the long wavelength wing of ultraviolet region Fe–O charge transfer absorptions. Band depths and shapes in this region are also a function of grain size, with the strongest bands appearing for larger grain sizes – in the 90–250 μm range. The number and position of constituent absorption bands can be used to constrain factors such as cooling rates, as expressed in the formation of Guinier–Preston zones versus coarser-grained augite exsolution lamellae. Band depths in the spectra of fine-grained (<45 μm) clinopyroxenes do not exceed 1% and are generally lowest for spectral type A clinopyroxenes, where most of the Fe 2+ is present in the M1 crystallographic site. The appearance of the 506 nm band in the spectra of pyroxene-bearing asteroids can be used to constrain pyroxene composition and structure. The results of this study suggest that detailed analysis of absorption features in the 506 nm region is a powerful tool for determining the composition and structure of pyroxenes. The spectral resolution of the VIR-MS spectrometer aboard the Dawn spacecraft – which will examine Asteroid 4 Vesta, a body possessing surficial pyroxenes – will be sufficient to provide some constraints on pyroxene composition.

Absolute calibration of the Chang’E-1 IIM camera and its preliminary application

The interference imaging spectroradiometer (IIM) onboard the first lunar satellite of China “Chang’E-1” can now provide approximately global high spectral and spatial resolution reflectance spectra of the Moon. It is the essential instrument with which to accomplish one of the four missions of the first lunar satellite of China. As the current data provided by the Lunar Exploration Program Center and National Astronomical Observatories (NAOC) are not reflectance and the sensor response is inhomogeneous in the line direction, users can not use the current data directly. Moreover, due to the narrow band range, IIM data cannot cover the absorption peak of the mafic minerals of the Moon completely, which limits its ability for identifying minerals. The main objective of this study is to describe the methods for absolute calibration, correction and acquiring the absorption center of minerals for IIM data. The results from our study show that in the space domain the sensor response decreases toward the left, and in the spectral domain the response of the longer bands is more inhomogeneous than that of the shorter bands. After the calibration and correction, the reflectance of IIM matches the earth-based telescopic spectra well, which suggests the possible use of the processed data in the geological research. A high correlation was found between the absorption center and the wavelength at which the first derivative equals 0, i.e., the so-called Stagnation Point in the mathematical sense. In the end, we show a preliminary applied study of the two craters with diameter larger than 35 km using the calibrated data. The spectra of IIM data show that the lunar crust has compositional diversity within the km scale. Pure anorthosite may be found on the wall and floor of the Aristarchus crater with the map of absorption center, which indicates that anorthosite is ubiquitously present within the lunar crust. IIM, with its capacity to acquire lunar composition at the regional and global scale, will contribute to the research of lunar origin and evolution.

Visible near-infrared reflectance spectroscopy as a predictive indicator of soil properties

Abstract It is becoming increasingly important to improve spatial resolutions of soil maps as a fundamental information layer for studying ecological processes and to tackle land degradation. There is growing interest in the use of remote sensing technologies to assist the identification and delineation of spatial variation in soils. This paper investigates whether selected properties of extensively weathered, low fertility soils can be predicted using high-resolution reflectance spectra over the range 400–2500 nm. Clay content, carbonate concentration, organic carbon content and iron oxide content were analysed for 300 soil samples collected from the Jamestown, Belalie district, South Australia. The paper also examines the efficacy of this soil analysis methodology to supplement or replace traditional soil sampling in soil survey to increase sampling density and improve the spatial resolution of soil maps. Reflectance spectra were obtained from air-dried samples under controlled laboratory conditions using an ASD FieldSpec Pro spectroradiometer. Partial least squares regression was used to examine relationships between soil mineralogy, clay content and organic carbon and the reflectance spectra and identify the wavelengths contributing to prediction of these soil properties. Results show that it is possible to predict clay content, soil organic carbon, iron oxide content and carbonate content. Cross-validation R2 values for all analyses were above 0.5 and the residual prediction difference (RPD) was acceptable for all soil properties. Carbonate and clay content were more accurately predicted than iron oxide and organic carbon. All samples were collected from the same geographical area such that they represented physical properties over a naturally occurring range and provide a prediction that could be related to subsequent image analysis or be used to carry out local scale soil survey. A rapid and reliable form of soil mapping could be developed from this methodology.

REFLECTANCE SPECTROSCOPY FOR ROUTINE AGRONOMIC SOIL ANALYSES

Near-infrared reflectance spectroscopy is a demonstrated tool for quantitative analysis of numerous soil properties. Reported advantages include analytical precision, predictive accuracy, and reduced costs and processing times. A library (N = 1933) representing all major soil orders in Florida was assembled from samples submitted to the University of Florida Extension Soil Testing Laboratory for routine testing during 2004-2005. High-resolution diffuse reflectance spectra from each sample in the visible/near infrared were used to predict observations made using standard laboratory analytical procedures for soil pH, Mehlich-1-extractable P, K, Ca, Mg, Cu, Mn, and Zn, percentage of organic matter, and saturated hydraulic conductivity (Ksat). Calibrations were immediately applicable for organic matter and Al, based on relative performance determinant values (RPD = standard deviation/standard error of validation > 2.0). Models for pH, P, Ca, and Ksat showed moderate accuracy (1.5 < RPD < 2.0), whereas those for K, Cu, Mg, Mn, Zn, and Fe exhibited low efficiency (RPD < 1.5), indicating a need for further refinement before near-infrared reflectance spectroscopy is a viable alternate method to standard laboratory procedures. Prediction of soil fertility and productivity based on published Florida soil diagnostic categories showed effective discrimination for pH, P Mg, Mn, Cu (phytotoxicity), and Ksat. Our study showed that prediction efficiency is a strong function of mean nutrient/analyte concentration in the soil. We further demonstrated that near-infrared reflectance spectroscopy error rates were comparable to, and in some cases smaller than, laboratory analytical error rates, suggesting that the observed low spectral prediction efficiency may be substantially because of uncertainty in the laboratory data.

Evaluating Ecological Condition Using Soil Biogeochemical Parameters and Near Infrared Reflectance Spectra

Rapid, repeatable assessment of ecological condition is critical for quantitative ecosystem monitoring. Soils provide a sensitive, integrative indicator for which sampling and analysis techniques are well defined. We evaluated soil properties as indicators of ecological condition (subjectively classified into minimally/moderately/severely degraded based on vegetative, hydrologic and edaphic cues) at 526 sites within Ft. Benning military installation (Georgia, USA). For each sample, we measured 17 biogeochemical parameters, and collected high-resolution diffuse reflectance spectra using visible/near infrared reflectance spectroscopy (VNIRS). VNIR spectra have been related to numerous soil attributes - we examine them here for diagnosing integrated response (i.e., ecological condition). We used ordinal logistic regression (OLR) and classification trees (CT) to discriminate between condition categories using both sets of predictors (biogeochemistry and spectra). Sixteen biogeochemical parameters were significantly different across condition categories; however, multivariate models greatly improved discrimination ([calibration, validation] accuracy of [69%, 66%] and [96%, 73%] for OLT and CT models, respectively). Important predictors included total C, total P, and Mehlich K/Ca/Mg. VNIR spectra further improved discrimination ([calibration, validation] accuracy of [74%, 70%] and [96%, 75%] for OLR and CT models, respectively). While spectra were comparably effective at discriminating minimally degraded sites, they were significantly more effective at discriminating severely degraded sites. Error rates across confounding factors suggest that watershed of origin and landscape position were the only important confounders, likely due to imbalanced sampling. We conclude that multivariate diagnosis improves accuracy, and that VNIR spectroscopy, which yields substantial cost and logistical improvements over conventional analyses, provides an effective tool for rapid condition diagnosis.

An experimental investigation of discrete changes in pitch in a thin, planar chiral nematic device

The phenomenon whereby sudden changes in helicoidal pitch occur in thin chiral nematic devices with strong surface anchoring has been studied experimentally. This has been done with the aim of examining the underlying process in the context of existing theory. Thin devices (∼2.5 µm thick) containing two commercially available chiral nematic liquid crystals were employed in the study. The samples were chosen for their dependence of pitch on temperature; one exhibits a very slow increase in pitch with increasing temperature (95.6% of the Merck material BL131 in BL130), while the second shows the more common rapid reduction in pitch with increasing temperature (the Merck mixture TM1001). High resolution reflection spectra were obtained for the devices and a numerical fitting algorithm, based on the Berreman 4×4 matrix technique, provided accurate information on changes in the pitch, refractive indices, device thickness and changes in the surface director across the pitch jump region. We demonstrate that changes in refractive index and device thickness are negligible in analysis of the reflection spectra across the pitch jumps. We further show that the pitch changes discontinuously at the pitch jump, with no variation in its value as the process occurs. We find evidence that the surface directors also change by less than 10° during this process in a manner analogous to coiling or uncoiling a constrained spring. This mechanism differs somewhat from others proposed in the literature.

Exploring field vegetation reflectance as an indicator of soil contamination in river floodplains

This study investigated the relation between vegetation reflectance and elevated concentrations of the metals Ni, Cd, Cu, Zn and Pb in river floodplain soils. High-resolution vegetation reflectance spectra in the visible to near-infrared (400–1350 nm) were obtained using a field radiometer. The relations were evaluated using simple linear regression in combination with two spectral vegetation indices: the Difference Vegetation Index (DVI) and the Red-Edge Position (REP). In addition, a multivariate regression approach using partial least squares (PLS) regression was adopted. The three methods achieved comparable results. The best R 2 values for the relation between metals concentrations and vegetation reflectance were obtained for grass vegetation and ranged from 0.50 to 0.73. Herbaceous species displayed a larger deviation from the established relationships, resulting in lower R 2 values and larger cross-validation errors. The results corroborate the potential of hyperspectral remote sensing to contribute to the survey of elevated metal concentrations in floodplain soils under grassland using the spectral response of the vegetation as an indicator. Additional constraints will, however, have to be taken into account, as results are resolution- and location-dependent.

Vacuumultraviolet spectroscopy of excitons in solid krypton

The emission of free and self-trapped excitons in solid Kr wasinvestigated using luminescence spectroscopy in the vacuumultraviolet region. The influence of the sample crystalstructure and Xe impurity on the shape and location of theself-trapped exciton band was observed directly using samplesgrown under different conditions from gases with various degreesof purity. For the first time, the luminescence spectra weremeasured for practically Xe-free solid Kr samples of highstructural quality.New high-resolution reflection spectra of solid Kr were measuredas well. Due to the good quality of the samples and excellentvacuum conditions, a new member of the exciton series (n = 5)was revealed. On the basis of high-resolution reflectionmeasurements, more accurate values of several parametersconcerning excitons in solid Kr were determined.