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LEMONY – a library of empirical medium-resolution spectra by observations with the NAOC Xinglong 2.16-m and YNAO Gaomeigu 2.4-m telescopes
摘要： In this study, we expand the coverage and improve the homogeneity of the distribution of MILES template stars in the parameter space, as well as extend the wavelength coverage of the template spectra to the far red beyond the CaII triplet. To achieve this, we have carried out a major observational campaign using two long-slit spectrographs: the OMR mounted on the National Astronomy Observatory of China (NAOC) 2.16-m telescope and the Yunnan Faint Object Spectrograph and Camera (YFOSC) mounted on the Yunnan Astronomical Observatory (YNAO) 2.4-m telescope. The original sample is based on the MILES library, supplemented by 918 stars selected from the PASTEL data base. In total, 822 OMR and 1324 YFOSC spectra have been collected and reduced, covering the wavelength ranges λλ3800–5180 and λλ5150–9000, respectively. The spectra have a mean resolution full width at half-maximum of ～3.3 ? and are wavelength- and ?ux-calibrated to an accuracy of ～20 km s?1 and ～5 per cent, respectively. The spectra are further corrected for systematic errors in the wavelength calibration to an accuracy of ～4 km s?1 by cross-correlating with the theoretical spectra. Almost all the spectra have an average signal-to-noise ratio better than 100 per pixel. Combined with the MILES spectra, there are now 1731, 1542, 1324 and 1273 stars with spectra covering λλ3800–5180, λλ3800–7500, λλ5150–9000 and λλ3800–9000, respectively. In this paper, we describe our template star selection, the observation and data reduction, and we present the reduced spectra collected hitherto.
关键词： stars: fundamental parameters,techniques: imaging spectroscopy
更新于2025-09-19 17:15:36
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Performance of the VLT Planet Finder SPHERE
摘要： Context. The new planet finder for the Very Large Telescope (VLT), the Spectro-Polarimetric High-contrast Exoplanet REsearch (SPHERE), just had its first light in Paranal. A dedicated instrument for the direct detection of planets, SPHERE, is composed of a polarimetric camera in visible light, the Zurich IMager POLarimeter (ZIMPOL), and two near-infrared sub-systems: the Infra-Red Dual-beam Imager and Spectrograph (IRDIS), a multi-purpose camera for imaging, polarimetry, and long-slit spectroscopy, and the integral field spectrograph (IFS), an integral field spectrograph. Aims. We present the results obtained from the analysis of data taken during the laboratory integration and validation phase, after the injection of synthetic planets. Since no continuous field rotation could be performed in the laboratory, this analysis presents results obtained using reduction techniques that do not use the angular differential imaging (ADI) technique. Methods. To perform the simulations, we used the instrumental point spread function (PSF) and model spectra of L and T-type objects scaled in contrast with respect to the host star. We evaluated the expected error in astrometry and photometry as a function of the signal to noise of companions, after spectral differential imaging (SDI) reduction for IRDIS and spectral deconvolution (SD) or principal component analysis (PCA) data reductions for IFS. Results. We deduced from our analysis, for example, that β Picb, a 12 Myr old planet of ～10 MJup and semi-major axis of 9–10 AU, would be detected with IRDIS with a photometric error of 0.16 mag and with a relative astrometric position error of 1.1 mas. With IFS, we could retrieve a spectrum with error bars of about 0.15 mag on each channel and astrometric relative position error of 0.6 mas. For a fainter object such as HR 8799d, a 13 MJup planet at a distance of 27 AU, IRDIS could obtain a relative astrometric error of 3 mas.
关键词： techniques: imaging spectroscopy,planetary systems,instrumentation: spectrographs,methods: data analysis,instrumentation: high angular resolution
更新于2025-09-19 17:15:36
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Capability of Spaceborne Hyperspectral EnMAP Mission for Mapping Fractional Cover for Soil Erosion Modeling
摘要： Soil erosion can be linked to relative fractional cover of photosynthetic-active vegetation (PV), non-photosynthetic-active vegetation (NPV) and bare soil (BS), which can be integrated into erosion models as the cover-management C-factor. This study investigates the capability of EnMAP imagery to map fractional cover in a region near San Jose, Costa Rica, characterized by spatially extensive coffee plantations and grazing in a mountainous terrain. Simulated EnMAP imagery is based on airborne hyperspectral HyMap data. Fractional cover estimates are derived in an automated fashion by extracting image endmembers to be used with a Multiple End-member Spectral Mixture Analysis approach. The C-factor is calculated based on the fractional cover estimates determined independently for EnMAP and HyMap. Results demonstrate that with EnMAP imagery it is possible to extract quality endmember classes with important spectral features related to PV, NPV and soil, and be able to estimate relative cover fractions. This spectral information is critical to separate BS and NPV which greatly can impact the C-factor derivation. From a regional perspective, we can use EnMAP to provide good fractional cover estimates that can be integrated into soil erosion modeling.
关键词： EnMAP,Costa Rica,imaging spectroscopy,soil erosion modeling,spectral mixture analysis
更新于2025-09-19 17:15:36
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Imaging Spectroscopy of Forest Ecosystems: Perspectives for the Use of Space-borne Hyperspectral Earth Observation Systems
摘要： The emerging challenges in preserving and managing forest ecosystems are multiscale in terms of space and time, and therefore require spatially and temporally contiguous information sources. Imaging spectroscopy has the potential to contribute information that cannot be raised by other Earth Observation Systems. In particular, the spectral capacity to monitor the distributions of chemical traits, such as canopy foliar nitrogen distribution, and to track changes in water content or the percentage water in plants, has already opened novel pathways toward assessing the global variability of ecosystem functions and services. However, there is an ongoing debate on how to best extract this type of information from the spectral measurements. Empirical approaches have demonstrated their efficiency in a multitude of local studies, but are criticized with respect to poor generalization capacities. Alternative strategies, such as the use of physically based models of leaf or canopy reflectance, or hybrid approaches, have the potential advantage to be more widely applicable. This paper attempts to assess achievements and shortcomings of these strategies and finds that the often-cited disadvantages of using empirical approaches are becoming less pronounced in the light of recent research results. While retrievals based on physically based models on leaf/needle level are close to laboratory quality, results on canopy level available to date still have considerable deficits. Owing to improved instrumental designs, better data calibration, new approaches for compensating canopy effects, and the use of increasingly efficient methods for establishing data-driven models, the scope of empirical approaches has considerably widened and they have been successfully applied to large areas. The future availability of regularly acquired hyperspectral imagery from Earth orbits will substantially contribute to their generalizability.
关键词： Forest ecosystems,Biochemical traits,Retrieval strategies,Imaging spectroscopy
更新于2025-09-19 17:15:36
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Investigation of Biochemical Alterations in Ischemic Stroke Using Fourier Transform Infrared Imaging Spectroscopy—A Preliminary Study
摘要： Objective: Brain damage, long-term disability and death are the dreadful consequences of ischemic stroke. It causes imbalance in the biochemical constituents that distorts the brain dynamics. Understanding the sub-cellular alterations associated with the stroke will contribute to deeper molecular understanding of brain plasticity and recovery. Current routine approaches examining lipid and protein biochemical changes post stoke can be difficult. Fourier Transform Infrared (FTIR) imaging spectroscopy can play a vital role in detecting these molecular alterations on a sub-cellular level due to its high spatial resolution, accuracy and sensitivity. This study investigates the biochemical and molecular changes in peri-infract zone (PIZ) (contiguous area not completely damaged by stroke) and ipsi-lesional white matter (WM) (right below the stroke and PIZ regions) nine weeks post photothrombotic ischemic stroke in rats. Materials and Methods: FTIR imaging spectroscopy and transmission electron microscopy (TEM) techniques were applied to investigate brain tissue samples while hematoxylin and eosin (H&E) stained images of adjacent sections were prepared for comparison and examination the morphological changes post stroke. Results: TEM results revealed shearing of myelin sheaths and loss of cell membrane, structure and integrity after ischemic stroke. FTIR results showed that ipsi-lesional PIZ and WM experienced reduction in total protein and total lipid content compared to contra-lesional hemisphere. The lipid/protein ratio reduced in PIZ and adjacent WM indicated lipid peroxidation, which results in lipid chain fragmentation and an increase in olefinic content. Protein structural change is observed in PIZ due to the shift from random coil and α-helical structures to β-sheet conformation. Conclusion: FTIR imaging bio-spectroscopy provide novel biochemical information at sub-cellular levels that be difficult to be obtained by routine approaches. The results suggest that successful therapeutic strategy that is based on administration of anti-oxidant therapy, which could reduce and prevent neurotoxicity by scavenging the lipid peroxidation products. This approach will mitigate tissue damage in chronic ischemic period. FTIR imaging bio-spectroscopy can be used as a powerful tool and offer new approach in stroke and neurodegenerative diseases research.
关键词： photothrombotic stroke,Fourier transform infrared (FTIR) imaging spectroscopy,transmission electron microscope (TEM),brain ischemia
更新于2025-09-11 14:15:04
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Properties of the dust in the coma of 67P/Churyumov-Gerasimenko observed with VIRTIS- M
摘要： An investigation is presented of the dust scattering in the coma of 67P/Churyumov–Gerasimenko for the dates of 2015 February 28, March 15 and April 27. A comparison of the morphology of dust continuum maps at 1.1 μm and gas emission shows that for the above dates the spatial distribution of the dust is strongly correlated with H2O but not with CO2 emission. For April 27, the radial pro?le on the illuminated side of the nucleus in the inner coma agrees well with the direct simulation Monte Carlo (DSMC) calculations as the dust is accelerating and ?ows outwards but follows a 1/ρ distribution at distances larger than 4 km from the nucleus. The azimuthal distribution of the dust is narrower than the broader emission of the gas. Afρ values are 1.13 m for 2015 February 28, 2.02 m for April 27, while local values for March 15 are 2.3–5.3 m, depending on the nucleus illumination. In the inner coma, the spectral re?ectivity from 0.35 to 3.5 μm displays a red slope with a change at around 1 μm. From 0.35 to 0.8 μm, the values range from 9 to 12 ± 1 per cent per 100 nm both on the sunlit side and on the dark side. From 1 to 2.5 μm, the values are 1.7 ± 0.2 per cent per 100 nm on the sunlit side and 3 ± 1 per cent per 100 nm on the dark side. For the August 26 jet, no signi?cant increase of the colour gradient with distance from the nucleus could be observed, nor any signi?cant difference detected between the jet and the background coma.
关键词： methods: data analysis – methods: observational – techniques: imaging spectroscopy – comets: individual: 67P/Churyumov–Gerasimenko.
更新于2025-09-11 14:15:04
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - UAV Spectroscopy: Current Sensors, Processing Techniques and Theoretical Concepts for Data Interpretation
摘要： In the last ten years, UAV sensing systems have become a frequently used tool for quantitative remote sensing. Many research teams have started to build their own sensing systems based on newly available consumer grade software packages and increasing computing power. Additionally, camera manufacturers are now building costume made sensors for UAV sensing. This talk will give an introduction and overview and comparison on current sensor technologies, processing techniques and theoretical concepts for data interpretation in quantitative spectral remote sensing with UAVs. Additionally, some challenges are outlined and systematic differences to data from non-imaging spectroscopy measurements are explained.
关键词： unmanned aerial vehicles,2D imagers,Imaging spectroscopy
更新于2025-09-10 09:29:36
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Mode identification based on time-series spectrophotometry for the bright rapid sdB pulsator EC 01541?1409
摘要： We present an analysis of time-resolved spectrophotometry gathered with FORS/VLT for the rapidly pulsating hot B subdwarf EC 01541?1409 with the aim of identifying the degree index (cid:2) of the larger amplitude modes. This mode identi?cation can be extremely useful in detailed searches for viable asteroseismic models in parameter space, and can be crucial for testing the validity of a solution a posteriori. To achieve it, we exploit the (cid:2)-dependence of the monochromatic amplitude, phase, and velocity-to-amplitude ratio of a mode as a function of wavelength. We use the (cid:2)-sensitive phase lag between the ?ux perturbation and the radial velocity as an additional diagnostic tool. On this basis, we are able to unambiguously identify the dominant 140.5 s pulsation of our target as a radial mode, and the second-highest amplitude periodicity at 145.8 s as an (cid:2) = 2 mode. We further exploit the exceptionally high-sensitivity data that we gathered for the dominant mode to infer modal properties that are usually quite di?cult to estimate in sdB pulsators, namely the physical values of the dimensionless radius, temperature, and surface gravity perturbations.
关键词： stars: oscillations,stars: individual: EC 01541-1409,techniques: imaging spectroscopy,stars: atmospheres,stars: variables: general,asteroseismology
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - A Simplified 3D Radiative Transfer Approach for the Retrieval of Chemical and Structural Properties of Individual Tree Crowns from Hyperspectral Data
摘要： In this work, we used hyperspectral remote sensing and a simplified three-dimensional radiative transfer approach to retrieve structural and chemical properties of individual tree crowns (ITCs) from a tropical forest area. First, a Look-Up-Table of simulated ITC reflectance was built by randomly varying parameters of the DART and PROSPECT models. Then, simulated and experimental reflectance of ITCs were compared in terms of spectral similarity. Finally, model parameters that yielded simulations spectrally similar to experimental data were related to sub-pixel fractions and narrow-band vegetation indices computed from the hyperspectral images. DART canopy structural parameters were related to the proportion of non-photosynthetic vegetation (NPV) (R2=0.65), green photosynthetic vegetation (GV) (R2=0.72) and shade (R2=0.34) estimated within ITCs. PROSPECT parameters describing foliar chemical traits such as Chlorophyll a+b (Cab) and Carotenoids (Cxc) were related to the ratio of TCARI/OSAVI (R2=0.77) indices and to the simple ratio between reflectance at 515 nm and 570 nm (R515/R570) (R2=0.42), respectively.
关键词： imaging spectroscopy,tropical forest,DART,traits
更新于2025-09-09 09:28:46
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67P/Churyumov-Gerasimenko active areas before perihelion identified by GIADA and VIRTIS data fusion
摘要： We characterised 67P/Churyumov-Gerasimenko?s cometary activity during its inbound arc before perihelion (August 2014-January 2015). We focused on the geomorphological regions of the Northern hemisphere observed by the ESA/Rosetta space probe during this time period. The GIADA dust detector characterised the physical properties of the fluffy and compact particles ejected from the nucleus; the VIRTIS imaging spectrometer detected exposed water ice. We identified specific cometary active areas by adopting the following GIADA and VIRTIS indicators: a) The decrease with increasing temperature of the centre of the 3.2-?m absorption band and of the spectral slope between 1.1 and 1.9??m, as measured by VIRTIS, which are both possible effects of water ice exposition. b) The number of fluffy and compact particles ejected from a specific region, which we determined by tracing dust particles in the coma, as detected by GIADA, back down to the nucleus. The correlation between GIADA and VIRTIS indicators led us to conclude that dust emission causes exposition of water ice on the surface of the nucleus, and fluffy and compact particles have common ejection regions; their lack of correlation in the coma is due to spread induced by their different velocities. We find that the most active regions are located in the neck (Hapi and Seth) and in the body (Ash, Babi and Aten) of the comet. These regions are also the ones most illuminated during the considered observation period, indicating that insolation is the main, if not only, driver of cometary activity.
关键词： Methods: data analysis,Instrumentation: detectors,Comets: Churyumov-Gerasimenko,Techniques: imaging spectroscopy
更新于2025-09-09 09:28:46