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Spectral analysis is successfully adopted in several fields. However, the requirements and the constraints of the different cases may be so varied that not only the tuning of the analysis parameters but also the choice of the most suitable technique can be a difficult task. For this reason, it is important that a designer of a measurement system for spectral analysis has knowledge about the behaviour of the different techniques with respect to the operating conditions. The case that will be considered is the realization of a numerical instrument for the real-time measurement of the spectral characteristics of a multi-tone signal (amplitude, frequency, and phase). For this purpose, different signal processing techniques can be used, that can be classified as parametric or non-parametric methods. The first class includes those methods that exploit the a priori knowledge about signal parameters, such as the spectral shape of the signal to be processed. Thus, a self-configuring procedure based on a parametric algorithm should include a preliminary evaluation of the number of components. The choice of the right method among several proposals in the literature is fundamental for any designer and, in particular, for the developers of spectral analysis software, for real-time applications and embedded devices where time and reliability constrains are arduous to fulfil. Different aspects should be considered: the desired level of accuracy, the available elaboration resources (memory depth and processing speed), and the signal parameters. The present paper details a comparison of some of the most effective methods available in the literature for the spectral analysis of signals (IFFT-2p, IFFT-3p, and IFFTc, all based on the use of an FFT algorithm, while improving the spectral resolution of the DFT with interpolation techniques and three parametric algorithms—MUSIC, ESPRIT, and IWPA). The methods considered for the comparison will be briefly described, and references to literature will be given for each one of them. Then, their behaviour will be analysed in terms of systematic contribution and uncertainty on the evaluated frequencies of the spectral tones of signals created from superimposed sinusoids and white Gaussian noise.

Hypersharpening consists in generating an unobservable high-spatial-resolution hyperspectral image by fusing an observed low-spatial-resolution hyperspectral image with an observed high-spatial-resolution panchromatic or multispectral one. The obtained image preserves the high spectral resolution of the first image and the high spatial resolution of the second one. Unlike standard hypersharpening methods that do not consider the spectral variability phenomenon, in this letter, a new approach, which addresses this phenomenon, is proposed for fusing hyperspectral and multispectral remote sensing images. This approach, linked to linear spectral unmixing methods, is based on an extension of nonnegative matrix factorization (NMF), namely the inertia-constrained pixel-by-pixel NMF (IP-NMF) algorithm. The developed fusion algorithm, called hyperspectral and multispectral data fusion based on IP-NMF (HMF-IPNMF), is applied to synthetic and real data sets. Experimental results clearly show that the developed fusion method yields sharpened hyperspectral images with higher spectral and spatial fidelities when compared to those provided by tested state-of-the-art methods that do not take spectral variability into account.

G21.5 - 0.9 is a young plerionic composite supernova remnant (SNR) hosting a bright pulsar wind nebula. The previous X-ray studies reported that the X-ray spectrum of the entire SNR can be fitted with a non-thermal spectral model, while the recent Chandra studies have pointed out that its X-ray spectrum also shows weak thermal emission. With this motivation, we search for a feature of the thermal emission from the SNR using the high spectral resolution of Suzaku X-ray Imaging Spectrometer data observed in 2007 and 2009. We found that both a pure non-thermal model and a non-thermal plus thermal model yield statistically acceptable fits. The two-component X-ray spectrum gives a photon index of ∼ 1.92 and an electron temperature of ∼ 0.2 keV, and an ionization time-scale of more than 4 × 10 12 cm-3 s. We also performed XRISM and Athena simulations of the same region on the SNR to investigate any sign of thermal emission. Our simulations show the potential of the future missions Athena and XRISM for revealing the thermal emission from G21.5 - 0.9, where the elemental lines of Ne, Mg, and Si can be well traced.

Cyanobacterial harmful algal blooms are an increasing threat to coastal and inland waters. These blooms can be detected using optical radiometers due to the presence of phycocyanin (PC) pigments. The spectral resolution of best-available multispectral sensors limits their ability to diagnostically detect PC in the presence of other photosynthetic pigments. To assess the role of spectral resolution in the determination of PC, a large (N = 905) database of colocated in situ radiometric spectra and PC are employed. We first examine the performance of selected widely used machine-learning (ML) models against that of benchmark algorithms for hyperspectral remote sensing reflectance ( $R_{{rs}})$ spectra resampled to the spectral configuration of the Hyperspectral Imager for the Coastal Ocean (HICO) with a full-width at half-maximum (FWHM) of < 6 nm. Results show that the multilayer perceptron (MLP) neural network applied to HICO spectral configurations (median errors < 65%) outperforms other ML models. This model is subsequently applied to $R_{{rs}}$ spectra resampled to the band configuration of existing satellite instruments and of the one proposed for the next Landsat sensor. These results confirm that employing MLP models to estimate PC from hyperspectral data delivers tangible improvements compared with retrievals from multispectral data and benchmark algorithms (with median errors between ~73% and 126%) and shows promise for developing a globally applicable cyanobacteria measurement approach.

Aerosol extinction coefficient (AEC) is a crucial factor of aerosol optical properties that have an important influence on the atmospheric process. As a combination of laser technology and radar technology, LiDAR is a powerful remote sensing technology for aerosol measurement. However, many uncertainties still exist in LiDAR data retrieval because frequently used retrieval methods need some assumptions or complex numerical operations for retrieving AEC, which may cause large deviation. In this letter, combining the advantages and disadvantages of Mie scattering LiDAR and high spectral resolution LiDAR (HSRL), a new inversion model based on deep belief network (DBN) is proposed to predict AEC, which can effectively avoid the uncertainty caused by many assumptions and improve the detection accuracy of Mie scattering LiDAR. The experiment results indicate that the trained DBN model is robust and satisfactory and provides a competitive solution for predicting AEC of Mie scattering LiDAR. In addition, this letter reveals that deep learning method has huge potential for LiDAR data retrieval.

Owing to easy acquisition and large coverage from the space, multispectral (MS) imaging has garnered growing interest in various applications of remote sensing. However, the limited spectral information of MS data, to a great extent, leads to difficulties in classifying the materials more accurately, particularly for those classes that have very similar visual appearances. To address this issue effectively, we attempt to enhance the spectral resolution of MS imagery, enabling the identification of materials at a more precise level by the means of richer spectral information. More specifically, we propose to learn locality-constrained sparse coding (LCSC) for short, on partially overlapped hyperspectral (HS)-MS pairs (i.e., dictionary). LCSC is capable of capturing neighboring relations well by enforcing the local constraint for each pixel. Such a strategy makes it possible to better reconstruct HS products from MS images and partially overlapped HS images. Reconstruction and unmixing are explored as potential applications to assess the performance of spectral enhancement. Extensive experiments are conducted on two HS-MS data sets in comparison with several state-of-the-art baselines, which demonstrate the effectiveness of the proposed LCSC algorithm in the task of spectral enhancement.

The advanced hyperspectral imager (AHSI) is one of the sensors aboard the Chinese Gaofen-5 (GF-5) satellite, possessing characteristics of high spatial and spectral resolution, as well as width swath. To better understand the radiometric performance of GF-5/AHIS after its launch, this article presents an on-orbit radiometric calibration approach for AHSI visible and near-infrared (VNIR) and shortwave infrared (SWIR) sensors from field automatic observations with a field spectrometer in the absence of SWIR measurements. A spectrum extension method was proposed to extend the retrieved surface hyperspectral reflectance in the VNIR spectral ranges to SWIR by incorporating the historical hyperspectral reflectance library. The radiometric calibration coefficients of GF-5/AHSI were calculated by linear fitting of the observed digital number (DN) values with GF-5/AHSI and predicted at-sensor radiances with MODTRAN 5 based on extended hyperspectral surface reflectance. Comparisons with onboard calibration results were also performed, and the averaged relative differences were within 5% with 1δ standard deviations less than 10% for most bands, except for those in the atmospheric absorption and low signal-to-noise ratio bands. The comparison results indicate that the on-site radiometric calibration results are consistent with the onboard results, and the operational on-orbit radiometric calibration approach is reliable in the case that there are no measurements in the SWIR spectra range. The on-orbit radiometric performance of GF-5/AHSI rapidly degraded during the first several months after its launch and then tended to be relatively stable.

Miniaturized spectrometers are being developed in the recent few years leveraging the rapidly-progressing technology and triggering new markets in the field of on-site and mobile spectroscopic analysis. Although some devices were commercialized for the near-infrared spectroscopy (NIRS), their size and cost still don't meet the requirements for the ubiquitous deployment of the spectrometer as a spectral sensor needed for the smart industry and IoT applications. In this work we report an integrated microelectromechanical system (MEMS)-based Fourier Transform Infrared (FT-IR) spectral sensor. A monolithic scanning Michelson interferometer MEMS chip and an extended InGaAs photodetector chip are integrated with a micro-optical system in a tiny package with a footprint of 18 mm, presenting the smallest reported FT-IR solution to date. A compact light source head is designed and implemented targeting diffuse-reflection applications. The reported sensor's spectral resolution is about 66.6 cm-1 across the spectral range of 1350-2550 nm. The signal-to-noise ratio (SNR) achieved is 8000:1 at 2400 nm in 2 seconds, with an order of magnitude improvement with respect to previously reported fiber-coupled solution. The presented solution provides a low cost, low power, wide wavelength range NIR spectral sensor that can be manufactured with high volumes leveraging economies of scale.

We present observations and models of the kinematics and distribution of neutral hydrogen (HI) in the superthin galaxy FGC 1440 with an optical axial ratio $a/b = 20.4$. Using the Giant Meterwave Radio telescope (GMRT), we imaged the galaxy with a spectral resolution of 1.7 $\rm kms^{-1}$ and a spatial resolution of $15" \times 13.5"$. We find that FGC 1440 has an asymptotic rotational velocity of 141.8 $\rm kms^{-1}$ . The structure of the HI disc in FGC 1440 is that of a typical thin disc warped along the line of sight, but we can not rule out the presence of a central thick HI disc. We find that the dark matter halo in FGC 1440 could be modeled by a pseudo-isothermal (PIS) profile with $\rm R_{c}/ R_{d}, Comment: Accepted for publication in MNRAS

Vibrational sum-frequency generation (VSFG) spectroscopy, a surface-specific technique, was shown to be useful even for characterizing the vibrational optical activity of chiral molecules in isotropic bulk liquids. However, accurately determining the spectroscopic parameters is still challenging because of the spectral congestion of chiroptical VSFG peaks with different amplitudes and phases. Here, we show that a time-variable infrared-visible chiroptical three-wave-mixing technique can be used to determine the spectroscopic parameters of second-order vibrational response signals from chiral chemical liquids. For varying the delay time between infrared and temporally asymmetric visible laser pulses, we measure the chiral VSFG, achiral VSFG, and their interference spectra of bulk R-(+)-limonene liquid and perform a global fitting analysis for those time-variable spectra to determine their spectroscopic parameters accurately. We anticipate that this time-variable VSFG approach will be useful for developing nearly background-free chiroptical characterization techniques with enhanced spectral resolution.

Hyperspectral images (HSIs) are the images that have a high spectral resolution with hundreds of bands. HSIs are widely used in the precise identification and classification of the materials and surfaces. However, they have a low spatial resolution caused by the limited capacity of the sensors responsible for capturing the images. In view of this, the preprocessing techniques are used to increase the spatial resolution of the HSIs and enable greater precision in the subsequent processing stages. This letter presents the development of a hardware accelerator specially designed to process a pansharpening algorithm that fuses the hyperspectral and panchromatic images to produce a high spatial resolution HSI. The experimental results demonstrate that the processor is energy-efficient and can be used for onboard processing in a small spacecraft, such as the satellites.

Sentinel-3 is a newly launched satellite implemented by the European Space Agency (ESA) for global observation. The Ocean and Land Colour Imager (OLCI) sensor onboard Sentinel-3 provides 21 band images with a fine spectral resolution and is of great value for ocean, land and atmospheric monitoring. The two platforms (Sentinel-3A and -3B) can provide OLCI images at an almost daily temporal resolution. The coarse spatial resolution of the 21 band OLCI images (i.e., 300 m), however, limits greatly their utility for local, precise monitoring. Sentinel-2, another satellite provided by ESA, carries the Multispectral Imager (MSI) sensor which can supply much finer spatial resolution (e.g., 10 m and 20 m) images. This paper introduces a new fusion framework integrating spatio-temporal-spectral information for downscaling Sentinel-3 OLCI images, which has two parts. Based on bands with similar wavelengths (i.e., bands 2, 3, 4 and 8a for Sentinel-2 and bands Oa4, Oa6, Oa8 and Oa17 for Sentinel-3), the four Sentinel-3 bands are first downscaled to the spatial resolution of Sentinel-2 images by applying spatio-temporal fusion to Sentinel-2 MSI and Sentinel-3 OLCI images. Then, to take full advantage of all 21 available OLCI bands of the Sentinel-3 images, the extended image pair-based spatio-spectral fusion (EIPSSF) method is proposed in this paper to downscale the other 17 bands. EIPSSF is performed based on the new concept of the extended image pair (EIP) and by exploiting existing spatio-temporal fusion approaches. The framework consisting of spatio-temporal and spatio-spectral fusion is entirely general, which provides a practical solution for comprehensive downscaling of Sentinel-3 OLCI images for fine spatial, temporal and spectral resolution monitoring.

Characteristic features of magnetoplasmonic responses in higher-order multipolar (quadrupolar and octupolar) modes of Ag nanoparticles (from 90 to 200 nm in diameter) are demonstrated for the first time using magnetic circular dichroism (MCD) spectroscopy. In optical extinction spectra, with an increase in the size of the nanoparticles, the red shift of dipolar plasmon peaks and the appearance of higher-order multipolar resonances can reasonably be observed. Aside from the dipolar and quadrupolar modes, the octupolar plasmonic extinction is very weak and almost unresolved. In contrast, strikingly, MCD shows a very sharp and intense peak (or valley) for the octupolar resonance, meaning its unique properties with high sensitivity and enhanced spectral resolution. MCD responses assignable to the quadrupolar mode have a distinct derivative-like shape, which is different from those observed for Ag nanocubes and nanodecahedra in our previous studies. We then discuss this behavior from the viewpoint of size and/or polyhedral shape inhomogeneity.

Introduction: Talker-specific adaptation facilitates speech recognition in normal-hearing listeners. This study examined talker adaptation in adult cochlear implant (CI) users. Three hypotheses were tested: (1) high-performing adult CI users show improved word recognition following exposure to a talker (“talker adaptation”), particularly for lexically hard words, (2) individual performance is determined by auditory sensitivity and neurocognitive skills, and (3) individual performance relates to real-world functioning. Methods: Fifteen high-performing, post-lingually deaf adult CI users completed a word recognition task consisting of 6 single-talker blocks (3 female/3 male native English speakers); words were lexically “easy” and “hard.” Recognition accuracy was assessed “early” and “late” (first vs. last 10 trials); adaptation was assessed as the difference between late and early accuracy. Participants also completed measures of spectral-temporal processing and neurocognitive skills, as well as real-world measures of multiple-talker sentence recognition and quality of life (QoL). Results: CI users showed limited talker adaptation overall, but performance improved for lexically hard words. Stronger spectral-temporal processing and neurocognitive skills were weakly to moderately associated with more accurate word recognition and greater talker adaptation for hard words. Finally, word recognition accuracy for hard words was moderately related to multiple-talker sentence recognition and QoL. Conclusion: Findings demonstrate a limited talker adaptation benefit for recognition of hard words in adult CI users. Both auditory sensitivity and neurocognitive skills contribute to performance, suggesting additional benefit from adaptation for individuals with stronger skills. Finally, processing differences related to talker adaptation and lexical difficulty may be relevant to real-world functioning.

According to spectrophotometric measurements of Jupiter and Saturn obtained in 2014–2017 on an echelle spectrometer equipped with a CCD receiver at the Cassegrain focus of the 2-m telescope of the Nasreddin Tusi Shamakhy Astrophysical Observatory of the Azerbaijan National Academy of Sciences (ShAO), weak quadrupole lines of molecular hydrogen of the H2 (4-0) band in the visible spectral region with a spectral resolution of R = 14 000 and R = 56 000 were studied. Using the lines of the H2 (4-0) S(0) and S(1) bands, the pressure values at the levels of their formation, the rotational temperature, the content of molecular hydrogen in the above-cloud atmosphere, the amount of absorbing gas per the average free path of photons between two scattering acts in the cloud layer, and the specific gas content per unit free path in different parts of the disk of Jupiter and Saturn were calculated. It was necessary to monitor the change in the S4(2)/S4(0) ratio along the disk of Jupiter and Saturn in the spatial and temporal intervals. According to our measurements in 2016, the ratio W(0)/W(2) = 3.5 ± 0.6 for Jupiter, and W(0)/W(2) > 2.5 ± 0.4 for Saturn was obtained; in general, the Great Red Spot (GRS) has an average temperature of approximately 124 ± 6K.

Future X-ray astrophysics experiments require multiplexed readout of high fill-factor, kilo-pixel arrays of transition-edge sensors (TESs), with very high spectral resolution over a broad range of energies. In this paper we report on a prototype kilo-pixel array of Mo/Au TESs readout with 8-column by 32-row time-division multiplexing (TDM). This system is being used to demonstrate the critical detector and readout technology for ESA's Athena X-IFU, and when complete will be used in laboratory astrophysics experiments. Our array and TDM readout have demonstrated a combined full-width-at-half-maximum energy resolution, including > 200 pixels, of: 1.95 eV for Ti-Kα (4.5 keV), 1.97 eV for Mn-Kα (5.9 keV), 2.16 eV for Co-Kα (6.9 keV), 2.33 eV for Cu-Kα (8 keV), 3.26 eV for Br-Kα (11.9 keV). The 1 sigma statistical errors are ≤0.01 eV for all spectra. These results meet the broad-band resolution requirements for X-IFU with margin.

We show that a Leray–Hopf weak solution to the three-dimensional Navier–Stokes the initial value problem is regular in (0, T] if $$\Vert \nabla u_0^+\Vert _2$$ (or $$\Vert \nabla u_0^-\Vert _2$$ ) for initial value $$u_0$$ and $$\max \{\frac{d{\mathcal H}}{dt},0\}$$ (or $$\max \{-\frac{d{\mathcal H}}{dt},0\}$$ ) are suitably small depending on the initial kinetic energy and viscosity, where $$u_0^+=\int _0^{\infty } dE_\lambda u_0$$ , $$u_0^-=\int _{-\infty }^0 dE_\lambda u_0$$ , $$\{E_\lambda \}_{\lambda \in {\mathbb R}}$$ is the spectral resolution of the $$\mathrm{curl}$$ operator and $${\mathcal H}\equiv \int _{\mathbb R^3}u\cdot \mathrm{curl} u\,dx$$ is the helicity of the fluid flow. The results suggest that the helicity change rate rather than the magnitude of the helicity itself affects regularity of the viscous incompressible flows. More precisely, an initially regular viscous incompressible flow with suitably small positive or negative maximal helical component does not lose its regularity as long as the total helical behavior of the flow with respect to time is not decreasing, or even weakened at a moderate rate in accordance with the initial kinetic energy and viscosity.

Due to emerging high spectral resolution, remote sensing techniques and ongoing developments to retrieve the spectrally resolved vegetation fluorescence spectrum from several scales, the light reactions of photosynthesis are receiving a boost of attention for the monitoring of the Earth's carbon balance. Sensor-retrieved vegetation fluorescence (from leaf, tower, airborne or satellite scale) originating from the excited antenna chlorophyll a molecule has become a new quantitative biophysical vegetation parameter retrievable from space using global imaging techniques. However, to retrieve the actual quantum efficiencies, and hence a true photosynthetic status of the observed vegetation, all signal distortions must be accounted for, and a high-precision true vegetation reflectance must be resolved. ESA's upcoming Fluorescence Explorer aims to deliver such novel products thanks to technological and instrumental advances, and by sophisticated approaches that will enable a deeper understanding of the mechanics of energy transfer underlying the photosynthetic process in plant canopies and ecosystems.

High resolution spectra of quasar absorption systems provide the best constraints on temporal or spatial changes of fundamental constants in the early universe. An important systematic that has never before been quantified concerns model non-uniqueness. The absorption structure is generally complicated, comprising many blended lines. This characteristic means any given system can be fitted equally well by many slightly different models, each having a different value of \alpha, the fine structure constant. We use AI Monte Carlo modelling to quantify non-uniqueness. Extensive supercomputer calculations are reported, revealing new systematic effects that guide future analyses: (i) Whilst higher signal to noise and improved spectral resolution produces a smaller statistical uncertainty for \alpha, model non-uniqueness adds a significant additional uncertainty. (ii) Non-uniqueness depends on the line broadening mechanism used. We show that modelling the spectral data using turbulent line broadening results in far greater non-uniqueness, hence this should no longer be done. Instead, for varying \alpha studies, it is important to use the more physically appropriate compound broadening. (iii) We have studied two absorption systems in detail. Generalising thus requires caution. Nevertheless, if non-uniqueness is present in all or most quasar absorption systems, it seems unavoidable that attempts to determine the existence (or non-existence) of spacetime variations of fundamental constants is best approached using a statistical sample., Comment: 17 pages, 11 figures

Purpose Reliable detection and fitting of macromolecules (MM) are crucial for accurate quantification of brain short-echo time (TE) 1 H-MR spectra. An experimentally acquired single MM spectrum is commonly used. Higher spectral resolution at ultra-high field (UHF) led to increased interest in using a parametrized MM spectrum together with flexible spline baselines to address unpredicted spectroscopic components. Herein, we aimed to: (1) implement an advanced methodological approach for post-processing, fitting, and parametrization of 9.4T rat brain MM spectra; (2) assess the concomitant impact of the LCModel baseline and MM model (ie, single vs parametrized); and (3) estimate the apparent T2 relaxation times for seven MM components. Methods A single inversion recovery sequence combined with advanced AMARES prior knowledge was used to eliminate the metabolite residuals, fit, and parametrize 10 MM components directly from 9.4T rat brain in vivo 1 H-MR spectra at different TEs. Monte Carlo simulations were also used to assess the concomitant influence of parametrized MM and DKNTMN parameter in LCModel. Results A very stiff baseline (DKNTMN ≥ 1 ppm) in combination with a single MM spectrum led to deviations in metabolite concentrations. For some metabolites the parametrized MM showed deviations from the ground truth for all DKNTMN values. Adding prior knowledge on parametrized MM improved MM and metabolite quantification. The apparent T2 ranged between 12 and 24 ms for seven MM peaks. Conclusion Moderate flexibility in the spline baseline was required for reliable quantification of real/experimental spectra based on in vivo and Monte Carlo data. Prior knowledge on parametrized MM improved MM and metabolite quantification.

Existing structured illumination microscopy (SIM) allows super-resolution live-cell imaging in few color channels that provide merely morphological information but cannot acquire the sample spectrum that is strongly relevant to the underlying physicochemical property. We develop hyperspectral SIM which enables high-speed spectral super-resolution imaging in SIM for the first time. Through optically mapping the three-dimensional (x, y, and λ) datacube of the sample to the detector plane, hyperspectral SIM allows snapshot spectral imaging of the SIM raw image, detecting the sample spectrum while retaining the high-speed and super-resolution characteristics of SIM. We demonstrate hyperspectral SIM imaging and reconstruct a datacube containing 31 super-resolution images of different wavelengths from only 9 exposures, achieving a 15 nm spectral resolution. We show time-lapse hyperspectral SIM imaging that achieves an imaging speed of 2.7 s per datacube-31-fold faster than the existing wavelength scanning strategy. To demonstrate the great prospects for further combining hyperspectral SIM with various spectral analysis methods, we also perform spectral unmixing of the hyperspectral SIM result while imaging the spectrally overlapped sample.

We present the HR-pyPopStar model, which provides a complete set (in ages) of high resolution (HR) Spectral Energy Distributions of Single Stellar Populations. The model uses the most recent high wavelength-resolution theoretical atmosphere libraries for main sequence, post-AGB/planetary nebulae and Wolf-Rayet stars. The Spectral Energy Distributions are given for more than a hundred ages ranging from 0.1 Myr to 13.8 Gyr, at four different values of the metallicity (Z = 0.004, 0.008, 0.019 and 0.05), considering four different IMFs. The wavelength range goes from 91 to 24 000 {\AA} in linear steps {\delta}{\lambda} = 0.1 {\AA}, giving a theoretical resolving power R_{th,5000} ~ 50 000 at 5000 {\AA}. This is the main novelty of these spectra, unique for their age and wavelength ranges. The models include the ionising stellar populations that are relevant both at young (massive hot stars) as well as old (planetary nebulae) ages. We have tested the results with some examples of HR spectra recently observed with MEGARA at GTC. We highlight the importance of wavelength-resolution in reproducing and interpreting the observational data from the last and forthcoming generations of astronomical instruments operating at 8-10m class telescopes, with higher spectral resolution than their predecessors., Comment: 24 pages, 17 figures

Intensity mapping of multiple emission lines is emerging as a new branch to astronomy, to probe both properties of ionizing sources and the medium between, in particular the intergalactic medium. For Epoch of Reionization (EoR) studies, both multi-line experiments and analysis methods are still in their infancy. Here we explore optimal survey parameters for Ly$\alpha$ (and H$\alpha$) intensity mapping up to high redshifts of reionization, and requirements for optimised synergy with 21cm experiments. We investigate line sensitivity, spectral resolution and detector pixel size requirements for optimal (high signal-to-noise) mission output. Power and cross-power spectra in a fiducial setup are derived, as are mock intensity maps. For line power spectrum measurements a cumulative signal-to-noise of O$\left(10^3 \right)$, and for respective cross-spectra with SKA 21cm observations of O$\left(10\right)$ to O$\left(10^2\right)$ are possible per redshift bin around the midpoint of reionization. These high signal-to-noise tomographic measurements are in reach for line sensitivities $>8\times 10^{-18}$erg$\,$s$^{-1}$sr$^{-1}$Hz$^{-1}$, spectral resolution $R>250$ and detector pixel sizes $, Comment: 12 pages, 6 (+2) figures. Figure 4 and 6 as well as section 6 present main conclusions. v2 adds prospects for measurements with HERA, as well appendices with background on IGM attenuation, auto-power spectra, and the Knox criterion for optimised errors

The observational data of an H2О maser at a frequency of 22.2280 GHz in the dark reflection nebula NGC 2071 in the direction of the infrared object IRS 1 at the target coordinates RA(2000) = $${{05}^{{\text{h}}}}{{47}^{{\text{m}}}}04_{.}^{{\text{s}}}758$$ , DEC(2000) = $$00{}^\circ 21' 42_{.}^{'' }700$$ have been processed as part of the scientific program of the ground-space interferometer RadioAstron. The duration of the session on January 11, 2014 was 70 min. The space radio telescope (SRT-10) and three radio telescopes of the ground-based network took part in the observations: RT-32 (Medicina, Italy), RT-32 (Torun, Poland), and RT-64 (Kalyazin, Russia). The following parameters were implemented: angular resolution 70 μs at the ground-space baseline with maximum baseline projections 3.1 ED ( $$ \sim {\kern 1pt} 40{\kern 1pt} {\kern 1pt} 000$$ km); synthesized beam of the ground-based part of the interferometer $$0.006'' \times 0.0006'' $$ (PA = –23°); spectral resolution 7.81 kHz (i.e., 0.11 km/s). A map of the distribution of maser spots with 13 spatial components was obtained. The map has a size $$ \sim {\kern 1pt} 100 \times 100$$ mas (milliarcseconds), which corresponds to $$ \sim 40 \times 40$$ AU at a distance of 390 pc to the nebula. The range of the line-of-sight velocities of the components is 4.7–20.5 km/s with a width of spectral features 0.2–0.6 km/s; the density of the correlated flux at the line maximum varies from $$ \sim {\kern 1pt} 4$$ to $$ \sim {\kern 1pt} 29$$ Jy. There was recorded one spatial component (with a radial velocity of 14.3 km/s) for which there was a correlation at the ground-space baselines SRT–Tr and SRT–Mc at an ultrahigh angular resolution with a reliability level above 6σ. Based on the analysis of the dependence of the visibility function on the baseline projections, a two-component model is proposed for the spatial structure of this component with the angular dimensions of the extended and compact constituents 4 mas and 0.06 mas, i.e., 1.56 AU (with an uncertainty of 10%) and 0.023 AU (with an uncertainty of 50%), respectively.

The scanning Fabry-Perot interferometer (FPI) - is the oldest method of optical 3D spectroscopy. It is still in use because of the high spectral resolution it provides over a large field of view. The history of the application of this method for the study of extended ob jects (nebulae and galaxies) and the technique of data reduction and analysis are discussed. The paper focuses on the performing observations with the scanning FPI on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). The instrument is currently used as a part of the SCORPIO-2 multimode focal reducer. The results of studies of various galactic and extragalactic objects with the scanning FPI on the 6-m telescope - star-forming regions and young stellar objects, spiral, ring, dwarf and interacting galaxies, ionization cones of active galactic nuclei, galactic winds, etc. are briefly discussed. Further prospects for research with the scanning FPI of the SAO RAS are discussed., Comment: 25 pages, 8 figures, accepted to Astrophysical Bulletin

The absorption spectra of a water molecule perturbed by argon pressure were measured in the 6700–7650 cm−1 region. The spectra were recorded at an IFS 125HR Fourier spectrometer with a high signal-to-noise ratio at a room temperature with a spectral resolution of 0.01 cm−1. The argon pressure was varied from 0 to 0.9 atm. Using three line profile models (the traditional Voigt profile; the quadratic Voigt profile, which depends on the speed of an absorbing molecule; and the Hartmann–Tran profile), the parameters of the absorption lines of the water molecule were calculated. A better agreement with the experimental data is provided by the Hartmann–Tran profile. It is suggested to use a relatively simple Voigt profile for mass measurements at pressures above 300 mbar.

Solar-induced chlorophyll fluorescence (SIF) emissions were estimated by the "area-ratio Fraunhofer line depth (aFLD) method", a new retrieval methodology in spectra from a low spectral resolution (SR) spectroradiometer (MS-700: full width half maximum (FWHM) of 10 nm and spectral sampling interval of 3.3 nm), assisted with a scaling to reference SIF detected from high SR spectrum. The sparse pixels of a spectrum of low SR misses detecting the minimum of the O2A absorption band around at 760 nm, which makes the SIF detection by conventional FLD methods lose accuracy considerably. To overcome this, the aFLD method uses the definite integral of spectra over a wide interval between 750 and 780 nm. The integration of the spectrum is insusceptible to the change in shape of the depression curve, leading to higher accuracy of the aFLD method. Daily SIF, calculated by the aFLD method using the spectra obtained with MS-700, was scaled to reference daily SIF calculated by the spectral fitting method using the spectra obtained from August to December 2019 with an ultrafine SR spectroradiometer (QE Pro, FWHM = 0.24 nm). As a result, SIF calculated from MS-700 spectra by aFLD method was strongly correlated with the reference SIF from QE Pro spectra (r2 = 0.81) and was successfully scaled. Then, the scaled 11-year SIF from MS-700 at a deciduous broadleaf forest showed the correlation with GPP at multiple time steps: daily, monthly, and yearly, consistently during 2008–2018. The comparison of aFLD-derived SIF with the global Orbiting Carbon Observatory-2 (OCO-2) SIF data set (GOSIF) showed high correlation on monthly values during 2008–2017 (r2 = 0.85). The combining approach of the aFLD method with a scaling to reference SIF successfully detected long-term canopy SIF emissions, which has great potential to provide essential information on ecosystem-level photosynthesis.

Fluorine-containing compounds comprise 20 to 30 percent of all commercial drugs, and the proportion of fluorinated pharmaceuticals is rapidly growing. While magic angle spinning (MAS) NMR spectroscopy is a popular technique for analysis of solid pharmaceutical compounds, fluorine has been underutilized as a structural probe so far. Here, we report a fast (40-60 kHz) MAS 19F NMR approach for structural characterization of fluorine-containing crystalline pharmaceutical compounds at natural abundance, using the antimalarial fluorine-containing drug mefloquine as an example. We demonstrate the utility of 2D 19F-13C and 19F-19F dipolar-coupling-based correlation experiments for 19F and 13C resonance frequency assignment, which permit identification of crystallographically inequivalent sites. The efficiency of 19F-13C cross-polarization and the effect of 1H and 19F decoupling on spectral resolution and sensitivity were evaluated in a broad range of experimental conditions. We further demonstrate a protocol for measuring accurate interfluorine distances based on 1D DANTE-RFDR experiments combined with multispin numerical simulations.

High spectral resolution (or hyperspectral) infrared (IR) sounders onboard low earth orbiting satellites provide high vertical resolution atmospheric information for numerical weather prediction (NWP) models. In contrast, imagers on geostationary (GEO) satellites provide high temporal and spatial resolution which are important for monitoring the moisture associated with severe weather systems, such as rapidly developing local severe storms (LSS). A hyperspectral IR sounder onboard a geostationary satellite would provide four-dimensional atmospheric temperature, moisture, and wind profiles that have both high vertical resolution and high temporal/spatial resolutions. In this work, the added-value from a GEO-hyperspectral IR sounder is studied and discussed using a hybrid Observing System Simulation Experiment (OSSE) method. A hybrid OSSE is distinctively different from the traditional OSSE in that, (a) only future sensors are simulated from the nature run and (b) the forecasts can be evaluated using real observations. This avoids simulating the complicated observation characteristics of the current systems (but not the new proposed system) and allows the impact to be assessed against real observations. The Cross-track Infrared Sounder (CrIS) full spectral resolution (FSR) is assumed to be onboard a GEO for the impact studies, and the GEO CrIS radiances are simulated from the ECMWF Reanalysis v5 (ERA5) with the hyperspectral IR all-sky radiative transfer model (HIRTM). The simulated GEO CrIS radiances are validated and the hybrid OSSE system is verified before the impact assessment. Two LSS cases from 2018 and 2019 are selected to evaluate the value-added impacts from the GEO CrIS-FSR data. The impact studies show improved atmospheric temperature, moisture, and precipitation forecasts, along with some improvements in the wind forecasts. An added-value, consisting of an overall 5% Root Mean Square Error (RMSE) reduction, was found when a GEO CrIS-FSR is used in replacement of LEO ones indicating the potential for applications of data from a GEO hyperspectral IR sounder to improve local severe storm forecasts.

Buried fault identification in plains is one of the important and difficult problems in current active fault research. Seismic activity forces crustal fluid to migrate up, especially along faults, thereby altering the geochemical characteristics of faults. Hyperspectral remote sensing has an extremely high spectral resolution; data derived from hyperspectral remote sensing have the capacity to detect physicochemical characteristics for mining or the subtle recognition of different underground objects. It provides a new method to detect changes in the geochemical characteristics in the fault. This study is trying to locate the fault by spectrum feature. The Xiadian fault was chosen as the study area. Several samples across the fault were collected, and these samples were measured by an ASD Field Spec 3 spectrometer(Analytical Spectral Devices, Boulder, USA, produced in 2008). Continuum removal, the spectral classification method and the wavelet transform technique have been used for spectral analysis. It has been shown that the spectrum of soil in the fault zone has some special characteristics that are different from those of the spectrum away from fault. Four special spectral regions, 550–580 ​nm, 600–700 ​nm, 700–800 ​nm and 800–900 ​nm, have been extracted as the singular ranges. These individual ranges could be used for fault location in the plain area. There is weak absorption near 880 ​nm of the sample in the fault, indicating that Fe3+ content plays an important role in fault identification and that the iron valences can indicate the fault environment. This study also found that the spectral anomalies in space could reflect the intensity of active tectonics to a certain extent. Therefore, spectral features have the potential to identify a buried faults. This study is the first to use spectroscopic techniques to analyze active tectonics, and there is a new discovery. This new discovery provides the basis for the application of remote sensing in the study of active tectonics.

A detailed analysis of the acousto-optical effect in biaxial crystals is performed using the examples of thallium tetratioarsenate (Tl3AsS4) and iodic acid (α-HIO3) crystals of rhombic syngony. The optimum cross sections of the crystals are determined for such acousto-optical devices as deflectors and filters. The prospects for using thallium tetratioarsenate crystal to create high-performance acousto-optical deflectors and quasi-collinear filters in the near- and mid-IR ranges are demonstrated. It is established that the spectral resolution of acousto-optical filters based on this variant of diffraction is comparable to the resolution of quasi-collinear filters with the same length of acousto-optical interaction.

To realize the high-precision measurement of available nitrogen in coco-peat substrate, the influences of near-infrared (NIR) spectral data of different spectral resolution and band ranges on the model detection performances were studied. A flame NIR spectrometer and an ANTARIS FT-NIR spectrometer were used to acquire spectral data of short-wave near-infrared (SW-NIR) band (1000–1660 nm), long-wave near-infrared (LW-NIR) band (1660–2500 nm), and NIR band (1000–2500 nm) of coco-peat substrate samples respectively. Then, the models were established based on the original data and various pre-processing data. Furthermore, the effects of spectral resolution and detection band ranges on available nitrogen NIR spectroscopy detection of coco-peat substrate were studied by comparing the modeling results. The spectral resolution and detection band ranges had significant influences on the NIR spectroscopy detection of coco-peat substrate available nitrogen. In comparison, the model with high-resolution LW-NIR band spectral data yielded the best prediction performance. Specifically, the correlation coefficients and root mean squared errors in calibration set and prediction set were 0.999, 0.996, 3.197 mg/100g, and 5.373 mg/100g, respectively. The ratio of prediction to deviation was 10.895. High-resolution spectral data was useful to improve the model performance of the sample available nitrogen NIR spectroscopy prediction, and the LW-NIR band range was the optimal detection band for coco-peat substrate available nitrogen NIR spectroscopy detection. Therefore, the high-resolution LW-NIR band spectrometer was useful to the development of high-precision NIR spectroscopy detection equipment for available nitrogen in coco-peat substrate.

Results obtained from ground-based high spectral resolution measurements of solar IR radiation absorption spectra are analyzed. These measurements have been carried out in Peterhof for different ranges of electromagnetic waves to determine the atmospheric total content of СО2 and its contents in the two atmospheric layers—the troposphere and stratosphere. Two spectral schemes to measure solar spectra within ranges of 2600 and 3100–3300 cm–1 are chosen based on an analysis of errors in measurements using different spectral schemes and comparisons with independent measurements and simulation data. Time variations in the tropospheric and stratospheric contents of СО2 for the 2018–2019 period are studied. Within this period, the ХСО2 values in the troposphere mostly exceed those in the stratosphere, and such an excess reached 5–10 ppm. The reverse situation is observed in summer and early fall, when the ХСО2 values in the stratosphere exceed those in the troposphere, which is associated with photosynthesis processes (absorption of СО2 by vegetation in the troposphere). Comparisons of ground-based measurement results with CAMS simulation data and satellite OCO-2 and ACE data show a good agreement for the total content of СО2 and its tropospheric and stratospheric contents. The errors are within 1% if systematic discrepancies are excluded.

Stationary optical spectrometers with both high spectral resolution and broad bandwidth at 800 nm −900 nm are needed in the high speed biosensing and bioimaging systems. Here we present an integrat...

Dynamic nuclear polarization (DNP)-enhanced magic angle spinning (MAS) nuclear magnetic resonance (NMR) of biological systems is a rapidly growing field. Large signal enhancements make the technique particularly attractive for signal-limited cases, such as studies of complex biological assemblies or at natural isotopic abundance. However, spectral resolution is considerably reduced compared to ambient-temperature non-DNP spectra. Herein, we report a systematic investigation into sensitivity and resolution of 1D and 2D 13C-detected DNP MAS NMR experiments on HIV-1 CA capsid protein tubular assemblies. We show that the magnitude and sign of signal enhancement as well as the homogeneous line width are strongly dependent on the biradical concentration, the dominant polarization transfer pathway, and the enhancement buildup time. Our findings provide guidance for optimal choice of sample preparation and experimental conditions in DNP experiments.

Previous work has argued that atomic gas mass estimates of galaxies from 21 cm HI emission are systematically low due to a cold opaque atomic gas component. If true, this opaque component necessitates a ~35% correction factor relative to the mass from assuming optically-thin HI emission. These mass corrections are based on fitting HI spectra with a single opaque component model that produces a distinct "top-hat" shaped line profile. Here, we investigate this issue using deep, high spectral resolution HI VLA observations of M31 and M33 to test if these top-hat profiles are instead superpositions of multiple HI components along the line-of-sight. We fit both models and find that >80% of the spectra strongly prefer a multi-component Gaussian model while, Accepted in MNRAS. 25 pg, 13 figures

In this study, an airborne alpha detection system, which consists of a passivated implanted planar silicon (PIPS) detector and an air filter, was developed. A collimator applied to the alpha detection system showed an enhancement in resolution and a degradation in detection efficiency. The resolution and detection efficiency were compared and analyzed to evaluate the performance of the collimator. Thus, the resolution was found to be more important than the efficiency as a determining factor of the detection system performance, from the viewpoint of radionuclide identification. The performance was evaluated on three properties of the collimator: hole shape, hole length, and the ratio between the hole and frame pitches. From the hole shape performance evaluation, a hexagonal collimator showed the highest resolution. Further, the collimator with a hole pitch of 14 mm was found to have the highest resolution while that with a frame pitch of 4–6 mm (i.e., 1.2–1.4 times longer than the hole pitch) showed the highest resolution.

The 2 m-aperture Survey Space Telescope (also known as the China Space Station Telescope, CSST) is a major science project of China Manned Space Program. It is expected to start science operations around 2024 and has a nominal mission lifetime of 10 years. During observations, CSST will fly independently in the same orbit as the space station while maintaining a large distance apart. It can dock with the space station for refueling and servicing as scheduled or as needed. With a Cook-type three-mirror anastigmat design, CSST can achieve superior image quality within a large field of view (FoV), which gives it an advantage for survey observations. Being an off-axis telescope without any obstruction, its point spread function (PSF) is not affected by diffraction of mirror support structures and is thus helpful for weak-lensing shear measurements. The radius encircling 80% energy of the PSF within CSST’s central 1.1 square degrees of FoV is required to be no more than 0.15″, including all wavefront errors in the optics and instruments and dynamical effects such as the telescope’s attitude control and vibration. CSST will be launched with 5 first-generation instruments including a survey camera, a terahertz receiver, a multichannel imager, an integral field spectrograph, and a cool planet imaging coronagraph. The survey camera is equipped with 30 9k×9k detectors for science observations, each with a filter or grating mounted above, a defocused 9k×9k detector for flux calibration in r band, 8 640×512 near-infrared detectors, fine guide sensors, and wavefront sensors. The primary task of CSST is to carry out a high-resolution large-area multiband imaging and slitless spectroscopy survey covering the wavelength range of 255–1000 nm. Precision cosmology is the main science driver of the survey, and, therefore, the main area of sky selected for observation is at median-to-high galactic latitude and median-to-high ecliptic latitude. It will take the survey camera roughly 7 years of operation accumulated over 10 years of orbital time to image roughly 17500 square degrees of the sky in NUV, u, g, r, i, z, and y bands and take slitless spectroscopy of the same sky in 3 bands. The point-source 5σ limiting magnitudes in g and r bands can reach 26 (AB mag) or higher. The spectral resolution ( R = λ /Δ λ ) of the slitless spectrograph is specified to be on average no less than 200, and the wide-band-equivalent limiting magnitudes in GV (400–620 nm) and GI (620–1000 nm) bands will reach 23 or higher. In addition, a number of deep fields will be selected for more observations to reach at least one magnitude deeper than the wide-area survey. The combined advantage of its angular resolution, depth, wavelength range, capability of both imaging and spectroscopy and large-area sky coverage makes the CSST survey highly competitive, and, at the same time, its observations are also highly complementary with other large projects of its time, such as Vera Rubin Observatory, Euclid, and Roman Space Telescope. These projects will provide extremely rich datasets for potential breakthroughs in studies from the solar system to cosmology and beyond.

Compact and low-cost opto-biomedical sensing systems today are ubiquitously available for measuring the oxygen saturation in blood. The oxygen saturation is derived by a complex, usually not well defined analytical process from the optical absorption of tissue at different wavelengths. The amount of information, which is originally contained in absorption measurements, is drastically reduced by this circumstance. However, the reliability of the analytical process as well as the influence of external parameters like blood pressures on the experimental uncertainty of such systems are widely unknown. Thus, to explore the experimental uncertainty quantitatively, original experimental data have to be used. In commercial systems, however, these data are usually not accessible. Therefore, test systems with full access to original absorption data are necessary. In this work, we develop and describe a test system consisting of color filters and a charge-coupled device (CCD) image sensor, which has substantial advantages in comparison to usually used systems based on multi-color light-emitting diodes (LEDs). Color filters with well-defined filter functions allow for a higher spectral resolution, and will finally guide the way to multi-spectral analysis of blood absorption measurements with reduced uncertainty.

Dusty, neutral outflows and inflows are a common feature of nearby star-forming galaxies. We characterize these flows in eight galaxies -- mostly AGN -- selected for their widespread NaI D signatures from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). This survey employs deep, wide field-of-view integral field spectroscopy at moderate spectral resolution (R=7000 at NaI D). We significantly expand the sample of sightlines in external galaxies in which the spatially-resolved relationship has been studied between cool, neutral gas properties -- N(NaI), Weq(NaI D) -- and dust -- E(B-V) from both stars and gas. Our sample shows strong, significant correlations of total Weq with E(B-V)_stars and g-i colour within individual galaxies; correlations with E(B-V)_gas are present but weaker. Regressions yield slope variations from galaxy to galaxy and intrinsic scatter ~1 Angstrom. The sample occupies regions in the space of N(NaI) and Weq^abs vs. E(B-V)_gas that are consistent with extrapolations from other studies to higher colour excess [E(B-V)_gas ~ 1]. For perhaps the first time in external galaxies, we detect inverse P Cygni profiles in the NaI D line, presumably due to inflowing gas. Via Doppler shifted NaI D absorption and emission lines, we find ubiquitous flows that differ from stellar rotation by >100 km/s or have |v,abs - v,em| > 100 km/s. Inflows and outflows extend toward the edge of the detected stellar disk/FOV, together subtend 10-40% of the projected disk, and have similar mean N(NaI) and Weq(NaI D). Outflows are consistent with minor-axis or jet-driven flows, while inflows tend toward the projected major axis. The inflows may result from non-axisymmetric potentials, tidal motions, or halo infall., MNRAS, in press

—A method is described for recording X-rays with a spectral resolution of λ/Δλ ≈ 20 in five spectral channels in the 0.15–1.0 keV energy range and a time resolution of ∼30 ps based on multilayer X-ray mirrors and an X-ray electron-optical streak camera. The technique is used to register the dynamics of the formation of the X-ray radiation field in the converter cavity.

A way of calculating the field of solar radiation in Earth’s atmosphere is described that considers the thermodynamic non-equilibrium in the vibrational bands of CO2 and O3. The proposed technique allows calculations with high spectral resolution (line by line), along with parameterizations of the optical parameters of the Earth’s upper atmosphere that can be used in calculating the field of solar radiation.

The VIRUS2 instrument is a new fiber-fed multiplexed integral field spectrograph consisting of 6 units, each with 4 spectral channels, to provide large on-sky area coverage coupled with broad spectral coverage. VIRUS2 will be a new facility instrument on the McDonald Observatory 2.7 m Harlan J Smith Telescope. The instrument employs a novel beam-switch module within the fiber feed to split the light into the 4 spectral channels covering 370-930 nm at R~2000, while achieving a very compact and highly stable instrument. The design of VIRUS2 emphasizes stability and careful calibration, with scrambling in the beam-switch module, compact spectrograph format, and tight thermal control. This is the first time such measures have been employed at moderate spectral resolution. In this paper, we provide an overview of the instrument and the build status of the 24 spectrographs, dete ield units. VIRUS2 is funded by NSF and deployment is planned in the second half of 2021.

We designed a compact, real-time LED-based endoscopic imaging system for the detection of various diseases including cancer. In gastrointestinal applications, conventional endoscopy cannot reliably differentiate tumor from normal tissue. Current hyperspectral imaging systems are too slow to be used for real-time endoscopic applications. We are investigating real-time spectral imaging for different tissue types. Our objective is to develop a catheter for real-time hyperspectral gastrointestinal endoscopy. The endoscope uses multiple wavelengths within UV, visible, and IR light spectra generated by a micro-LED array. We capture images with a monochrome micro camera, which is cost-effective and smaller than the current hyperspectral imagers. A wireless transceiver sends the captured images to a workstation for further processing, such as tumor detection. The spatial resolution of the system is defined by camera resolution and the distance to the object, while the number of LEDs in the multi-wavelength light source determines the spectral resolution. To investigate the properties and the limitations of our high-speed spectral imaging approach, we designed a prototype system. We conducted two experiments to measure the optimal forward voltages and lighting duration of the LEDs. These factors affect the maximum feasible imaging rate and resolution. The lighting duration of each LED can be shorter than 10 ms while producing an image with a high signal-to-noise ratio and no illumination interference. These results support the idea of using a high-speed camera and an LED-array for real-time hyperspectral endoscopic imaging.

Current mainstream spectroscopic scintillators for the detection of high-energy radiation are based on inorganic crystals and ceramics, which are difficult to scale up. Efforts have been made to sy...

Herein, a detailed analysis was carried out using high-field (19.9 T) 27Al magic-angle spinning (MAS) nuclear magnetic resonance (NMR) on three specially prepared aluminum oxide samples where the γ-, δ-, and θ-Al2O3 phases are dominantly expressed through careful control of the synthesis conditions. Specifically, two-dimensional (2D) multiquantum (MQ) MAS 27Al was used to obtain high spectral resolution, which provided a guide for analyzing quantitative 1D 27Al NMR spectra. Six aluminum sites were resolved in the 2D MQ MAS NMR spectra, and seven aluminum sites were required to fit the 1D spectra. A set of octahedral and tetrahedral peaks with well-defined quadrupolar line shapes was observed in the θ-phase dominant sample and was unambiguously assigned to the θ-Al2O3 phase. The distinct line shapes related to the θ-Al2O3 phase provided an opportunity for effectively deconvoluting the more complex spectrum obtained from the δ-Al2O3 dominant sample, allowing the peaks/quadrupolar parameters related to the δ-Al2O3 phase to be extracted. The results show that the δ-Al2O3 phase contains three distinct AlO sites and three distinct AlT sites. This detailed Al site structural information offers a powerful way of analyzing the most complex γ-Al2O3 spectrum. It is found that the γ-Al2O3 phase consists of Al sites with local structures similar to those found in the δ-Al2O3 and θ-Al2O3 phases albeit with less ordering. Spin-lattice relaxation time measurement further confirms the disordering of the lattice. Collectively, this study uniquely assigns 27Al features in transition aluminas, offering a simplified method to quantify complex mixtures of aluminum sites in transition alumina samples.

We present a novel airborne imaging differential optical absorption spectroscopy (DOAS) instrument: the Ultraviolet Visible Hyperspectral Imaging Spectrometer (UVHIS), which is developed for trace gas monitoring and pollution mapping. Within a broad spectral range of 200 to 500 nm and operating in three channels, the spectral resolution of UVHIS is better than 0.5 nm. The optical design of each channel comprises a fore-optics with a field of view (FOV) of 40∘, an Offner imaging spectrometer and a charge-coupled device (CCD) array detector of 1032×1072 pixels. A first demonstration flight using UVHIS was conducted on 23 June 2018, above an area of approximately 600 km2 in Feicheng, China, with a spatial resolution of about 25 m×22 m. Measurements of nadir backscattered solar radiation of channel 3 are used to retrieve tropospheric vertical column densities (VCDs) of NO2 with a mean total error of 3.0×1015 molec cm−2. The UVHIS instrument clearly detected several emission plumes transporting from south to north, with a peak value of 3×1016 molec cm−2 in the dominant one. The UVHIS NO2 vertical columns are consistent with the ground-based mobile DOAS observations, with a correlation coefficient of 0.65 for all co-located measurements, a correlation coefficient of 0.86 for the co-located measurements that only circled the steel factory and a slight underestimation for the polluted observations. This study demonstrates the capability of UVHIS for NO2 local emission and transmission monitoring.

The objective of the multispectral pansharpening scheme is to obtain high spatial-spectral resolution multispectral (MS) images using high spectral resolution MS and high spatial resolution panchro...

We demonstrate the application of mode-locked mid-infrared dual frequency comb spectroscopy for combustion analysis. With two settings of the same dual-comb system, the measurement spans 1500 cm−1 from 2.8 to 5 µm with 0.0067 cm−1 (200 MHz) point spacing, or almost a quarter-million discrete comb modes. Using this broadband spectrometer, we quantify the pyrolysis and smoldering combustion of wood samples. Specifically, we measure 20-second time-resolved mole fractions of CH4, H2O, two isotopologues of CO2 (12C16O2, 13C16O2), two isotopologues of CO (12C16O, 13C16O), ethane, formaldehyde, methanol, formic acid, as well as gas temperature directly above radiatively heated wood samples. The combination of the fine spectral resolution and the broad bandwidth of the dual-comb spectrometer allows for precise separation of absorption signatures of individual molecules from the congested spectra.