Low Spectral Resolution Research Articles

GA-NIFS: JWST/NIRSpec IFS view of the z~3.5 galaxy GS5001 and its close environment at the core of a large-scale overdensity

We present JWST Near-Infrared Spectrograph (NIRSpec) observations in integral field spectroscopic (IFS) mode of the galaxy GS5001 at redshift z=3.47, the central member of a candidate protocluster in the GOODS-S field. The data cover a field of view (FoV) of $4 kpc$^2$) and were obtained as part of the Galaxy Assembly with NIRSpec IFS (GA-NIFS) GTO programme. The observations include both high (Rsim 2700) and low (Rsim 100) spectral resolution data, spanning the rest-frame wavelength ranges 3700-6780 and 1300-11850 respectively. These observations enable the detection and mapping of the main optical emission lines from to We analysed the spatially resolved ionised gas kinematics and interstellar medium properties, including obscuration, gas metallicity, excitation, ionisation parameter, and electron density. In addition to the main galaxy (GS5001), the NIRSpec FoV covers a close companion in the south, with three sub-structures with velocities blueshifted by $ with respect to GS5001, and another source in the north redshifted by $ Optical line ratio diagnostics indicate star formation ionisation and electron densities of $ $ across all sources in the FoV. The gas-phase metallicity in the main galaxy is 12+log(O/H) $= 8.45 and slightly lower in the companions (12+log(O/H)$ = 8.34-8.42$), consistent with the mass-metallicity relation at $z We find peculiar line ratios (high log $, low log $) in the northern part of GS5001. These could be attributed to either higher metallicity, or to shocks resulting from the interaction of the main galaxy with the northern source. We identify a spatially resolved outflow in the main galaxy, traced by a broad symmetric component in and with an extension of about 3 kpc. We find maximum outflow velocities of $ an outflow mass of $(1.7 a mass outflow rate of $23 and a mass loading factor of 0.23. These properties are compatible with star formation being the driver of the outflow. Our analysis of these JWST NIRSpec IFS data therefore provides valuable, unprecedented insights into the interplay between star formation, galactic outflows, and interactions in the core of a $z 3.5$ candidate protocluster.

Fiducial Reference Measurement for Greenhouse Gases (FRM4GHG)

The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks.

Assessing the Capacity of High-resolution Commercial Satellite Imagery for Grapevine Downy Mildew Detection and Surveillance in New York state.

Grapevine downy mildew (GDM), caused by the oomycete Plasmopara viticola, can cause 100% yield loss and vine death under conducive conditions. High resolution multispectral satellite platforms offer the opportunity to track rapidly spreading diseases like GDM over large, heterogeneous fields. Here, we investigate the capacity of PlanetScope (3 m) and SkySat (50 cm) imagery for season-long GDM detection and surveillance. A team of trained scouts rated GDM severity and incidence at a research vineyard in Geneva, NY, USA from June to August of 2020, 2021, and 2022. Satellite imagery acquired within 72 hours of scouting was processed to extract single-band reflectance and vegetation indices (VIs). Random forest models trained on spectral bands and VIs from both image datasets could classify areas of high and low GDM incidence and severity with maximum accuracies of 0.85 (SkySat) and 0.92 (PlanetScope). However, we did not observe significant differences between VIs of high and low damage classes until late July-early August. We identified cloud cover, image co-registration, and low spectral resolution as key challenges to operationalizing satellite-based GDM surveillance. This work establishes the capacity of spaceborne multispectral sensors to detect late-stage GDM and outlines steps towards incorporating satellite remote sensing in grapevine disease surveillance systems.

A new dimension in the variability of AGB stars: Convection patterns size changes with pulsation

Context. Stellar convection plays an important role in atmospheric dynamics, wind formation, and the mass-loss processes in asymptotic giant branch stars. However, a direct characterization of convective surface structures in terms of size, contrast, and lifespan is quite challenging, as spatially resolving these features requires the highest angular resolution. Aims. We aim to characterize the size of convective structures on the surface of the O-rich AGB star R Car to test different theoretical predictions based on mixing-length theory from solar models. Methods. We used infrared low-spectral resolution (R ∼ 35) interferometric data in the H-band (∼1.76 μm) obtained by the instrument PIONIER at the Very Large Telescope Interferometer (VLTI) to image the star’s surface at two epochs separated by approximately six years. Using a power spectrum analysis, we estimated the horizontal size of the structures on the surface of R Car. The sizes of the stellar disk at different phases of a pulsation cycle were obtained using parametric model fitting in the Fourier domain. Results. Our analysis supports that the sizes of the structures in R Car are correlated with variations in the pressure scale height in the atmosphere of the target, as predicted by theoretical models based on solar convective processes. We observed that these structures grow in size when the star expands within a pulsation cycle. While the information is still scarce, this observational finding highlights the role of convection in the dynamics of those objects. New interferometric imaging campaigns with the renewed capabilities of the VLTI are envisioned to expand our analysis to a larger sample of objects.

A Retrospective Study: Are the Multi-Dips in the THz Spectrum during Laser Filamentation Caused by THz–Plasma Interactions?

During the process of terahertz (THz) wave generation via femtosecond laser filamentation in air, as well as through the mixing of THz waves with externally injected plasma filaments, THz waves engage in interactions with the plasma. A characteristic feature of this interaction is the modulation of the THz radiation spectrum by the plasma, which includes the generation of THz spectral dips. This information is essential for understanding the underlying mechanisms of THz–plasma interactions or for inferring plasma parameters. However, a current debate exists on the number of THz spectral dips observed after the interaction, with different opinions of single versus multiple dips, thus leaving the interaction mechanisms still ambiguous. In this work, we retrospectively analyzed the experimental appearance of multiple dips in the THz spectrum and found that the current observations of such dips are predominantly a result of the water vapor absorption with a low spectral resolution. Additionally, we observed that altering the acquisition width of the temporal THz signal also influenced the dips’ number. Hence, in future research, simultaneous attention should be paid to the following two aspects of THz–plasma interactions: (1) It is necessary to ensure a sufficiently wide time-domain window to accurately represent the spectral dip characteristics. (2) The spectral dips should be carefully distinguished from the water absorption lines before being further studied. On the other hand, for the case of a single dip in the THz spectrum, we also put forward a new viewpoint of the resonance between surface plasmon waves and THz waves, which should also be taken into consideration in future studies.

An impressionist view of V Hydrae

Context. Asymptotic giant branch (AGB) stars enrich the interstellar medium through their mass loss. The mechanism(s) shaping the circumstellar environment of mass-losing stars is not clearly understood so far. Aims. Our purpose is to study the effect of binary companions located within the first 10 stellar radii from the primary AGB star. In this work, we target the mass-losing carbon star V Hydrae (V Hya) and search for signatures of its companion in the dust-forming region of the atmosphere. Methods. The star was observed in the L and N bands with the VLTI/MATISSE instrument at low spectral resolution. We reconstructed images of the photosphere and surroundings of V Hya using the two bands and compared our interferometric observables with VLTI/MIDI and VISIR archival data. To constrain the dust properties, we used the 1D radiative transfer code DUSTY to model the spectral energy distribution. Results. The star is dominated by dust emission in the L- and N-bands. The MATISSE reconstructed images show asymmetric and elongated structures in both infrared bands. In the L band, we detected an elongated shape of approximately 15 mas that likely is of photospheric origin. In the N band, we found a 20 mas extension northeast from the star and perpendicular to the L-band elongated axis. The position angle and the size of the N-band extension match the prediction of the companion position at the MATISSE epoch. By comparing MATISSE N-band with MIDI data, we deduce that the elongation axis in the N-band has rotated since the previous interferometric measurements 13 yr ago, supporting the idea that the particle enhancement is related to the dusty clump moving along with the companion. The VISIR image confirms the presence of a large-scale dusty circumstellar envelope surrounding V Hya. Conclusions. The MATISSE images unveil the presence of a dust enhancement at the position of the companion. This opens new doors for further analyses of the binary interaction with an AGB component.

ReLAP-Net: Residual Learning and Attention Based Parallel Network for Hyperspectral and Multispectral Image Fusion

Remote sensing applications require high-resolution images to obtain precise information about the Earth???s surface. Multispectral images have high spatial resolution but low spectral resolution. Hyperspectral images have high spectral resolution but low spatial resolution. This study proposes a residual learning and attention-based parallel network based on residual network and channel attention. The network performs image fusion of a high spatial resolution multispectral image and a low spatial resolution hyperspectral image. The network training and fusion experiments are conducted on four public benchmark data sets to show the effectiveness of the proposed model. The fusion performance is compared with classical signal processing???based image fusion techniques. Four image metrics are used for the quantitative evaluation of the fused images. The proposed network improved fusion ability by reducing the root mean square error and relative dimensionless global error in synthesis and increased the peak signal-to-noise ratio when compared to other state-of-the-art models.

Enhancing Micro-Raman Spectroscopy: A Variable Spectral Resolution Instrument Using Zoom Lens Technology.

Raman spectroscopy is a powerful analytical technique based on the inelastic scattering of photons. Conventional macro-Raman spectrometers are suitable for mass analysis but often lack the spatial resolution required to accurately examine microscopic regions of interest. For this reason, the development of micro-Raman spectrometers has been driven forward. However, even with micro-Raman spectrometers, high resolution is required to gain better insight into materials that provide low-intensity Raman signals. Here, we show the development of a micro-Raman spectrometer with implemented zoom lens technology. We found that by replacing a second collimating mirror in the monochromator with a zoom lens, the spectral resolution could be continuously adjusted at different zoom factors, i.e., high resolution was achieved at a higher zoom factor and lower spectral resolution was achieved at a lower zoom factor. A quantitative analysis of a micro-Raman spectrometer was performed and the spectral resolution was analysed by FWHM using the Gaussian fit. Validation was also performed by comparing the results obtained with those of a high-grade laboratory Raman spectrometer. A quantitative analysis was also performed using the ANOVA method and by assessing the signal-to-noise ratio between the two systems.

Detection of microplastics based on splicing grating spatial heterodyne Raman spectroscopy

As a new type of persistent pollutant, microplastics pose a serious threat to the earth’s ecological environment and human health. Efficient and reliable microplastic detection technology is of great significance in the management of microplastic pollution. Aiming at the problems of low signal-to-noise ratio (SNR), narrow spectral range and low spectral resolution in traditional microplastic detection technology, a splicing grating spatial heterodyne Raman spectroscopy (SG-SHRS) is proposed in this paper. The splicing grating is composed of four sub-gratings with groove densities of 320, 298, 276 and 254 gr / mm, respectively. Each sub-grating has an independent sub-filter to improve the SNR of the system. The system is simulated, built and calibrated. The actual resolution of the SG-SHRS system is 0.7 cm−1, and the spectral detection range of a single sub-grating is 2947.2 cm−1. Four kinds of microplastics, polyamide (PA), polystyrene (PS), polycarbonate (PC), and polyphenylene sulfide (PPS), were detected by the SG-SHRS system. The complete Raman spectral information of microplastics was obtained, and the peak assignment of Raman characteristic peaks of the four kinds of microplastics was analyzed. By comparing the test results with a commercial dispersion spectrometer, it has been proven that the SG-SHRS system has the advantages of high spectral resolution, wide spectral range, and high SNR, and has good application prospects in the field of microplastic detection.

Fusion of UNet and ResNet decisions for change detection using low and high spectral resolution images

Fusion of UNet and ResNet decisions for change detection using low and high spectral resolution images

The GRAVITY young stellar object survey

Context. Temporal variability in the photometric and spectroscopic properties of protoplanetary disks is common in young stellar objects. However, evidence pointing toward changes in their morphology over short timescales has only been found for a few sources, mainly due to a lack of high-cadence observations at high angular resolution. Understanding this type of variation could be important for our understanding of phenomena related to disk evolution. Aims. We study the morphological variability of the innermost circumstellar environment of HD 98922, focusing on its dust and gas content. Methods. Multi-epoch observations of HD 98922 at milliarcsecond resolution with VLTI/GRAVITY in the K-band at low (R = 20) and high (R = 4000) spectral resolution are combined with VLTI/PIONIER archival data covering a total time span of 11 yr. We interpret the interferometric visibilities and spectral energy distribution with geometrical models and through radiative transfer techniques using the code MCMax. We investigated high-spectral-resolution quantities (visibilities and differential phases) to obtain information on the properties of the HI Brackett-γ (Brγ)-line-emitting region. Results. Comparing observations taken with similar (u,v) plane coverage, we find that the squared visibilities do not vary significantly, whereas we find strong variability in the closure phases, suggesting temporal variations in the asymmetric brightness distribution associated to the disk. Our observations are best fitted by a model of a crescent-like asymmetric dust feature located at ~1 au and accounting for ~70 % of the near-infrared (NIR) emission. The feature has an almost constant magnitude and orbits the central star with a possible sub-Keplerian period of ~12 months, although a 9 month period is another, albeit less probable, solution. The radiative transfer models show that the emission originates from a small amount of carbon-rich (25%) silicates, or quantum-heated particles located in a low-density region. Among different possible scenarios, we favor hydrodynamical instabilities in the inner disk that can create a large vortex. The high spectral resolution differential phases in the Brγ line show that the hot-gas compact component is offset from the star and in some cases is located between the star and the crescent feature. The scale of the emission does not favor magnetospheric accretion as a driving mechanism. The scenario of an asymmetric disk wind or a massive accreting substellar or planetary companion is discussed. Conclusions. With this unique observational data set for HD 98922, we reveal morphological variability in the innermost 2 au of its disk region. This property is possibly common to many other protoplanetary disks, but is not commonly observed due to a lack of high-cadence observation. It is therefore important to pursue this approach with other sources for which an extended dataset with PIONIER, GRAVITY, and possibly MATISSE is available.

Granite Extraction Based on the SDGSAT-1 Satellite Thermal Infrared Spectrometer Imagery.

Earth observation by remote sensing plays a crucial role in granite extraction, and many current studies use thermal infrared data from sensors such as ASTER. The challenge lies in the low spatial resolution of these satellites, hindering precise rock type identification. A breakthrough emerges with the Thermal Infrared Spectrometer (TIS) on the Sustainable Development Science Satellite 1 (SDGSAT-1) launched by the Chinese Academy of Sciences. With an exceptional 30 m spatial resolution, SDGSAT-1 TIS opens avenues for accurate granite extraction using remote sensing. This study, exemplified in Xinjiang's Karamay region, introduces the BR-ISauvola method, leveraging SDGSAT-1 TIS data. The approach combines band ratio with adaptive k-value selection using local grayscale statistical features for Sauvola thresholding. Focused on large-scale granite extraction, results show F1 scores above 70% for Otsu, Sauvola, and BR-ISauvola. Notably, BR-ISauvola achieves the highest accuracy at 82.11%, surpassing Otsu and Sauvola by 9.62% and 0.34%, respectively. This underscores the potential of SDGSAT-1 TIS data as a valuable resource for granite extraction. The proposed method efficiently utilizes spectral information, presenting a novel approach for rapid granite extraction using remote sensing TIS imagery, even in scenarios with low spectral resolution and a single data source.

The Rossiter-McLaughlin effect and exoplanet transits: A delicate association at medium and low spectral resolution

The characterization of exoplanetary atmospheres via transit spectroscopy is based on the comparison between the stellar spectrum filtered through the atmosphere and the unadulterated spectrum from the occulted stellar region. The disk-integrated spectrum is often used as a proxy for the occulted spectrum, yet they differ along the transit chord depending on stellar type and rotational velocity. This is referred to as the Rossiter-McLaughlin (RM) effect, which is known to bias transmission spectra at high spectral resolution when calculated with the disk-integrated stellar spectrum. Recently, it was shown that the first claimed atmospheric signal from an exoplanet cannot arise from absorption in the core of the sodium doublet, because the features observed at high resolution are well reproduced by the RM effect. However, it remains unclear as to whether the detection made at medium spectral resolution with the HST arises from the smoothed RM signature or from the wings of the planetary absorption line. More generally, the impact of the RM effect at medium and low spectral resolution remains poorly explored. To address this question, we simulated realistic transmission spectra in a variety of systems using the EVaporating Exoplanets code. We find that the Rm effect should not bias broadband atmospheric features, such as hazes or molecular absorption, measured with the JWST/NIRSPEC (prism mode) at low resolution. However, absorption signatures from metastable helium or sodium measured at medium resolution with the JWST/NIRSPEC (G140H mode) or HST/STIS can be biased, especially for planets on misaligned orbits across fast rotators. In contrast, we show that the Na signature originally reported in HD 209458b, an aligned system, cannot be explained by the RM effect, supporting a planetary origin. Contamination by the RM effect should therefore be accounted for when interpreting high- and medium-resolution transmission spectra of exoplanets.

JADES: The emergence and evolution of Lyα emission and constraints on the intergalactic medium neutral fraction

The rest-frame UV recombination emission line Lyα can be powered by ionising photons from young massive stars in star-forming galaxies, but the fact that it can be resonantly scattered by neutral gas complicates its interpretation. For reionisation-era galaxies, a neutral intergalactic medium will scatter Lyα from the line of sight, making Lyα a useful probe of the neutral fraction evolution. Here, we explore Lyα in JWST/NIRSpec spectra from the ongoing JADES programme, which targets hundreds of galaxies in the well-studied GOODS-S and GOODS-N fields. These sources are UV-faint (−20.4 < MUV < −16.4) and thus represent a poorly explored class of galaxy. We fitted the low spectral resolution spectra (R ∼ 100) of a subset of 84 galaxies in GOODS-S with zspec > 5.6 (as derived with optical lines) with line and continuum models to search for significant line emission. Through exploration of the R100 data, we find evidence for Lyα in 17 sources. This sample allowed us to place observational constraints on the fraction of galaxies with Lyα emission in the redshift range 5.6 < z < 7.5, with a decrease from z = 6 to z = 7. We also find a positive correlation between the Lyα equivalent width and MUV, as seen in other samples. We used these results to estimate the neutral gas fraction at z ∼ 7, and our estimates are in agreement with previous results (XHI ∼ 0.5 − 0.9).

A transformer acoustic signal analysis method based on matrix pencil and hybrid deep neural network

Acoustic signal analysis is an important component of transformer online monitoring. Currently, traditional methods have problems such as low spectral resolution, imbalanced sample distribution, and unsatisfactory classification performance. This article first introduces the matrix pencil algorithm for time-frequency spectrum analysis of acoustic signals, and then uses the SMOTE algorithm to expand the imbalanced samples. Then, an ACmix hybrid deep neural network model is constructed to classify 11 types of transformer operation and environmental acoustic signals. Finally, detailed experiments were conducted on the method proposed in this paper, and the experimental results showed that the matrix pencil algorithm has high time-frequency resolution and good noise resistance performance. The SMOTE sample expansion method can significantly improve the recognition accuracy by more than 2%. Overall accuracy of the proposed method in acoustic signal classification tasks reaches 91.81%.

When one equals two: Chemometrics turns Mössbauer spectrometer into X-ray fluorescence one

Here we explore the feasibility of using classical Mössbauer spectroscopy setup in scattering geometry to assess the elemental composition of samples using characteristic X-ray fluorescence. Even though, the scintillation detector of Mössbauer spectrometer yields rather low spectral resolution spectra, this can be effectively compensated using chemometric data processing. This hypothesis was first checked with simulated spectra of steel samples and afterwards was confirmed with real experiments. The results of Ti, Cr, Mn, Ni, Nb and Mo quantification in real steel samples obtained from Mössbauer spectrometer were compared with those obtained with commercial energy dispersive X-ray fluorescence (EDXRF) spectrometer. In case of Ti, Cr and Ni the accuracy attained with Mössbauer spectrometer was similar to that of an ordinary commercial EDXRF device.

Airborne observation with a low-cost hyperspectral instrument: retrieval of NO2 vertical column densities (VCDs) and the satellite sub-grid variability over industrial point sources

Abstract. High-spatial-resolution NO2 vertical column densities (VCDs) were retrieved from airborne observations using the low-cost hyperspectral imaging sensor (HIS) at three industrial areas (i.e., Chungnam, Jecheon, and Pohang) in South Korea, where point sources (i.e., power plant, petrochemical complex, steel yard, and cement kiln) with significant NO2 emissions are located. An innovative and versatile approach for NO2 VCD retrieval, hereafter referred to as the modified wavelength pair (MWP) method, was developed to overcome the excessively variable radiometric and spectral characteristics of the HIS attributed to the absence of temperature control during the flight. The newly developed MWP method was designed to be insensitive to broadband spectral features, including the spectral dependency of surface and aerosol reflectivity, and can be applied to observations with relatively low spectral resolutions. Moreover, the MWP method can be implemented without requiring precise radiometric calibration of the instrument (i.e., HIS) by utilizing clean-pixel data for non-uniformity corrections and is also less sensitive to the optical properties of the instrument and offers computational cost competitiveness. In the experimental flights using the HIS, NO2 plumes emitted from steel yards were particularly conspicuous among the various NO2 point sources, with peak NO2 VCDs of 2.0 DU (Dobson unit) at Chungnam and 1.8 DU at Pohang. Typical NO2 VCD uncertainties ranged between 0.025–0.075 DU over the land surface and 0.10–0.15 DU over the ocean surface, and the discrepancy can be attributable to the lower signal-to-noise ratio over the ocean and higher sensitivity of the MWP method to surface reflectance uncertainties under low-albedo conditions. The NO2 VCDs retrieved from the HIS with the MWP method showed a good correlation with the collocated Tropospheric Monitoring Instrument (TROPOMI) data (r=0.73, mean absolute error equals 0.106 DU). However, the temporal disparities between the HIS frames and the TROPOMI overpass, their spatial mismatch, and their different observation geometries could limit the correlation. The comparison of TROPOMI and HIS NO2 VCDs further demonstrated that the satellite sub-grid variability could be intensified near the point sources, with more than a 3-fold increase in HIS NO2 VCD variability (e.g., difference between 25th and 75th quantiles) over the TROPOMI footprints with NO2 VCD values exceeding 0.8 DU compared to footprints with NO2 VCD values below 0.6 DU.

Metalens-Based Compressed Ultracompact Femtophotography: Analytical Modeling and Simulations

Single-shot 2-dimensional optical imaging of transient phenomena is indispensable for numerous areas of study. Among existing techniques, compressed ultrafast photography (CUP) using a chirped ultrashort pulse as active illumination can acquire nonrepetitive time-evolving events at hundreds of trillions of frames per second. However, the bulky size and conventional configurations limit its reliability and application scopes. Superdispersive metalenses offer a promising solution for an ultracompact design with a stable performance by integrating the functions of a focusing lens and dispersive optical components into a single device. Nevertheless, existing metalens designs, typically optimized for the full visible spectrum with a relatively low spectral resolution, cannot be readily applied to active-illumination CUP. To address these limitations, here, we propose single-shot compressed ultracompact femtophotography (CUF) that synergically combines the fields of nanophotonics, optical imaging, compressed sensing, and deep learning. We develop the theory of CUF’s data acquisition composed of temporal–spectral mapping, spatial encoding, temporal shearing, and spatiotemporal integration. We also develop CUF’s image reconstruction via deep learning. Moreover, we design and evaluate CUF’s crucial components—a static binary transmissive mask, a superdispersive metalens, and a 2-dimensional sensor. Finally, using numerical simulations, CUF’s feasibility is verified using 2 synthetic scenes: an ultrafast beam sweeping across a surface and the propagation of a terahertz Cherenkov wave.

Polarization transfer methods for quantitative analysis of flowing mixtures with benchtop 13C NMR spectroscopy.

Benchtop NMR spectroscopy is attractive for process monitoring; however, there are still drawbacks that often hamper its use, namely, the comparatively low spectral resolution in 1H NMR, as well as the low signal intensities and problems with the premagnetization of flowing samples in 13C NMR. We show here that all these problems can be overcome by using 1H-13C polarization transfer methods. Two ternary test mixtures (one with overlapping peaks in the 1H NMR spectrum and one with well-separated peaks, which was used as a reference) were studied with a 1T benchtop NMR spectrometer using the polarization transfer sequence PENDANT (polarization enhancement that is nurtured during attached nucleus testing). The mixtures were analyzed quantitatively in stationary as well as in flow experiments by PENDANT enhanced 13C NMR experiments, and the results were compared with those from the gravimetric sample preparation and from standard 1H and 13C NMR spectroscopy. Furthermore, as a proxy for a process monitoring application, continuous dilution experiments were carried out, and the composition of the mixture was monitored in a flow setup by 13C NMR benchtop spectroscopy with PENDANT. The results demonstrate the high potential of polarization transfer methods for applications in quantitative process analysis with benchtop NMR instruments, in particular with flowing samples.

IMPACT OF UAV AND SENTINEL-2A IMAGERY FUSION ON VEGETATION INDICES PERFORMANCE

Abstract. Image fusion techniques can improve the quality of remote sensing images by combining high spatial resolution images with low spectral resolution images. This enhancement of the images may impact the performance of various vegetation indices (VI’s). This study investigates the impact of image fusion on the quality of vegetation indices by fusing UAV (Unmanned Aerial Vehicle) bands with Sentinel-2A images using Principal Component Analysis (PCA) and Brovery Transform (BT) fusion techniques.The fused images were used to calculate the Normalized Difference Vegetation Index, Normalized Difference Red Edge, Green Red Vegetation Index, and Normalized Difference Water Index. To assess the performance of the fused images, several image quality assessment metrics were used, including Root Mean Square Error (RMSE), Entropy, etc...The results showed that image fusion techniques can improve the quality of images which is important to assess crop health. The PCA image fusion technique showed higher quality than the BT technique. The PCA fused images had lower RMSE, ERGAS, and Entropy Difference and higher UIQI, CC, and SSIM values than the original images. Moreover, the fused images produced higher VIs values than the Sentinel-2A images.Finally, scatter plots were created to compare the correlation between the VIs calculated from the original and fused images. The results showed a strong correlation between the VIs calculated from the Sentinel-2A and fused images, indicating that the fused images can accurately estimate vegetation health parameters. Overall, this study demonstrates the potential of image fusion techniques to improve the quality of VI’s for monitoring vegetation health.