Spectral Scale Research Articles

Compression of the laser pulse in magnetized plasma having relativistic regime

A study of the interaction of laser with magnetized plasma in the relativistic regime has been presented. Using Maxwell equations, a modified nonlinear Schrodinger equation (MNLS) is derived for nonlinear propagation of the laser pulse in the presence of a magnetic field (where the propagation of laser pulse is along magnetic field). Using the pseudospectral and finite difference methods the (MNLS) equation has been solved numerically for typical laser plasma parameters. It is found that the compression of the ultra-short laser pulse is enhanced by application of static magnetic field and the laser pulse is gradually compressed from 30 to 12fs. We have also observed the splitting of the laser pulse inside the plasma and the generation of magnetic turbulence. The ensemble averaged power spectrum of magnetic turbulence has been presented. Our results follow the spectral index approximation scales, of the order of k−2 at larger scale and k−4 at a smaller scale. Such a nonlinear interaction is quite important in understanding turbulence in the astrophysical phenomenon.

A spectral method for fast sensitivity analysis: Perfectly stirred reactors

A new spectral method is proposed to speedup sensitivity analysis (SA) for ignition and extinction of perfectly stirred reactors (PSR). The method takes advantage of the linear dependency in the stoichiometric coefficient vectors of the elementary reactions in detailed kinetic mechanisms. Compared with the conventional SA that needs to perturb each elementary reaction, the spectral method lumps the elementary reactions into a smaller set of semi-global reactions that are basis vectors for the elementary reaction set, and perturbs each semi-global reaction instead. The sensitivities for the elementary reactions are then computed as linear combinations of the sensitivities for the semi-global reactions. As a result, the computational cost of the spectral method scales as the number of species, while that of the conventional method scales as the number of reactions. The proposed method is demonstrated for PSR extinction using a detailed H2 mechanism.

Large-Scale and Multiscale Networks in the Rodent Brain during Novelty Exploration.

Neural activity is coordinated across multiple spatial and temporal scales, and these patterns of coordination are implicated in both healthy and impaired cognitive operations. However, empirical cross-scale investigations are relatively infrequent, because of limited data availability and to the difficulty of analyzing rich multivariate datasets. Here, we applied frequency-resolved multivariate source-separation analyses to characterize a large-scale dataset comprising spiking and local field potential (LFP) activity recorded simultaneously in three brain regions (prefrontal cortex, parietal cortex, hippocampus) in freely-moving mice. We identified a constellation of multidimensional, inter-regional networks across a range of frequencies (2–200 Hz). These networks were reproducible within animals across different recording sessions, but varied across different animals, suggesting individual variability in network architecture. The theta band (∼4–10 Hz) networks had several prominent features, including roughly equal contribution from all regions and strong inter-network synchronization. Overall, these findings demonstrate a multidimensional landscape of large-scale functional activations of cortical networks operating across multiple spatial, spectral, and temporal scales during open-field exploration.

Spectrum calibration of the first hyperspectral infrared measurements from a geostationary platform: Method and preliminary assessment

AbstractThe level‐1 (L1) radiance spectra from the first Geostationary Interferometric InfraRed Sounder (GIIRS) have been publicly available since January 2019. On account of the inherent observation characteristics, operation modes, and capabilities, a complete spectrum calibration method of GIIRS/L1 products is originally proposed to form the latest version (V3) algorithm for implementation. Particularly, four targeted improvements in three aspects are independently established: subsample location alignment to yield integrated interferograms in both forward and backward directions with almost zero phase, rough spectral scale unification as well as accurate spectral scale correction to resolve spectral non‐uniformity due to a seriously asymmetric configuration of focal plane array, and an additional double‐reflected compensation to mitigate the influence of non‐ideal onboard blackbody reference upon radiometric accuracy. Preliminary assessments from both domestic and international sources indicate that the spectral and radiometric accuracies of the measured spectra from the latest GIIRS/L1 V3 algorithm show a well‐behaved performance in both longwave (LW) and midwave (MW) bands, that is, lower than 10 ppm of spectral scale errors, which is of sufficient accuracy for numerical weather prediction use, and around 1 K for most uncontaminated channels within the LW band. However, non‐linearity correction of interferograms and spectral quality improvements, especially for the MW band, should be developed further. In general, a feasible solution of spectrum calibration for a hyperspectral sounder on geostationary platform is provided in detail for reference, which is expected to benefit users of GIIRS data as well as designers responsible for L1 data processing of other similar sensors.

Assessment of Equivalence of the Spectral Radiance Scales Following the Results of the Comparison between the National Metrology Institutes of Korea, China, and Russia

The paper presents the assessment of equivalence of the spectral radiance scales in the wavelength range from 250 to 2500 nm, reproduced at the national metrology institutes of Korea (KRISS), China (NIM), and Russia (VNIIOFI), carried out in the framework of international comparisons. The common set of three tungsten strip lamps was used as an artefact. Based on a series of blind measurements of the lamps spectral radiance performed at each laboratory alternately, the reference value of the comparison was determined at each wavelength as a weighted mean of the measured data of three laboratories. The degree of equivalence of each laboratory was then calculated as the deviation of the measurement data of that participant from the reference value. A data analysis method was proposed for calculating the degree of equivalences and their uncertainties. The method is based on processing spectral radiance ratios, rather than differences, which allows eliminating the influence of a result of one particular participant to results of other laboratories. The comparison results confirm the equivalence of spectral radiance scales of all the laboratories within their expanded uncertainties (k = 2) except a few wavelength points.

Influence of optical radiation on the silver nanoparticles formation

In this work, the synthesis of spherical silver nanoparticles in aqueous solution was performed by photostimulated reduction. A research of the laser exposure time effect of silver colloids on the optical response and nanoparticles concentration in the studied solution was carried out. The influence of long time exposure (up to 6 days) of silver colloid by LEDs with radiation wavelengths of 525 and 633 nm on their geometric, spatial and optical parameters was studied. It has been shown that prolonged irradiation of silver colloid leads to changes in the nanoparticles morphology, which is confirmed by a change in the colloidal color and appearance of additional plasmon absorption peaks on the spectral scale. The formation of silver nanoparticles and nanoprisms in aqueous solution was confirmed by spectrophotometry and transmission electron microscopy. Modelling of absorption spectra of triangular silver nanoparticles by the discrete dipole approximation approach, implemented in DDSCAT software, was carried out.. The electromagnetic radiation of the optical range is a promising tool that can be effectively used for both synthesis and modification of optical and spatial parameters of silver nanoparticles.

Mid-infrared spectral responsivity scale based on an absolute cryogenic radiometer and a tunable quantum cascade laser

The spectral optical radiant power of a quantum cascade laser (QCL) in the (7.35–10.6) µm spectral range has been measured using a Y-shape absolute cryogenic radiometer (ACR). The spectral responsivity (SR) of a transfer detector based on an integrating-sphere-coupled mercury-cadmium-telluride (IS-MCT) photoconductive detector has been calibrated. The optical radiant power of the QCL can be adjusted and stabilized in the range of (0.035–0.6) mW. The relative uncertainty of the ACR-based optical radiant power measurement was evaluated to be 0.023%–0.04% (k = 1). The relative uncertainty of the SR calibration of the IS-MCT transfer detector was analyzed to be 0.097%–0.16% (k = 1). The spectral range for the SR calibration can be extended to cover (3–12) µm using commercially available QCLs.

Reflectometers for Absolute and Relative Reflectance Measurements in the Mid-IR Region at Vacuum.

We demonstrated spectral reflectometers for two types of reflectances, absolute and relative, of diffusely reflecting surfaces in directional-hemispherical geometry. Both are built based on the integrating sphere method with a Fourier-transform infrared spectrometer operating in a vacuum. The third Taylor method is dedicated to the reflectometer for absolute reflectance, by which absolute spectral diffuse reflectance scales of homemade reference plates are realized. With the reflectometer for relative reflectance, we achieved spectral diffuse reflectance scales of various samples including concrete, polystyrene, and salt plates by comparing against the reference standards. We conducted ray-tracing simulations to quantify systematic uncertainties and evaluated the overall standard uncertainty to be 2.18% (k = 1) and 2.99% (k = 1) for the absolute and relative reflectance measurements, respectively.

Understanding Vine Hyperspectral Signature through Different Irrigation Plans: A First Step to Monitor Vineyard Water Status

The main challenge encountered by Mediterranean winegrowers is water management. Indeed, with climate change, drought events are becoming more intense each year, dragging the yield down. Moreover, the quality of the vineyards is affected and the level of alcohol increases. Remote sensing data are a potential solution to measure water status in vineyards. However, important questions are still open such as which spectral, spatial, and temporal scales are adapted to achieve the latter. This study aims at using hyperspectral measurements to investigate the spectral scale adapted to measure their water status. The final objective is to find out whether it would be possible to monitor the vine water status with the spectral bands available in multispectral satellites such as Sentinel-2. Four Mediterranean vine plots with three grape varieties and different water status management systems are considered for the analysis. Results show the main significant domains related to vine water status (Short Wave Infrared, Near Infrared, and Red-Edge) and the best vegetation indices that combine these domains. These results give some promising perspectives to monitor vine water status.

Development of a detector-based absolute spectral power responsivity scale in the spectral range of 300–1600 nm

The radiometry laboratory at the National Institute of Standards (NIS) has taken in his shoulder to develop and improve the spectral responsivity facilities to get high precision and more reliable optical detectors measurements. During the last few years, the calibration of the detectors was refined as well as the reliability of spectral responsivity results, especially in the critical ultra-violet and infrared range of the spectrum. This setup was constructed using a lamp-monochromator-based setup accompanied by a silicon trap detector and an Indium Gallium Arsenide (InGaAs) detector to extend the scale to the infrared (IR) spectral region. Both detectors are traceable and shown to be spatially uniform, linear, stable, and capable of disseminating an absolute spectral responsivity scale. The uncertainty contribution of the spectral responsivity for a silicon-based detector is less than 1–1.9% for the spectral range 300–1100 nm, and about 2–3.8 % (k = 2) for InGaAs-based detector in the wavelength range 800–1600 nm. Additionally, this paper gives a comprehensive overview of’ NIS’s spectral responsivity facilities, which are now fully automated and controlled by LabVIEW.

Technological opportunities for sensing of the health effects of weather and climate change: a state-of-the-art-review.

Sensing and measuring meteorological and physiological parameters of humans, animals, and plants are necessary to understand the complex interactions that occur between atmospheric processes and the health of the living organisms. Advanced sensing technologies have provided both meteorological and biological data across increasingly vast spatial, spectral, temporal, and thematic scales. Information and communication technologies have reduced barriers to data dissemination, enabling the circulation of information across different jurisdictions and disciplines. Due to the advancement and rapid dissemination of these technologies, a review of the opportunities for sensing the health effects of weather and climate change is necessary. This paper provides such an overview by focusing on existing and emerging technologies and their opportunities and challenges for studying the health effects of weather and climate change on humans, animals, and plants.

Флуоресцентные свойства гуминовых кислот почв разных условий формирования

The purpose of the study. To identify the features of humic acids of soils of different formation conditions using quantitative indicators of fluorescence spectra. Place and time of the event. The research was carried out on the territory of Siberia, where in the period 2000-2021, key areas with different natural conditions were identified in different regions. Methodology. Humic acids (HA) are considered as an independent component of the system of humus substances (SHS) of soils, the properties of which depend on the ecological conditions of formation. Soil samples were taken during the period of the most stable state of the system of humus substances in a continuous column every 5–10 cm and (or) less within the visible boundaries of genetic horizons. The HA preparations were isolated with 0.1 n NaOH after preliminary soil decalcification followed by precipitation with 2 n HCl. Additional purification from ash elements was not carried out. Fluorescence spectra of humic acid solutions with the same concentration of the substance (0.01 % HA) at pH of 13 were recorded in the wavelength range of 300–650 nm on an Agilen Cary Eclipse Fluorescence Spectrophotometer at an excitation wavelength of 330 nm. The main results. The average statistical quantitative indicators of the fluorescence spectra of humic acids of soils formed under different natural conditions were calculated: the position of the fluorescence maximum (λmax), the value of the first moment (M1), and the ratio of the integral fluorescence intensities in the areas of its maximum manifestation in the red and blue parts of the spectrum (coefficient α). The results showed that soils formed in different natural conditions have different ranges of values of all quantitative indicators of the fluorescent properties of humic acids. They differ significantly in tundra soils of plain and mountainous conditions, within the same mountainous country due to vertical zonality, within the same territory with ring zonality due to the change of humidification areas, and with other qualitative differences in the natural environment forming them. It is shown that M1 reflects the configuration features of humic acids due to the conditions of soil formation, while the coefficient α reflects the state of this soil component during the period of soil sampling depending on the local conditions of their functioning. Conclusion. The analysis of quantitative parameters of the fluorescence spectra of humic acids of soils of different conditions of formation made it possible, using emission spectra at one excitation wavelength (330 nm), to identify the specifics of the fluorescent properties of humic acids, which manifests itself in the position of the fluorescence maximum on the spectral scale, the value of the first moment and the ratio of the values of integral intensities in the long-wave and short-wave spectral regions. The data showed that the fluorescence maximum as well as the value of the first moment in mountain-tundra soils lies within very narrow limits and is among the lowest values identified in our studies. Humic acids of plain tundra soils differ significantly from their mountain analogues in all indicators of fluorescent properties. In conditions of vertical zonation in the direction from the zone of tundra soils to the zone of steppe mountain areas, a shift of the fluorescence maximum towards an increase in the wavelength is observed, however, it does not go beyond the boundaries of the blue region of the spectrum. The maximum values of these indicators are characteristic of the fluorescence of GC soils of steppe areas of intermountain basins and steppe areas of plain conditions of the Trans-Urals and Altai Region Territory. The assessment of the significance of humic acid differences in the fluorescence properties of soils of hillocks and sports of plain tundra showed that the values of λ and M differ by 10 and 7 units, respectively, and that the differences between them are significant. Differences for other objects formed in different natural conditions at the local level in the absolute majority of cases turned out to be significant. The existence of a close correlation of the values of quantitative indicators of the fluorescent properties of humic acids with the ratio of the main structure–forming elements - H:C and with climatic parameters is shown, using the example of mountain soils of Tuva and pedogenically processed deposits of the archaeological monument Grotto Obi-Rahmat, which allows us to recommend the use of these easily and quickly obtaining characteristics as an indicator for assessing the state of soils and the natural environment.

First-Class State Working Standard of Units of Wavelength in the Range from 1.25 to 20.00 μm and of Wavenumber in the Range from 500 to 8000 cm–1

The first-class State Working Standard of units of wavelength in the range from 1.25 to 20.00 μm and of units of wavenumber in the range from 500 to 8000 cm–1 developed at the All-Russia Research Institute of Optophysical Measurements on the basis of an infrared Fourier spectrometer is presented. The units of wavelength and units of wavenumber are transmitted to working standards in the course of a measurement (performed by an infrared Fourier spectrometer) of the positions of the radiation peaks from two laser sources incorporated into GET 170-2011, the State Primary Special Standard of the units of length and propagation time of a signal in an optical cable, mean power, attenuation, and wavelength for fiber-optic communication systems and information transmission systems. The working standard reproduces the spectral scale with the use of an interference pattern produced by a built-in He–Ne laser in the course of measurements of the spectral distribution of the strength of the internal source. Propagation of the wavelength scale in the range 1.25–20.00 μm and of the wavenumber scale in the range 500–8000 cm–1 is achieved through the introduction of corresponding correction factors to the results of measurements. An accuracy chart that establishes the traceability of an instrument used to measure wavelength and wavenumber to GET 170–2011 is developed and presented.

A new CBD-CC-E spectral similarity scale for optimizing computer-simulated UV–vis spectra

A new CBD-CC-E spectral similarity scale is proposed to optimize computer-simulated UV–vis spectra. The scale was tested using the S1←S0 spectrum of the dithienyl-diketopyrrolopyrrole molecule (DPP2T), an important building block for manufacturing materials for optoelectronic applications. Our results indicate that the spectrum calculated at M06/6-311++G(d,p) level was the one that best reproduced the intensity and shape features of the experimental spectrum, while CAM-B3LYP/6-311++G(d,p) was the one that best reproduced the energy. The CBD-CC-E scale makes the comparison between computer-simulated and experimental spectra statistically based, allowing a systematic and automated choice of the theory level whose calculated spectrum best reproduces the shape, intensity or energy of the experimental UV–vis spectrum.

Possibility of Zhuhai-1 Hyperspectral Imagery for Monitoring Salinized Soil Moisture Content Using Fractional Order Differentially Optimized Spectral Indices

The possibility of quantitative inversion of salinized soil moisture content (SMC) from Zhuhai-1 hyperspectral imagery and the application effect of fractional order differentially optimized spectral indices were discussed, which provided new research ideas for improving the accuracy of hyperspectral remote sensing inversion. The hyperspectral data from indoor and Zhuhai-1 remote sensing imagery were resampled to the same spectral scale. The soil hyperspectral data were processed by fractional order differential preprocessing method and optimized spectral indices method, and the Pearson correlation coefficient (PCC/r) analysis was made with SMC data. The sensitive optimized spectral indices were used to establish the ground hyperspectral estimation model, and a variety of modeling methods were used to select the best SMC inversion model. The results were as follows: the maximum one-dimensional r between SMC and the 466–938 nm band was −0.635, the maximum one-dimensional r with the 0.5-order absorbance spectrum was 0.665, and the maximum two-dimensional r with the difference index (DI) calculated by the 0.5-order absorbance spectrum was ±0.72. The maximum three-dimensional r with the triangle vegetation index (TVI) calculated from the 0.5-order absorbance spectrum reached 0.755, which exceeded the one-dimensional r extreme value of 400–2400 nm. The TreeNet gradient boosting machine (TGBM) regression model had the highest modeling accuracy, with a calibration coefficient of determination (R2C) = 0.887, calibration root mean square error (RMSEC) = 2.488%, standard deviation (SD) = 6.733%, and r = 0.942. However, the partial least squares regression (PLSR) model had the strongest predictive ability, with validation coefficient of determination (R2V) = 0.787, validation root mean square error (RMSEV) = 3.247%, and relative prediction deviation (RPD) = 2.071. The variable importance in projection (VIP) method could not only improve model efficiency but also increased model accuracy. R2C of the optimal PLSR model was 0.733, RMSEC was 3.028%, R2V was 0.805, RMSEV was 3.100%, RPD was 1.976, and Akaike information criterion (AIC) was 151.050. The three-band optimized spectral indices with fractional differential pretreatment could to a certain extent break through the limitation of visible near-infrared spectrum in SMC estimation due to the lack of shortwave infrared spectra, which made it possible to quantitatively retrieve saline SMC on the basis of Zhuhai-1 hyperspectral imagery.

Universality of local spectral statistics of products of random matrices

We derive exact analytical expressions for correlation functions of singular values of the product of M Ginibre matrices of size N in the double scaling limit M,N→∞. The singular value statistics is described by a determinantal point process with a kernel that interpolates between Gaussian unitary ensemble statistic and Dirac-delta (picket-fence) statistic. In the thermodynamic limit N→∞, the interpolation parameter is given by the limiting quotient a=N/M. One of our goals is to find an explicit form of the kernel at the hard edge, in the bulk, and at the soft edge for any a. We find that in addition to the standard scaling regimes, there is a transitional regime which interpolates between the hard edge and the bulk. We conjecture that these results are universal, and that they apply to a broad class of products of random matrices from the Gaussian basin of attraction, including correlated matrices. We corroborate this conjecture by numerical simulations. Additionally, we show that the local spectral statistics of the considered random matrix products is identical with the local statistics of Dyson Brownian motion with the initial condition given by equidistant positions, with the crucial difference that this equivalence holds only locally. Finally, we have identified a mesoscopic spectral scale at the soft edge which is crucial for the unfolding of the spectrum.

Establishment of 2π total spectral radiant flux scale with a broadband LED-based transfer standard source

The National Metrology Institute of Japan realized a total spectral radiant flux scale in the visible wavelength range (from 380 nm to 780 nm) for sphere-spectroradiometer calibration in 2π geometry. For a transfer standard in 2π geometry, a standard source based on a specially-designed broadband light-emitting diode (2π standard LED) was used. For the scale realization, we used the goniophotometer/spectroradiometer system. In the realization, an effect of a bandpass function of the array spectroradiometer was corrected by a matrix inversion approach. The relative expanded uncertainty (k = 2) for the scale is from 3.3% to 5.7% depending on the wavelength range. We also evaluated the contributions of the wavelength calibration and the bandpass function to the measurement of the total spectral radiant flux of typical white LEDs against the 2π standard LED. Our results demonstrate that the 2π standard LED achieves uncertainties comparable to those of a conventional standard lamp, within a practical wavelength range for LED measurements. These results show that the 2π standard LED is a useful transfer standard for the realization of the total spectral radiant flux scale and for evaluation of the total luminous flux of LEDs in 2π geometry.

Spectral irradiance primary scale realization and characterization of deuterium lamps from 200 to 400 nm.

To meet the increasing metrology demand of spectral irradiance in the short UV spectral range, a new spectral irradiance scale from 200 to 400 nm was realized at National Institute of Metrology (NIM) based on a high-temperature blackbody BB3500M, and a group of stable deuterium lamps are used as the transfer standards. Accurate real-time temperature of a blackbody is derived to reduce the temperature drift during the measurement period. A combination of an absolute and relative measurement system is designed to reduce repeatability uncertainty, and a selective optical filter method is used to remove fluorescence with a peak at 330 nm. A seven-point bandwidth novel correction method based on differential quadrature formula is put forward to correct the bandwidth error of the monochromator. The expanded uncertainties of the new spectral irradiance scale are 5.3% at 200 nm, 1.8% at 250 nm, 1.9% at 330 nm, and 3.6% at 400 nm, respectively. In the overlap wavelength from 250 to 400 nm, the average deviation between two types transfer standards, deuterium lamps and tungsten halogen lamps, is verified to be 0.39%, which are consistent with the associated measurement uncertainties.

Forest and Crop Leaf Area Index Estimation Using Remote Sensing: Research Trends and Future Directions

Leaf area index (LAI) is an important vegetation leaf structure parameter in forest and agricultural ecosystems. Remote sensing techniques can provide an effective alternative to field-based observation of LAI. Differences in canopy structure result in different sensor types (active or passive), platforms (terrestrial, airborne, or satellite), and models being appropriate for the LAI estimation of forest and agricultural systems. This study reviews the application of remote sensing-based approaches across different system configurations (passive, active, and multisource sensors on different collection platforms) that are used to estimate forest and crop LAI and explores uncertainty analysis in LAI estimation. A comparison of the difference in LAI estimation for forest and agricultural applications given the different structure of these ecosystems is presented, particularly as this relates to spatial scale. The ease of use of empirical models supports these as the preferred choice for forest and crop LAI estimation. However, performance variation among different empirical models for forest and crop LAI estimation limits the broad application of specific models. The development of models that facilitate the strategic incorporation of local physiology and biochemistry parameters for specific forests and crop growth stages from various temperature zones could improve the accuracy of LAI estimation models and help develop models that can be applied more broadly. In terms of scale issues, both spectral and spatial scales impact the estimation of LAI. Exploration of the quantitative relationship between scales of data from different sensors could help forest and crop managers more appropriately and effectively apply different data sources. Uncertainty coming from various sources results in reduced accuracy in estimating LAI. While Bayesian approaches have proven effective to quantify LAI estimation uncertainty based on the uncertainty of model inputs, there is still a need to quantify uncertainty from remote sensing data source, ground measurements and related environmental factors to mitigate the impacts of model uncertainty and improve LAI estimation.

Spectral Calibration Algorithm for the Geostationary Environment Monitoring Spectrometer (GEMS)

The Geostationary Environment Monitoring Spectrometer (GEMS) onboard the Geostationary Korean Multi-Purpose Satellite 2B was successfully launched in February 2020. GEMS is a hyperspectral spectrometer measuring solar irradiance and Earth radiance in the wavelength range of 300 to 500 nm. This paper introduces the spectral calibration algorithm for GEMS, which uses a nonlinear least-squares approach. Sensitivity tests for a series of unknown algorithm parameters such as spectral range for fitting, spectral response function (SRF), and reference spectrum were conducted using the synthetic GEMS spectrum prepared with the ground-measured GEMS SRF. The test results show that the required accuracy of 0.002 nm is achievable provided the SRF and the high-resolution reference spectrum are properly prepared. Such a satisfactory performance is possible mainly due to the inclusion of additional fitting parameters of spectral scales (shift, squeeze, and high order shifts) and SRF (width, shape and asymmetry). For the application to the actual GEMS data, in-orbit SRF is to be monitored using an analytic SRF function and the measured GEMS solar irradiance, while a reference spectrum is going to be selected during the instrument in-orbit test. The calibrated GEMS data is expected to be released by the end of 2020.