Coherent Combination Propagation Method
Full scalar wave propagation (spectral) using the Angular Spectrum Method.
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Results for “spectral methods”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Determination of electron temperature in a Penning discharge by the helium line ratio method
The helium spectral line intensity ratio technique utilizes the difference in electron energy dependences of the ground state electron impact excitation cross sections of the singlet and triplet series of neutral helium and the excited states of helium ions to determine the electron temperatures in a toroidal steady-state Penning discharge operating in helium. By varying the Penning discharge anode voltage and background pressure over a range of 2.5 to 28 kV and 0.00005 to 0.0001 torr, respectively, it was possible to make a comparison of the electron temperature as measured from various possible line ratios over a wide range of temperatures (10 to 100+ eV) under reproducible steady-state conditions.
Richardson, R. W.↗
Automatic color map digitization by spectral classification
A method of converting polygon map information into a digital form which does not require manual tracing of polygon edges is discussed. The maps must be in color-coded format with a unique color for each category in the map. Color scanning using a microdensitometer is employed and a three-channel color separation digital data set is generated. The digital data are then classified by using a Gaussian maximum likelihood classifier, and the resulting digitized map is evaluated. Very good agreement is observed between the classified and original map.
Chu, N. Y.↗
The inference of vector magnetic fields from polarization measurements with limited spectral resolution
A method is presented for recovery of the vector magnetic field and thermodynamic parameters from polarization measurement of photospheric line profiles measured with filtergraphs. The method includes magneto-optic effects and may be utilized on data sampled at arbitrary wavelengths within the line profile. The accuracy of this method is explored through inversion of synthetic Stokes profiles subjected to varying levels of random noise, instrumental wave-length resolution, and line profile sampling. The level of error introduced by the systematic effect of profile sampling over a finite fraction of the 5 minute oscillation cycle is also investigated. The results presented here are intended to guide instrumental design and observational procedure.
Lites, B. W.↗
Growth and characteristics of materials for tunable lasers in the near infrared spectral region
A method for growing crystals of LiYF4 using an HF pretreatment and purification system is described. In addition, spectrum analyses were performed on eight crystals of type LiNbO3:Mg,Cr,RE, which were grown in order to investigate the use of lithium niobate as a laser host material.
Powell, Richard C.↗
Detecting strain in birefringent materials using spectral polarimetry
A method, computer program product and system for analyzing multispectral images from a plurality of regions of birefringent material, such as a polymer film, using polarized light and a corresponding polar analyzer to identify differential strain in the birefringent material. For example, the birefringement material may be low-density polyethylene (LDPE), high-density polyethylene (HDPE), polypropylene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyvinylidene chloride, polyester, nylon, or cellophane film. Optionally, the method includes generating a real-time quantitative strain map.
Ragucci, Anthony J.↗
Accuracy Of The Correlated-k Method
Report discusses accuracy of correlated-k method of calculating spectral radiances of vertically nonhomogeneous atmospheres. Presents brief description of method. Discusses some theoretical considerations, showing method correct when applied to weak spectral lines, strong pressure-broadened spectral lines, spectral lines affected by Doppler shifts at constant temperatures, and overlapping spectral bands.
Goody, Richard↗
When Spectral Modeling Meets Convolutional Networks: A Method for Discovering Reionization-era Lensed Quasars in Multiband Imaging Data
Over the last two decades, around 300 quasars have been discovered at z ≳ 6, yet only one has been identified as being strongly gravitationally lensed. We explore a new approach—enlarging the permitted spectral parameter space, while introducing a new spatial geometry veto criterion—which is implemented via image-based deep learning. We first apply this approach to a systematic search for reionization-era lensed quasars, using data from the Dark Energy Survey, the Visible and Infrared Survey Telescope for Astronomy Hemisphere Survey, and the Wide-field Infrared Survey Explorer. Our search method consists of two main parts: (i) the preselection of the candidates, based on their spectral energy distributions (SEDs), using catalog-level photometry; and (ii) relative probability calculations of the candidates being a lens or some contaminant, utilizing a convolutional neural network (CNN) classification. The training data sets are constructed by painting deflected point-source lights over actual galaxy images, to generate realistic galaxy–quasar lens models, optimized to find systems with small image separations, i.e., Einstein radii of θ E ≤ 1''. Visual inspection is then performed for sources with CNN scores of P lens > 0.1, which leads us to obtain 36 newly selected lens candidates, which are awaiting spectroscopic confirmation. These findings show that automated SED modeling and deep learning pipelines, supported by modest human input, are a promising route for detecting strong lenses from large catalogs, which can overcome the veto limitations of primarily dropout-based SED selection approaches.
High-redshift galaxies↗
Alternate Inversion Paradigm for Spectroheliogram Data
Over the past five years, new methods to reconstruct spectrally pure maps of the Sun from spectroheliogram data have emerged, essentially unlocking this long-abandoned method of obtaining both spatial and spectral information over a large field of view simultaneously. The original inversion method determined the plasma’s emission measure distribution as a function of temperature at every spatial location in the field of view. To complete this inversion, a response matrix had to be created mapping the emission measure in different (temperature, space) bins to detector, requiring assumptions on the thermal and ionization equilibrium and abundance state of the plasma. We have since derived a new method of the inversion that does not require these atomic assumptions to be made. Instead, we use only the different locations of spectral lines from the same ion species and the possible ratios of those single-species spectral lines, removing the need for a priori knowledge on the state of the emitting plasma. In this presentation, we demonstrate this method using observed data from the Marshall Grazing Incidence X-ray Spectrometer (MaGIXS) and simulated data from the EUV CME and Coronal Connectivity Observatory (ECCCO) investigation.
Amy Winebarger↗
Applicability of Spectral Decomposition by Varimax-Rotated, Principal Component Analysis to the Surface Biology and Geology (SBG) VNIR Mission Concept
Cyanobacterial and Harmful Algal Blooms (CyanoHABs) are a growing concern in coastal and inland waters. But, spectral interference from multiple constituents in optically complex waters can hamper application of remote sensing using traditional image processing methods. The Kent State University (KSU) spectral decomposition method can be applied to multispectral and hyperspectral remote sensing images (e.g. HICO and the NASA Glenn HSI2) to partition and identify signals related to cyanobacteria, algae, pigment degradation products and suspended sediment in each pixel. Fundamental to the use of remote sensing data is the ability to extract independent signals from correlated hyperspectral VNIR data cubes. The Kent State University varimax-rotated, principal component analysis method (VPCA) is important to integrate into the SBG VNIR mission concept because it provides greater specificity, a software-based SNR boost relative to hardware performance, and can assist with Cal/Val, Modeling and Applications. We present examples of the hyperspectral application of the KSU VPCA method with relevance to SBG. The information extracted by VPCA can be validated spectrally or spatially with laboratory and/or in situ sensors, which capture spatial or time series of information at discrete points within remote sensing images. Comparisons show hyperspectral sensors extract more components than multispectral ones, but more independent information can be extracted from multispectral sensors by VPCA than traditional band ratio approaches. The spectral decomposition method is capable of enhancing the signal to noise ratio (SNR) of the NASA Glenn, second-generation hyperspectral imager by a factor of 7x to 20x, with a spectral reproducibility of ±3%. The spectral decomposition method, when compared against existing remote sensing monitoring methods exhibits both greater specificity and a lower detection limit. The method has been validated with multispectral images in Lake Erie to quantify the Microcystis CyanoHAB and from the Indian River Lagoon, Florida to quantify the Brown Tide resulting from A. lagunesnsis. Field operations in the Western Basin of Lake Erie were conducted using a bbe Fluoroprobe to collect vertical profiles and horizontal tows along a transect from the Toledo to the Detroit Lighthouse during coincident satellite overpasses. Extraction of pixel values from the MODIS Aqua sensor yields agreement between in situ field and lab-based measures of cyanobacterial, cryptophyte, diatoms and green algae, suspended sediment and pigment degradation products with R2>0.8.
hyperspectral↗
Higher-order dispersion compensating pulse shaper via amplitude spectral filtering and nonlinear phase accumulation
A method of pulse shaping using spectral filtering, positive chirp, and self-phase modulation to control the accumulated higher-order phase terms of the spectral phase. This pulse shaping method has particular advantage in fiber chirped pulse amplification (FCPA) systems, where there are two effects: (1) an offsetting of the fourth order phase via nonlinear phase accumulation, allowing for a higher Strehl ratio (i.e., a cleaner pulse), higher peak power pulse and (2) enabling power scaling to higher pulse energies without the increased nonlinear phase accumulation leading to pulse breakup. This technique can be used both in a passive system with no amplification to clean up an existing pulse, and in an amplifier system to enable higher performance operation (shorter pulses, cleaner pulses, higher energy pulses).
Domingue, Scott R.↗
Experimental methods for laboratory measurements of helium spectral line broadening in white dwarf photospheres
White Dwarf (WD) stars are the most common stellar remnant in the universe. WDs usually have a hydrogen or helium atmosphere, and helium WD (called DB) spectra can be used to solve outstanding problems in stellar and galactic evolution. DB origins, which are still a mystery, must be known to solve these problems. DB masses are crucial for discriminating between different proposed DB evolutionary hypotheses. Current DB mass determination methods deliver conflicting results. The spectroscopic mass determination method relies on line broadening models that have not been validated at DB atmosphere conditions. We performed helium benchmark experiments using the White Dwarf Photosphere Experiment (WDPE) platform at Sandia National Laboratories' Z-machine that aims to study He line broadening at DB conditions. Using hydrogen/helium mixture plasmas allows investigating the importance of He Stark and van der Waals broadening simultaneously. Accurate experimental data reduction methods are essential to test these line-broadening theories. In this paper, we present data calibration methods for these benchmark He line shape experiments. We give a detailed account of data processing, spectral power calibrations, and instrument broadening measurements. Uncertainties for each data calibration step are also derived. We demonstrate that our experiments meet all benchmark experiment accuracy requirements: WDPE wavelength uncertainties are <1 Å, spectral powers can be determined to within 15%, densities are accurate at the 20% level, and instrumental broadening can be measured with 20% accuracy. Fulfilling these stringent requirements enables WDPE experimental data to provide physically meaningful conclusions about line broadening at DB conditions.
79 ASTRONOMY AND ASTROPHYSICS↗
Spectral ordering techniques for incomplete LU preconditoners for CG methods
The effectiveness of an incomplete LU (ILU) factorization as a preconditioner for the conjugate gradient method can be highly dependent on the ordering of the matrix rows during its creation. Detailed justification for two heuristics commonly used in matrix ordering for anisotropic problems is given. The bandwidth reduction and weak connection following heuristics are implemented through an ordering method based on eigenvector computations. This spectral ordering is shown to be a good representation of the heuristics. Analysis and test cases in two and three dimensional diffusion problems demonstrate when ordering is important, and when an ILU decomposition will be ordering insensitive. The applicability of the heuristics is thus evaluated and placed on a more rigorous footing.
Clift, Simon S.↗
DUAL-PARTICLE DOSEMETER BASED ON ORGANIC SCINTILLATOR
Abstract Traditionally available handheld dosemeters are generally sensitive to only one type of radiation: neutrons or photons. Some dosemeters also rely on very specific attenuation correlations between response and dose, are not scalable in size and multiple dosemeters are required to characterise mixed-particle fields. The research presented here serves as a proof-of-concept for a method to simultaneously measure dose rates from neutrons and photons using a particle discriminating organic scintillation detector without the need for spectral deconvolution. The method was compared with traditional instruments and to simulation. Isotopic photon dose rates measured with this method were within 4% of simulated truth, whereas fission spectrum neutron dose rates were measured within 21%. Measurements of dose rates from both particles agree with simulated truth better than traditional instruments. This new method allows for measurement of dose equivalent from both neutrons and photons with a single instrument and no reliance on spectral deconvolution.
Miller, C. A.↗
Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model
A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on a set of shadowgraph image pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow field pressure fluctuations. Pressure measurements collected during a Booster Obsolescence Life Extension Forward Attachment Structure Trade Study Test are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated aerodynamic environment downstream of various booster forward attachment hardware geometries of the Space Launch System Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.
Shadowgraph↗
Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model
A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on shadowgraph video pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow-field pressure fluctuations. Time-varying pressure measurements collected during a Space Launch System (SLS) unsteady aerodynamic test of an advanced Block 2 booster design are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated the aerodynamic environment downstream of candidate booster forward attachment hardware geometries of the SLS Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.
Shadowgraph↗
Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model
A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on shadowgraph video pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow-field pressure fluctuations. Time-varying pressure measurements collected during a Space Launch System (SLS) unsteady aerodynamic test of an advanced Block 2 booster design are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated the aerodynamic environment downstream of candidate booster forward attachment hardware geometries of the SLS Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.
Shadowgraph↗
The power spectral density of digital modulations transmitted over nonlinear channels
This paper examines by analytical methods the power spectral densities of digital modulations (in particular, staggered and unstaggered quadrature modulations) passed through band-limited nonlinear channels. Previously observed (by computer simulation or hardware measurement) behavior of such spectra with regard to the suppression or restoration of its sidelobes after passing through the nonlinearity is verified analytically. Several examples corresponding to specific quadrature modulations and filter-nonlinearity combinations are presented as illustrations of the general results.
Divsalar, D.↗