Spectral Sciences Incorporated

About: Spectral Sciences Incorporated is a company organization based out in Burlington, Massachusetts, United States. It is known for research contribution in the topics: Hyperspectral imaging & Radiance. The organization has 114 authors who have published 342 publications receiving 10875 citations.

Very Narrow Band Model Calculations of Atmospheric Fluxes and Cooling Rates

Abstract: A new very narrow band model (VNBM) approach has been developed and incorporated into the MODTRAN atmospheric transmittance–radiance code. The VNBM includes a computational spectral resolution of 1 cm−1, a single-line Voigt equivalent width formalism that is based on the Rodgers–Williams approximation and accounts for the finite spectral width of the interval, explicit consideration of line tails, a statistical line overlap correction, a new sublayer integration approach that treats the effect of the sublayer temperature gradient on the path radiance, and the Curtis–Godson (CG) approximation for inhomogeneous paths. A modified procedure for determining the line density parameter 1/d is introduced, which reduces its magnitude. This results in a partial correction of the VNBM tendency to overestimate the interval equivalent widths. The standard two parameter CG approximation is used for H2O and CO2, while the Goody three parameter CG approximation is used for O3. Atmospheric flux and cooling rate p...

Supermassive black holes with high accretion rates in active galactic nuclei. XI. Accretion disk reverberation mapping of Mrk 142

Abstract: We performed an intensive accretion disk reverberation mapping campaign on the high accretion rate active galactic nucleus Mrk 142 in early 2019. Mrk 142 was monitored with the Neil Gehrels Swift Observatoryfor4 months in X-rays and 6 UV/optical filters. Ground-based photometric monitoring was obtained from the Las Cumbres Observatory, Liverpool Telescope and Dan Zowada Memorial Observatory in ugriz filters and the Yunnan Astronomical Observatory in V. Mrk 142 was highly variable throughout, displaying correlated variability across all wavelengths. We measure significant time lags between the different wavelength light curves, finding that through the UV and optical the wavelength-dependent lags, τ(λ), generally follow the relation τ(λ)∝λ4/3, as expected for theT∝R−3/4profile of a steady-state optically-thick, geometrically-thin accretion disk, though can also be fit by τ(λ)∝λ2, as expected for a slim disk. The exceptions are the u and U band, where an excess lag is observed, as has been observed in other AGN and attributed to continuum emission arising in the broad-line region. Furthermore, we perform a flux-flux analysis to separate the constant and variable components of the spectral energy distribution, finding that the flux-dependence of the variable component is consistent with thefν∝ν1/3spectrum expected for a geometrically-thin accretion disk. Moreover, the X-ray to UV lag is significantly offset from an extrapolation of the UV/optical trend, with the X-rays showing a poorer correlation with the UV than the UV does with the optical. The magnitude of the UV/optical lags is consistent with a highly super-Eddington accretion rate.

Near-infrared collisional radiative model for Xe plasma electrostatic thrusters: the role of metastable atoms

Abstract: Mestastable Xe atoms play an important role in the collisional radiative processes of dense xenon plasmas, including those of electric thrusters for space vehicles. Recent measurements and calculations of electron-excitation processes out of the 5p56s J = 2 metastable state (1s5 state in Paschen notation) have allowed for the development of a collisional radiative model for Xe near-infrared (NIR) emissions based on the population of the metastable level through 2p?1s5 radiative transitions, and based on depopulation through electron-impact excitation. A modified plasma radiative model incorporating newly computed electron-impact excitation cross sections using both relativistic distorted wave and semi-relativistic Breit?Pauli B-Spline R-matrix methods is presented. The model applies to optically thin, low-density regions of the thruster plasma and is most accurate at electron temperatures below 10?eV. The model is tested on laboratory spectral measurements of the D55 TAL and BHT-200 Hall thruster plasma NIR radiation. The metastable neutral fraction is determined to rise from 0.1 to slightly above 1% as the electron temperature increases from ~2 to 10?eV, reaching a maximum around 15?eV. Electron temperatures derived with the modified model are approximately 20% lower than a previous version of the model that used an approximate approach to account for metastable population and line intensity enhancement.

System and method for remote detection and identification of chemical species by laser initiated nonresonant infrared spectroscopy

Abstract: Disclosed is a system and method for remote detection and identification of unknown chemical species in gaseous, aerosol, and liquid states. A pulsed infrared laser is directed at an unknown chemical mass which absorbs energy at the laser wavelength. Due to molecular energy transfer processes, the absorbed laser energy can be re-emitted in one or more wavelength regions nonresonant with the laser wavelength. The re-emitted energy is detected for a period of time which is comparable to or less than the characteristic time for the absorbed radiative energy to be dissipated as heat. The nonresonant infrared emission spectrum of the unknown chemical species is detected with several infrared detectors. The identity of the unknown species, as well as its range and concentration, may be established by comparison of its spectrum to that for known species.

Systems and methods for optically measuring properties of hydrocarbon fuel gases

Abstract: A system and method for optical interrogation and measurement of hydrocarbon fuel gas includes a light source (24) generating light at near-visible wavelengths. A cell (30) containing the gas is optically coupled to the light source which is in turn partially transmitted by the sample. A spectrometer (26) disperses the transmitted light and captures an image thereof. The image is captured by a low-cost silicon-based two-dimensional CCD array (46). The captured spectral image is processed by electronics for determining energy or BTU content and composition of the gas. The innovative optical approach provides a relatively inexpensive, durable, maintenance-free sensor and method which is reliable in the field and relatively simple to calibrate. In view of the above, accurate monitoring is possible at a plurality of locations along the distribution chain leading to more efficient distribution.