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.

Quantum and classical studies of the O(3P)+H2(v=0–3,j=0)→OH+H reaction using benchmark potential surfaces

Abstract: We present results of time-dependent quantum mechanics (TDQM) and quasiclassical trajectory (QCT) studies of the excitation function for O(3P)+H2(v=0–3,j=0)→OH+H from threshold to 30 kcal/mol collision energy using benchmark potential energy surfaces [Rogers et al., J. Phys. Chem. A 104, 2308 (2000)]. For H2(v=0) there is excellent agreement between quantum and classical results. The TDQM results show that the reactive threshold drops from 10 kcal/mol for v=0 to 6 for v=1, 5 for v=2 and 4 for v=3, suggesting a much slower increase in rate constant with vibrational excitation above v=1 than below. For H2(v>0), the classical results are larger than the quantum results by a factor ∼2 near threshold, but the agreement monotonically improves until they are within ∼10% near 30 kcal/mol collision energy. We believe these differences arise from stronger vibrational adiabaticity in the quantum dynamics, an effect examined before for this system at lower energies. We have also computed QCT OH(v′,j′) state-resolved ...

Laser Raman sensor for measurement of trace-hydrogen gas

Abstract: A new optical hydrogen sensor based on spontaneous Raman scattering of laser light has been designed and constructed for rugged field use. It provides good sensitivity, rapid response, and the inherent Raman characteristics of linearity and background gas independence of the signal. Efficient light collection and discrimination by using fast optics and a bandpass interference filter compensate for the inefficiency of the Raman-scattering process. A multipass optical cavity with a Herriott-type configuration provides intense illumination from an air-cooled CW gas laser. The observed performance is in good agreement with the theoretical signal and noise level predictions.

Space telescope and optical reverberation mapping project. VII. Understanding the ultraviolet anomaly in NGC 5548 with x-ray spectroscopy.

Abstract: During the Space Telescope and Optical Reverberation Mapping Project observations of NGC 5548, the continuum and emission-line variability became decorrelated during the second half of the six-month-long observing campaign. Here we present Swift and Chandra X-ray spectra of NGC 5548 obtained as part of the campaign. The Swift spectra show that excess flux (relative to a power-law continuum) in the soft X-ray band appears before the start of the anomalous emission-line behavior, peaks during the period of the anomaly, and then declines. This is a model-independent result suggesting that the soft excess is related to the anomaly. We divide the Swift data into on- and off-anomaly spectra to characterize the soft excess via spectral fitting. The cause of the spectral differences is likely due to a change in the intrinsic spectrum rather than to variable obscuration or partial covering. The Chandra spectra have lower signal-to-noise ratios, but are consistent with the Swift data. Our preferred model of the soft excess is emission from an optically thick, warm Comptonizing corona, the effective optical depth of which increases during the anomaly. This model simultaneously explains all three observations: the UV emission-line flux decrease, the soft-excess increase, and the emission-line anomaly.

Space Telescope and Optical Reverberation Mapping Project. VIII. Time Variability of Emission and Absorption in NGC 5548 Based on Modeling the Ultraviolet Spectrum

Abstract: We model the ultraviolet spectra of the Seyfert 1 galaxy NGC 5548 obtained with the Hubble Space Telescope during the 6 month reverberation mapping campaign in 2014. Our model of the emission from NGC 5548 corrects for overlying absorption and deblends the individual emission lines. Using the modeled spectra, we measure the response to continuum variations for the deblended and absorption-corrected individual broad emission lines, the velocity-dependent profiles of Lyα and C iv, and the narrow and broad intrinsic absorption features. We find that the time lags for the corrected emission lines are comparable to those for the original data. The velocity-binned lag profiles of Lyα and C iv have a double-peaked structure indicative of a truncated Keplerian disk. The narrow absorption lines show a delayed response to continuum variations corresponding to recombination in gas with a density of ~105 cm−3. The high-ionization narrow absorption lines decorrelate from continuum variations during the same period as the broad emission lines. Analyzing the response of these absorption lines during this period shows that the ionizing flux is diminished in strength relative to the far-ultraviolet continuum. The broad absorption lines associated with the X-ray obscurer decrease in strength during this same time interval. The appearance of X-ray obscuration in ~2012 corresponds with an increase in the luminosity of NGC 5548 following an extended low state. We suggest that the obscurer is a disk wind triggered by the brightening of NGC 5548 following the decrease in size of the broad-line region during the preceding low-luminosity state.

FLAASH and MODTRAN4: state-of-the-art atmospheric correction for hyperspectral data

Abstract: FLAASH (Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes) is a MODTRAN-based "atmospheric correction" software package which is being developed by the Air Force Research Laboratory, Hanscom AFB, and Spectral Sciences, Inc., to support current and planned SWIR/visible/UV hyperspectral and multispectral sensors, typically in image format. The AF intent is to provide surface reflectance and emissivity image cubes of sufficient accuracy for input into subsequent analyses of surface properties, effectively removing the atmospheric component. The main objectives are (1) accurate, physics-based descriptions of surface and atmospheric properties (such as surface albedo, relative elevation, water vapor column, aerosol and cloud optical properties, and temperatures), (2) minimal computational time requirements, and (3) interactive, user-friendly interface for generating MODTRAN4-based look-up tables. Validation and development exercises are being carried out on data from the airborne AVIRTS and HYDICE sensors, which cover the 0.4-2.5 /spl mu/m region; applications are also planned for infrared sensors. The algorithms for deriving the surface and atmospheric properties utilize the full MODTRAN4 accuracy (thermal and solar) and account for adjacency effects associated with atmospheric scattering. A new line-tail treatment and a correlated-k (CK) radiative transfer algorithm provide improved accuracy, especially under conditions of partial cloud cover and/or heavy aerosol loading.