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.

Full Spectrum Simulation of Partly Cloudy Scenes

Abstract: Spectral imagers which collect optical data from the visible to the longwave infrared (LWIR) may collect data under partly cloudy sky scenarios. To fully exploit this data, a better understanding of the influence of cloudy conditions on the collected data is required. Here we examine the influence of broken cloud fields on collected data by simulating a partly cloudy scene as observed by hyperspectral sensors which are collecting data both above and below the cloud deck. To perform these simulations, we have used the MCScene code, a high-fidelity model for full optical spectrum (UV to LWIR) image simulation. The MCScene simulation is based on a Direct Simulation Monte Carlo approach for modeling 3D atmospheric radiative transport, as well as spatially inhomogeneous surfaces including surface BRDF effects. The model includes treatment of land and ocean surfaces, 3D terrain, 3D surface objects, and effects of finite clouds with surface shadowing.

Sources of oh(a→x) emission in the space shuttle environment

Abstract: OH(A→X) emission bands have been observed in Space Shuttle engine exhaust jets using the GLO imager spectrograph located in the payload bay. Spectra were collected at a resolution of 4 A for both day and night solar illumination conditions, all at an altitude of ~390 km. A spectral analysis is presented that identifies and quantifies three OH(A) excitation mechanisms. These include: i) solar-induced fluorescence of the OH(X) in the exhaust flow, ii) solar-induced photodissociation of H2O in the exhaust at Lyman-α and shorter wavelength far-UV lines, and iii) exhaust-atmosphere interactions, most probably through the reaction O+H2O→OH(A)+OH(X). Process i) produces a very rotationally cold and spectrally narrow component due to the rapid cooling of the OH(X) in the supersonic expansion of the exhaust flow. Processes ii) produce extremely excited OH(A), not well characterized by thermal vibrational or rotational distributions. Process iii) has a substantial activation energy, 4.79 eV, and is only slightly above threshold for the ram (180o angle of attack between O and H2O) geometry, consistent with its observation for the night ram but not the night perpendicular exhaust atmospheric interaction. Through the use of a non-equilibrium spectral emission model for OH, the integrated intensity, spectral distribution, and OH(A) internal state characterization for each of the above processes was deduced. Additional confirmation of the analysis is provided through the use of a model simulation of the space experiment to predict the total integrated intensities for processes i) and ii) for which the underlying spectroscopy, absorption cross sections, and solar excitation intensities are well established. Analysis of process (ii) has established an effective value for the fluorescence excitation cross section at ram conditions (·ETO= 5.2 eV) of (1.7 ± 0.9) × 10 -2 A 2 . Evidence for bands attributed to predissociated OH(A) vibrational levels suggest that the associated reaction cross section could be significantly higher.

Infrared transform spectral imager

Abstract: A dispersive transform spectral imager named FAROS (FAst Reconfigurable Optical Sensor) has been developed for high frame rate, moderate-to-high resolution hyperspectral imaging. A programmable digital micromirror array (DMA) modulator makes it possible to adjust spectral, temporal and spatial resolution in real time to achieve optimum tradeoff for dynamic monitoring requirements. The system’s F/2.8 collection optics produces diffraction-limited images in the mid-wave infrared (MWIR) spectral region. The optical system is based on a proprietary dual-pass Offner configuration with a single spherical mirror and a confocal spherical diffraction grating. FAROS fulfills two functions simultaneously: one output produces two-dimensional polychromatic imagery at the full focal plane array (FPA) frame rate for fast object acquisition and tracking, while the other output operates in parallel and produces variable-resolution spectral images via Hadamard transform encoding to assist in object discrimination and classification. The current version of the FAROS spectral imager is a multispectral technology demonstrator that operates in the MWIR with a 320 x 256 pixel InSb FPA running at 478 frames per second resulting in time resolution of several tens of milliseconds per hypercube. The instrument has been tested by monitoring small-scale rocket engine firings in outdoor environments. The instrument has no macro-scale moving parts, and conforms to a robust, small-volume and lightweight package, suitable for integration with small surveillance vehicles. The technology is also applicable to multispectral/hyperspectral imaging applications in diverse areas such as atmospheric contamination monitoring, agriculture, process control, and biomedical imaging, and can be adapted for use in any spectral domain from the ultraviolet (UV) to the LWIR region.

Chemical detection results from ground testing of an airborne CO 2 differential absorption lidar system

Abstract: The Air Force Research Laboratory (AFRL) Active Remote Sensing Branch has developed the Laser Airborne Remote Sensing (LARS) system for long standoff range chemical detection using the differential absorption lidar (DIAL) technique. The system is based on a high-power CO 2 laser which uses either the 12 C 16 O 2 or the 13 C 16 O 2 carbon dioxide isotopes as the lasing medium, and has output energies of up to 5 J on the stronger laser transitions. The lidar system is mounted on a flight-qualified optical breadboard designed for installation in the AFRL Argus C-135E optical testbed aircraft. This paper will present chemical detection results and issues arising from ground tests of the system performed from September to December 1998. Recent advances in implementing a frequency-agile heterodyne receiver to further increase the standoff range of the DIAL system will also be presented.

Correlated-k based fast accurate bandpass radiance and transmittance calculations for hyperspectral and multispectral scenes

Abstract: The ability to rapidly calculate at-sensor radiance over a large number of lines of sight (LOSs) is critical for hyperspectral and multispectral scene simulations and look-up table generation, both of which are increasingly used for sensor design, performance evaluation, data analysis, and software and systems evaluations. We have demonstrated a new radiation transport (RT) capability that combines an efficient multiple-LOS (MLOS) multiple scattering (MS) algorithm with a broad-bandpass correlated- k methodology called k URT-MS, where k URT stands for correlated- k -based Ultra-fast Radiative Transfer. The MLOS capability is based on DISORT and exploits the existing MODTRAN-DISORT interface. k URT-MS is a new sensor-specific fast radiative transfer formalism for UV-visible to LWIR wavelengths that is derived from MODTRAN's correlated- k parameters. Scattering parameters, blackbody and solar functions are cast as a few sensor-specific and bandpass-specific k -dependent source terms for radiance computations. Preliminary transmittance results are within 2% of MODTRAN with a two-orders-of-magnitude computational savings. Preliminary radiance computations in the visible spectrum are within a few percent of MODTRAN results, but with orders of magnitude speed up over comparable MODTRAN runs. This new RT capability (embodied in two software packages: k URT-MS and MODTRAN- k URT) has potential applications for remote sensing applications such as hyperspectral scene simulation and look-up table generation for atmospheric compensation analysis as well as target acquisition algorithms for near earth scenarios.