Software for Remote Sensing and Gas-Phase Spectroscopy:
MODTRAN - SHARC - SAMM - FLAMES - UVRAD - FLAASH
SSI has developed a number of first-principle computer models for radiation propagated through or generated by the atmosphere and by high-temperature and non-equilibrium gases. This software includes standard codes such as MODTRAN which are widely used by Government and industrial researchers and analysts. Applications include predicting atmospheric backgrounds, calculating atmospheric transmission for remote sensing, and simulating the optical properties of exhaust plumes and high-temperature process flows. Examples include:
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MODTRAN (MODerate resolution TRANsmission model) The DoD standard atmospheric infrared/visible/ultraviolet radiance and transmission band model for lower altitudes, developed and maintained by SSI and the US Air Force Research Laboratory (Berk et al., 1999; Acharya et al., 1999). MODTRAN rapidly predicts the atmospheric emission, thermal scatter, and solar scatter for arbitrary, refracted paths above the curved earth, incorporating the effects of molecular absorbers and scatterers, aerosols and clouds. MODTRAN's 2-cm-1 spectral resolution radiances and vertical fluxes have been extensively validated over its full spectral range from 1 to 50,000 cm-1 (0.2 - 10,000 um).
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Atmospheric heating and
cooling calculated with MODTRAN
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SHARC (Strategic High-Altitude Radiation Code) was developed by SSI for the USAF as a non-equilibrium high-altitude (up to 300 km) infrared emission model for quiescent and aurorally disturbed atmospheres. The SHARC 3-D atmosphere model solves the chemical kinetic equations pertinent above 30 km altitude to determine non-equilibrium distributions of molecular vibrational states, which are incorporated into line-of-sight calculations to determine path radiances and transmittances from 30 to 300 km. SHARC has been validated against measurements, and includes the effects of atmospheric structure, auroral enhancements, and solar terminator physics.
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SAMM and A3RTSS The SAMM (SHARC And MODTRAN Merged) code provides a seamless integration of the SHARC and MODTRAN atmospheric radiation transport algorithms, extending the modeling capabilities down to ground level. The more recent SAMM2 code provides a unified capability in which a single kinetic and radiation transport algorithm operates under both thermal equilibrium and non-equilibrium conditions. The new A3RTSS (All Altitude Atmospheric Radiation Transport for Scene Simulation) code is a completely restructured and modernized version of SAMM2 that incorporates new radiation transport algorithms of varying degrees of fidelity, increased efficiency for multiple line-of-sight scene computations, and the ability to readily integrate additional physical models.
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FLAMES (Fast Line-of-sight Algorithm for Molecular Emission Spectra) - Computes equilibrium and non-equilibrium molecular emission and transmission from high-temperature gases like those in combustion flows. It treats inhomogeneous lines of sight, has a user-specified resolution (typically 1 cm-1 or lower), handles a broad temperature range (10-5,000 K), applies throughout the pressure- to Doppler-broadened linewidth regime, covers a broad wavelength region (2-20 microns), and includes a variety of molecular species (H2O, CO2, CO, HCl, HF, OH, NO).
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UVRAD (Ultraviolet and Visible RADiation) - Computes equilibrium and non-equilibrium (e.g., chemiluminescent) diatomic UV/visible emission and transmission from high-temperature gases like those in flames. It treats inhomogeneous lines of sight, has a user-specified spectral resolution (typically 1 cm-1 or lower), handles a broad temperature range (10-10,000 K), applies throughout the pressure- to Doppler-broadened linewidth regime, and currently supports CO, OH, C2, CH, NH, NO, and CN band systems.
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FLAASH (Atmospheric Correction Of Hyperspectral/Multispectral Imagery) Spectral imagery of the Earth's surface from airborne or space platforms can be used to fullest advantage only when the effects of the atmosphere (e.g., from aerosol, water vapor, etc.) have been removed and the data are reduced to units of reflectance. In collaboration with the Air Force Research Laboratory and other US Government agencies, SSI has developed a state-of-the-art, first-principles atmospheric removal (or "correction") algorithm called FLAASH (Fast Line-of-sight Atmospheric Analysis of Spectral Hypecubes). FLAASH handles data from a variety of HSI and MSI sensors, supports off-nadir as well as nadir viewing, and incorporates algorithms for water vapor and aerosol retrieval and adjacency effect correction. (Adler-Golden et al., 1999; Matthew et al., 2000).
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FLAASH handles data from a variety of hyperspectral sensors (including AVIRIS, Hyperion, HyMap, HYDICE, CASI, and Probe-1), supports off-nadir as well as nadir viewing, and incorporates algorithms for water vapor and aerosol retrieval and adjacency effect correction. FLAASH performs its radiation transport calculations with an embedded MODTRAN4 the latest and most accurate version of the industry-standard MODTRAN atmospheric radiance and transmission model that has been developed and maintained by AFRL and Spectral Sciences. Support for multispectral sensors is currently under development.
FLAASH is now available to the remote sensing community as an add-on for ENVI, the popular and powerful image visualization and processing software by Research Systems, Inc. (RSI). To inquire about ENVI FLAASH, please visit the RSI web site at www.ittvis.com. For custom atmospheric correction implementations, please contact Dr. Steven Adler-Golden at sag(at)spectral.com.
- Image Exploitation Algorithms SSI is also active in the development of algorithms for spectral image exploitation, including target detection and classification. For example, SSI scientists developed SMACC (Sequential Maximum Angle Convex Cone), a fast, fully automated endmember-finding and unmixing algorithm that can be applied to multispectral as well as hyperspectral data. It is licensed to ITT Visual Information Systems, and is included as a spectral analysis tool in ENVI.
SMACC-derived mineral endmembers (top) and their abundances (bottom) in AVIRIS imagery of Cuprite, NE.