This paper presents an UltraViolet-Visible (UV-Vis) spectral radiance simulation capability for Non-Local Thermodynamic Equilibrium (non-LTE) conditions, consisting of a full line-by-line (LBL) radiative transfer (RT) algorithm and a UV-Vis signatures library. Results are presented for two example scenarios where strong UV-Vis emissions arise, an atmospheric high altitude auroral event and a High Explosive (HE) detonation.
Optimal interpretation of remote sensing imagery requires characterizing the atmospheric composition between a sensor and the area it is observing. Timely estimates of atmospheric temperature, water vapor, and other constituents from the ground to the edge of the space environment are not always readily available. In those cases, we must supplement our knowledge of the atmosphere’s composition to fill in any gaps in knowledge and empirical models of the atmosphere are useful tools for this purpose. The Standardized Atmosphere Generator (SAG) was constructed is one such empirical. It has been designed to allow all the major known, systematic variability in the atmosphere and may be used to generate atmospheric profile from the ground to 300 km consistent with user-specified temporal, geophysical, and geographical information Output provides reasonable estimates for temperature, pressure, and densities of atmospheric constituents and can be directly incorporated into radiative transfer forward models or retrieval algorithms. SAG draws upon a number of existing empirical atmospheric models and ensures consistency of output between them. It can be used either as a stand-alone interactive program or scripted for batch execution and assist in determining atmospheric attenuation, refraction, scattering, chemical kinetic temperature profiles, and a host of other naturally occurring processes. Here, we will discuss the capabilities and performance of the SAG model for a variety of applications including its interactive and batch processing use. We will also demonstrate the physical realism of SAG through a small number of relevant use cases.
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.
This paper presents results that demonstrate the auroral modeling capabilities of the Air Force Research Laboratory
(AFRL) SAMM2 (SHARC And MODTRAN® Merged 2) radiance code. A scene generation capability is obtained by
coupling SAMM2 with a recently developed Clutter Region Atmosphere and Scene Module (CRASMO), which
provides an approach for rapid generation of time sequences and images of radiance clutter. Modeled results will be
compared to data collected by the Midcourse Space Experiment (MSX)1 in the IR and UV-visible spectral regions during
an auroral event on November 10, 1996.
The paper is organized as follows. We first present a brief history of the AFRL SHARC/SAMM codes, leading up to the
current version, SAMM2 v.2. The SAMM2 UV-visible auroral kinetic model will then be described, followed by a
comparison of modeled results to the MSX data.
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 kURT-MS, where kURT stands for correlated-k-based Ultra-fast Radiative Transfer. The MLOS
capability is based on DISORT and exploits the existing MODTRAN-DISORT interface. kURT-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: kURT-MS and MODTRAN-kURT) 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.
A new correlated-k algorithm has recently been incorporated into SAMM-2, the Air Force Research Laboratory
background radiance and transmission code. SAMM-2 incorporates all of the major components necessary for
background scene generation at all altitudes: atmospheric characterization, solar irradiance, molecular chemical kinetics
and molecular spectroscopic data. The underlying physical models are applicable for both low-altitude local
thermodynamic equilibrium (LTE) conditions as well as high-altitude non-LTE (NLTE) conditions. Comprehensive
coverage in the .4 to 40 micron (250 to 25,000 wavenumber) wavelength region for arbitrary lines-of-sight (LOS) in the
0 to 300 kilometer altitude regime is provided. A novel 1 cm-1 resolution correlated-k algorithm has been developed in
order to provide the orders-of-magnitude increase in computational efficiency when compared to the existing SAMM-2
line-by-line (LBL) algorithm and applicable to both LTE and NLTE atmospheric conditions. The SAMM-2 correlated-k
algorithm processes molecular lines at runtime by reading line center information from the HITRAN 2000 database and
computing statistical cumulative probability distributions within a spectral interval under the presumption of a Voigt line
shape profile. This algorithm is useful for treating atmospheric phenomena at all altitudes requiring a spectrally
monochromatic treatment of the atmospheric transmission and/or radiance, including multiple scattering or atmospheric structure.
The ability to rapidly calculate at-sensor radiance over a large number of lines of sight (LOSs) is critical for scene
simulations, which are increasingly used for sensor design, performance evaluation, and data analysis. We have recently
demonstrated a new radiation transport (RT) capability that combines an efficient multiple-LOS multiple scattering
algorithm with a broad-bandpass correlated-k methodology called kURT-MS. The multiple-LOS capability is based on
DISORT and exploits the existing MODTRAN-DISORT interface. kURT-MS is a new sensor-specific correlated-k (c-k)
ultra-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 compact k-dependent source
terms and used in the 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 has potential applications for hyperspectral scene simulations as well as target acquisition algorithms for
near earth scenarios.
A new sensor-specific correlated-k (c-k) ultra-fast radiative transfer (RT) formalism, kURT, has been designed for fast broad-bandpass scene simulations from UV-visible to LWIR wavelengths. A higher resolution RT code (1 cm-1 MODTRAN) has been adapted to output 1 cm-1 correlated-k parameters for ozone, water, and the combined uniformly mixed species on a pressure-temperature grid, which are merged to form a compact c-k set incorporating the sensor bandpass response function. The compact set is used to compute bandpass transmittance and radiance in near-real time. Scattering parameters (molecular Rayleigh, clouds and aerosols), blackbody and solar functions are cast as compact k-dependent source terms and used in the radiance computations. Preliminary transmittance results for 3-5 and 8-12 micron bandpasses and visible-MWIR sensors yield results within 2% of a 1 cm-1 MODTRAN calculation with a two-orders-of-magnitude computational savings. Applications include near-earth broadband propagation and extinction calculations for target detection and recognition, mid-range tracking, and search and rescue operations from ground and low altitude aircraft.
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