Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Summary of reduced order gas cloud model, with sink terms set to zero. (a) Cloud is an oblate spheroid with uniform temperature and concentrations. The cloud model is augmented with an atmosphere model that gives pressure, temperature, and wind velocity. (b) The governing equations are first order ordinary differential equations for mass, velocity, position, and enthalpy and enforce conservation of mass, momentum, and energy. (c) The dependent variables in the governing equations are linked to the shape, size, and cloud composition through auxiliary conditions, which include the ideal gas equation of state, ideal gas property relationship for enthalpy, accounting for the changing cloud composition and the shape definition and constraint to prevent ground penetration. Solution of the model is easily accomplished through numerical integration in time domain using, for instance, standard Runge-Kutta methods. 12 Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE

Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Gas cloud evolution with clouds shown every 60 sec over a 10-min period. Initial cloud radius is 10 m. The three examples are for three different atmosphere types for which simulations were run: bottom is International Standard Atmosphere (greatest cloud rise, least deformation), middle is an isothermal atmosphere, and in the top there is a temperature inversion at 100 m (least rise, greatest deformation). Cloud darkness is an indication of concentration. Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE

Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Geometry used for numerical integration. At each step, the area of overlap between the gas cloud and the rectangular element of the plane normal to the direction of integration and within the solid angle viewed by the sensor element, Ac, is found. Incident radiation is evaluated at the centroid of this overlap area, xc. Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE

Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Superimposed sequence of images obtained using the gas cloud and atmosphere parameters used for the top row of Fig. 2. The background irradiation is zero, the sky and ground irradiations are 604 and 750 μFlicks, respectively, which correspond to blackbody irradiation at the wavelength chosen (8.54 μm) and 10 deg below the ambient temperature at ground level, and blackbody irradiation at the wavelength chosen and at the ambient temperature at ground level, respectively. Finally, the mass absorptivity was uniform across all wavelengths, and the images shown are indistinguishable from images at other wavelengths. Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE

Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Comparison of simulation with field test for single instance two seconds after explosive release of a simulant (multiple clouds). The plot on the left shows the mean change of intensity from before to after the explosion at each pixel for which the ACE criterion determined target present. The triangles are the results from the simulation, while the circles depict the field test results (these are the same results shown in Fig. 6). The simulation seems to systemically produce a greater decrease in intensity. The reason for this is the need to balance matching the spectral shape with obtaining agreement between field test and simulation for other criteria, primarily column densities and DACE values, which are shown at the pixel level on the right side of the figure. Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE

Date of download: 7/10/2016 Copyright © 2016 SPIE. All rights reserved. Images are spectrally averaged irradiances with detections of a simulant superposed in white. The top row images (a), (b), and (c) are simulation results immediately following the detonation, 300 sec later, and 600 sec, respectively, while the bottom row images are the corresponding field test acquisitions. The simulant release used 12 simultaneous detonations arranged in a rectangular array. Figure Legend: From: Physics-based, reduced-order gas cloud with radiative transport model for rapid simulation of hyperspectral infrared sensors Opt. Eng. 2012;51(5): doi: /1.OE