An object oriented simulation framework, called KARMA, was developed over the last decade at Defence Research and
Development Canada - Valcartier (DRDC Valcartier) to study infrared countermeasures (IRCM) methods and tactics. It
provides a range of infrared (IR) guided weapon engagement services from constructive to HWIL simulations. To
support the increasing level of detail of its seeker models, DRDC Valcartier recently developed an IR scene generation
(IRSG) capacity for the KARMA framework. The approach relies on Open-Source based rendering of scenes composed
of 3D models, using commercial off-the-shelf (COTS) graphics processing units (GPU) of standard PCs. The objective
is to produce a high frame rate and medium fidelity representation of the IR scene, allowing to properly reproduce the
spectral, spatial, and temporal characteristics of the aircraft's and flare's signature. In particular, the OpenSceneGraph
library is used to manage the 3D models, and to send high-level rendering commands. The atmospheric module allows
for accurate, run-time computation of the radiative components using a spectrally correlated wide-band mode. Advanced
effects, such as surface reflections and zoom anti-aliasing, are computed by the GPU through the use of shaders. Also, in
addition to the IR scene generation module, a signature modeling and analysis tool (SMAT) was developed to assist the
modeler in building and validating signature models that are independent of a particular sensor type. Details of the IR
scene generation module and the associated modeling tool will be presented.
A new C++ library for radiative transfer calculations in the visible and infrared bands which uses MODTRAN as a
primary source for atmospheric optical parameters has been developed at Defense R&D Canada, Valcartier (DRDC
Valcartier). The main benefit of the library is its capability to perform fast wide spectral band calculations with an
appreciably high accuracy. Coherent calculations on wide bands are made possible by using a modified version of the
correlated-k theory. The main features of the library are discussed, and comparisons with conventional spectral
MODTRAN 4 calculations are presented. It is shown that the library is capable of producing band results that are usually
within 5% of MODTRAN 4 with computation times that are thousands of times faster.
To date, physically accurate and reasonably fast background generation in a marine environment has been an elusive objective. The pursuit has been plagued by slow radiative transfer codes and sea BRDF (bidirectional reflectance distribution functions) implementations that traded accuracy for speed. Recent developments in both these fields have put this goal into our grasp. In this paper, we show that an accurate and fast sea BRDF model can be implemented into modern radiative transfer codes. In this instance, it is integrated in a widely used code, MODTRAN 4, to produce marine environment backgrounds with an acceptable computation time and less tradeoff in accuracy.
An attempt is made to evaluate three different models correlating sea slope variance with wind speed, which are a crucial component of the statistical approach to calculating the sea surface BRDF (Bidirectional Reflectance Distribution Function). The models are those of Cox & Munk, Wu and Mermelstein et al. This is done with the help of publicly available upwelling radiance data taken at the COVE rigid costal platform with a scanning spectral photometer at wavelengths around 444 nm, 501 nm, 677 nm and 864 nm for a wide range of azimuth and elevation angles. The three sea slop variance models are compared with variances inferred from the data by inverting a BRDF models that includes facet hiding and shadowing as well as facet projection weighing. The validity of the models is discussed in the context of varying wind speed and direction. Limitations when dealing with near-horizon BRDF modeling using these statistical models are discussed along with potential improvements.
Near the sea surface, strong gradients of temperature and moisture affect the path taken by propagating radiation. Strong gradients in aerosol properties may also be present causing transmittance and radiance to be strongly dependent on the exact path taken by radiation, especially when viewing angles are nearly horizontal. So far, the rapid changes of atmospheric properties with altitude near the surface have been neglected in the calculations of transmittance and path radiance. In this paper, calculations of transmittances under sub- and super-refraction conditions are presented. It is shown that transmittance can vary significantly when accounting for refraction in platform based or limb viewing conditions. Furthermore, calculations of path-radiance in the surface layer, which accounts for the scattering of incident radiation, will be addressed and computational results presented.
An imaging polarimeter for the visible has been built for the mont Megantic Observatory. It uses a new design with a Foster prism which allows to obtain the two orthogonal beams of polarized light onto the detector at the same time, thus alleviating calibration problems associated with variations in the sky transparency during the observations. The field of view is 2.4 arc minutes at the f/15 focus of the telescope. A rotating achromatic half-wave plate is used to get all the linear polarization components and eliminate systematic calibration effects. Circularly polarized images can also be obtained by substituting a quarter-wave plate for the rotating half-wave plate. A user-friendly software for carrying out the data reduction has been developed.