SSI's Atmospheric Physics group develops first principles models of atmospheric radiance, emphasizing the phenomenology at high altitudes important in missile defense applications, including target illumination, identification, and tracking.
Both non-equilibrium (NLTE) and equilibrium (LTE) radiance sources are treated in a consistent formalism, applicable to all altitudes from the ground to the edge of outer space. NLTE processes include chemical reactions among species in the rarefied high altitude atmosphere, such as those initiated by daytime solar pumping or nighttime auroral electrons. High altitude NLTE effects due to the solar terminator, stratospheric warming, and polar mesospheric clouds are modeled in a
uniform approach, merging seamlessly with low altitude LTE effects such as cloud and aerosol scattering. Radiance structure due to stochastic temperature fluctuations are included using an analytical linear response model.
The centerpiece software tools of the Atmospheric Physics group are the radiation modeling codes MODTRAN® (for altitudes up to ~100 km) and SAMM® (for altitudes to 300 km). Our active research supports first principles investigations of chemical processes leading to excited molecular vibrational/rotational states, models of deterministic structures and their effects on high altitude radiance and target illumination, and models of lower altitude phenomena such as reflections from clouds and ocean surfaces.