Raditive Transfer

rtRadiative transfer modeling simulates the propagation of electromagnetic radiation through a medium, such as the atmosphere or the ocean. There are a number of physical phenomena that affect the path of radiation, including absorption, scattering and radiative emissions. Atmospheric radiative transfer modeling requires a detailed description of the properties of the atmosphere, including pressure, temperature, humidity, molecular concentrations and aerosol characteristics. The applications for atmospheric radiative transfer models are wide-ranging, including for example forward modeling of remote sensors, accurate retrieval of remotely-sensed information, calculation of parameters for atmospheric correction of remotely-sensed imagery, and support of synthetic scene generation.

Atmospheric Effects on Transfer of Heat and Environmental Radiation (AETHER™)

The AETHER™ software product is a band-model atmospheric radiative transfer code developed from the Department of Defense standard model Moderate Spectral Atmospheric Radiance and Transmission (MOSART). AETHER™ solves the radiative transfer equation in a fully three-dimensional, spatially varying atmosphere, and outputs the full radiative environment for any spectral band in the ultraviolet through microwave spectral regions (0.2 μm to infinity, or 0-50,000 cm-1). AETHER™ uses the same molecular band model as MODTRAN® 5, derived from the HITRAN 2008 database, to provide spectral sampling options of 15 cm-1, 5 cm-1, 1 cm-1 and 0.1 cm-1. Radiative effects modeled include absorption, emission, reflection, transmission, single scattering, multiple scattering and turbulence. Multiple scattering is modeled using an exponential sum fit algorithm. Radiative outputs include path radiance, solar/lunar irradiance, skyshine, and transmission, all as a function of altitude. Terrain material temperatures for a large number of materials can also be calculated for the given atmospheric conditions. Environmental characterization is provided by an extensive set of global databases incorporated into the AETHER™ code, including terrain elevation, water/snow compositions, ecosystem type, soil types and properties, urban center locations and population densities, climatology atmospheric profiles from the Earth’s surface to the tropopause, and hydrology. AETHER™ provides 18 aerosol models and 23 model atmospheres with seasonal variations, and allows customization of these models through scalable profiles (water vapor, carbon dioxide, ozone, haze) and variable climatologies (temperature, humidity, wind). For cases where this is still not sufficient AETHER™ allows full customization through user-defined three-dimensional atmospheres. In addition, AETHER™ includes several cloud, rain and fog (hydrometeors) models which can be requested by the user. AETHER™ supports a wide variety of viewing geometries, including Earth-based, space-based and airborne. Multiple geometries can be included in a single execution of the code, each for a different time of day, making AETHER™ a fully four-dimensional code.

AETHER™ can be used for calculating accurate and realistic atmospheric transmission and radiance along sensor-target line-of-sight paths as well as calculating optical radiance backgrounds against which targets are detected by sensor systems. This provides the capability to support both scene and signature simulations. Currently CPI uses AETHER™ to support both the Atmospheric Correction Tool (ACT) and the scene simulation models GAIA™ and OCEANUS™.

Moderate Spectral Atmospheric Radiance and Transmittance (MOSART)

MOSART is a U.S. Department of Defense (DoD) standard code for predicting the radiative environment in the UV/VIS/IR/MMW. MOSART is extensively used to provide input for scene and signature simulations in packages such as the Synthetic Scene Generation Model (SSGM). Like AETHER™, MOSART provides atmospheric transmission along sensor-target line-of-sight paths, optical radiance backgrounds (e.g., terrain, clouds, limb, and space) against which targets are detected by sensor systems, and appropriate irradiances (e.g., solar, lunar, earthshine, skyshine). However, MOSART uses an older molecular band parameters database derived from the HITRAN 1996 database, and allows options only for 1 cm-1 sampling and millimeter wave capability. MOSART was most recently funded and distributed by the U.S. Naval Research Laboratory (NRL), however currently CPI is the only approved distributer for the MOSART code. MOSART v2.0.4 is available for download from the CPI website.