EOIR Atmosphere Model

Use to turn on and off the Earth's atmosphere and define the atmosphere parameters.

To access the EOIR Atmosphere Model, click Atmosphere Definition... from the EOIR Configuration window.

Atmosphere Modes

Select one of the following atmosphere models turn on the Earth's atmosphere.

MODTRAN

The MODTRAN-based atmosphere model is one of the highest fidelity, community standard, atmospheric models available in EO/IR.

Simple Atmosphere

This atmosphere model calculates the following atmospheric properties at the wavelengths corresponding to the Spectral Band Edges, and at a spectral resolution specified by the Number of Intervals set on the Sensor's EOIR Spectral Properties page:

Transmission - what gets through the atmosphere after light is differentially absorbed and scattered out of the light ray.
Scatter In - light scattered into the ray by Rayleigh and Mie aerosol scattering. Rayleigh scattering is what makes the sky blue. Mie aerosol scatter is what adds the white haze.
Path Radiance - infrared emission of the atmosphere into the ray.

The amount of atmosphere traversed by a ray affects the above calculations. This value is calculated for all atmospheric geometries of sensor and target location, except for space to atmosphere to space.

EOIR does not currently calculate the atmospheric limb, but it is targeted for a future release of EOIR.

All of the preceding calculations utilize the US Standard 1976 atmospheric layer model to specify data such as temperature and pressure by altitude layer. This is similar to calculating an annual average of the atmosphere in the central United States.

The Simple Atmosphere model only utilizes variations of atmospheric properties with altitude. The horizontal variations, that constitute weather, are not calculated. Clouds are not calculated in the current model, but are targeted for a future release of EOIR.

The atmospheric spectral resolution used in scene generation is the lesser of EOIR's maximum atmospheric spectral resolution, shown below, or the one resulting from the selected EOIR Spectral Properties "Number of Intervals" within the selected spectral band.

For more details on SNR computations, see the EOIR Model Description and Validation document.

4.3.1.1 Simple Atmosphere
6.2.5.4 Atmosphere - MODTRAN 4 Comparison

Atmosphere Parameters

The Atmosphere Parameters provide some control over the atmosphere's physical characteristics.

Aerosol Models. Select the type of aerosol model to be used by the Simple Atmosphere model. Aerosols are tiny particles in the air that cause whitish haze visible to the human eye. Each aerosol model is a distribution of particles of different sizes and how light interacts with them. For instance, in a Maritime atmosphere, salt crystals, from wind and wave action, are a major contributor to aerosols.

Visibility. The meteorological visibility in km. Meteorological visibility is the greatest distance at which a black object of suitable dimensions, located near the ground, can be seen and recognized when observed against a bright background.

Humidity. Relative humidity expressed as a percentage from 0.0 to 100.0.