ITU-R P676-9 Atmospheric Absorption Model

This model implements the latest update to the ITU-R atmospheric absorption loss model. It continues to support the options for the fast approximate model and the seasonal/regional atmospheric model. The maximum height for this model is 100 km.

The ITU model performs ray tracing on a propagation path. The intervening atmosphere is broken up into concentric shells, and computes line segments within each shell along the propagation path. The specific attenuation along each segment is computed and multiplied by the length of the segment. Finally, all segments are added to arrive at a total attenuation value.

This model supersedes all previous releases of the atmospheric absorption loss model.

The ITU recommendation specifies two different atmosphere models and two different specific attenuation calculations, which are controlled via the following options:

Option	Description
Use Fast Approx. Method	Uses an empirical curve-fit model valid over the frequency range 1-350 GHz. Otherwise, a highly accurate physics-based model is used which accounts for the effects of each constituent spectral line (1-1000 GHz).
Use Seasonal/Regional Atmosphere Method	Uses a season and latitude-dependent model. Otherwise, a global reference atmosphere model is used.