ITU-R P676 Atmospheric Absorption Model
This model implements the ITU-R atmospheric absorption loss model. You can choose either version 9 or version 13, which is the latest update to the model. It supports 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.
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 1-350 GHz | 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 Section 2.2 Water Vapor Method | Select this check box to implement the water vapor attenuation equations found in Section 2.2 of the ITU-R P676-13 model. This check box defaults to not selected, meaning that the model will implement Section 2.1 equations. |
| Atmospheric Data |
Select one of the following options for determining barometric pressure, temperature, and water vapor density for the model:
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The Ansys Systems Tool Kit® STK® application only implements the instantaneous prediction methods in Version 13.