Propagation Models

By default, the link budget tool assumes the location of interest experiences the atmospheric attenuation given by models from ITU-R P. Recommendations. In particular, it uses the model implementation imported from the ITU-Rpy package. Nevertheless, it is possible to override the modeled values and specify the atmospheric attenuation directly through option --atmospheric-attenuation (see Propagation Options).

The atmospheric attenuation models include the effects of rain, clouds, atmospheric gases, and tropospheric scintillation. Each of these effects involves several ITU-R P. recommendations. For instance, the following recommendations are used to model the rain attenuation:

  1. ITU-R P.838-3: Specific attenuation model for rain for use in prediction methods (1992-1999-2003-2005).

  2. ITU-R P.618-13: Propagation data and prediction methods required for the design of Earth-space telecommunication systems (12/2017).

  3. ITU-R P.1511-2: Topography for Earth-space propagation modelling (08/2019).

  4. ITU-R P.839-4: Rain height model for prediction methods (09/2013).

  5. ITU-R P.837-7: Characteristics of precipitation for propagation modelling (06/2017).

The sequence used to predict the rain attenuation exceeded over 0.01% of an average year is as follows:

  1. Find the rainfall rate in mm/h exceeded for 0.01% of an average year on the specific location of interest using the model and the database provided by Recommendation ITU-R P.837-7.

  2. Using the carrier frequency, find the coefficients to obtain the rain attenuation per kilometer following Recommendation ITU-R P.838-3.

  3. Find the mean annual rain height at the given location, i.e., how high is the melting layer, where the frozen precipitation turns into liquid precipitation. Use the model and the database from Recommendation ITU-R P.839-4.

  4. Find the earth station’s height at the given latitude/longitude by interpolating on the database from ITU-R P.1511-2.

  5. Using the parameters from steps 2, 3, and 4, as well as the elevation, latitude, and carrier frequency, compute the effective slant path subject to rain attenuation using the procedure from Section 2.2.1.1 of Recommendation ITU-R P.618-13.

  6. Finally, multiply the attenuation in dB/km (from step 2) by the effective slant path subject to rain attenuation (from step 5) to obtain the final rain attenuation in dB.

Distinct procedures apply to the other forms of atmospheric attenuation. Section 2.5 from Recommendation ITU-R P.618-13 outlines the references used for each computation. Refer to the ITU-Rpy’s docs for further information.

linkbudget.propagation.atmospheric_attenuation(lat, lng, elevation, pol_skew, freq, availability, dish_size, dish_eff)[source]

Total attenuation due to multiple sources of atmospheric attenuation

A wrapper to obtain the total atmospheric attenuation through ITU-Rpy.

Parameters:

  • lat (float) – Earth station’s latitude in degrees.

  • lng (float) – Earth station’s longitude in degrees.

  • elevation (float) – Elevation angle in degrees.

  • freq (float) – Carrier frequency in Hz.

  • availability (float) – Target link availability within [95 to 99.999%].

  • dish_size (float) – Earth station’s dish diameter in m.

  • dish_eff (float) – Dish aperture efficiency within [0, 1].

Returns:

Total atmospheric attenuation in dB.

Return type:

float