Recommendation ITU-R P.676¶

This Recommendation provides methods to estimate the attenuation of atmospheric gases on terrestrial and slant paths

Title	PDF	Latest approved in
Recommendation ITU-R P.676	[PDF]	2022-08
Attenuation by atmospheric gases and related effects
Current recommendation version (In force)		Date
Recommendation ITU-R P.676-13	[PDF]	08/2022
Recommendations implemented in ITU-Rpy		Date
Recommendation ITU-R P.676-12	[PDF]	08/2019
Recommendation ITU-R P.676-11	[PDF]	09/2016
Recommendation ITU-R P.676-10	[PDF]	09/2013
Recommendation ITU-R P.676-9	[PDF]	02/2012
Recommendations not implemented in ITU-Rpy		Date
Recommendation ITU-R P.676-13	[PDF]	08/2022
Recommendation ITU-R P.676-8	[PDF]	10/2009
Recommendation ITU-R P.676-7	[PDF]	02/0207
Recommendation ITU-R P.676-6	[PDF]	03/2005
Recommendation ITU-R P.676-5	[PDF]	02/2001
Recommendation ITU-R P.676-4	[PDF]	10/1999
Recommendation ITU-R P.676-3	[PDF]	08/1997
Recommendation ITU-R P.676-2	[PDF]	10/1995
Recommendation ITU-R P.676-1	[PDF]	03/1992

Introduction¶

This Recommendation provides the following three methods of predicting the specific and path gaseous attenuation due to oxygen and water vapour:

Calculation of specific and path gaseous attenuation using the line-by-line summation assuming the atmospheric pressure, temperature, and water vapour density vs. height;

An approximate estimate of specific and path gaseous attenuation assuming the water vapour density at the surface of the Earth;

An approximate estimate of path attenuation assuming the integrated water vapour content along the path.

These prediction methods can use local meteorological data, or reference atmospheres or meteorological maps corresponding to a desired probability of exceedance that are provided in other ITU-R P-series Recommendations. In the absence of local data, a combination of: a) the reference atmospheric profiles given in Recommendation ITU-R P.835 may be used, b) the mean annual global reference atmosphere given in Recommendation ITU-R P.835, c) the map of mean annual surface temperature in Recommendation ITU-R P.1510 and d) the maps of surface water vapour density vs. exceedance probability given in Recommendation ITU-R P.836 may be used in lieu of the standard ground-level surface water vapour density of 7.5 g/m3.

The method to compute an estimate of gaseous attenuation computed by a summation of individual absorption lines that is valid for the frequency range 1-1 000 GHz, and the method to compute a simplified approximate method to estimate gaseous attenuation that is applicable in the frequency range 1-350 GHz.

Module description¶

itur.models.itu676.change_version(new_version)[source]¶

Change the version of the ITU-R P.676 recommendation currently being used.

This function changes the model used for the ITU-R P.676 recommendation to a different version.

Parameters:

new_version (int) –

Number of the version to use. Valid values are:

12: Activates recommendation ITU-R P.676-12 (08/19) (Current version)

11: Activates recommendation ITU-R P.676-11 (09/16) (Superseded)

10: Activates recommendation ITU-R P.676-10 (09/13) (Superseded)

9: Activates recommendation ITU-R P.676-9 (02/12) (Superseded)

itur.models.itu676.get_version()[source]¶

Obtain the version of the ITU-R P.676 recommendation currently being used.

Returns:	version – The version of the ITU-R P.530 recommendation being used.
Return type:	int

itur.models.itu676.gaseous_attenuation_terrestrial_path(r, f, el, rho, P, T, mode)[source]¶

Estimate the attenuation of atmospheric gases on terrestrial paths. This function operates in two modes, ‘approx’, and ‘exact’:

‘approx’: a simplified approximate method to estimate gaseous attenuation that is applicable in the frequency range 1-350 GHz.

‘exact’: an estimate of gaseous attenuation computed by summation of individual absorption lines that is valid for the frequency range 1-1,000 GHz

Parameters:	r (number or Quantity) – Path length (km) f (number or Quantity) – Frequency (GHz) el (sequence, number or Quantity) – Elevation angle (degrees) rho (number or Quantity) – Water vapor density (g/m*3) P (number* or Quantity) – Atmospheric pressure (hPa) T (number or Quantity) – Absolute temperature (K) mode (string, optional) – Mode for the calculation. Valid values are ‘approx’, ‘exact’. If ‘approx’ Uses the method in Annex 2 of the recommendation (if any), else uses the method described in Section 1. Default, ‘approx’
Returns:	attenuation – Terrestrial path attenuation (dB)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gaseous_attenuation_slant_path(f, el, rho, P, T, V_t=None, h=None, mode='approx')[source]¶

Estimate the attenuation of atmospheric gases on slant paths. This function operates in two modes, ‘approx’, and ‘exact’:

‘approx’: a simplified approximate method to estimate gaseous attenuation that is applicable in the frequency range 1-350 GHz.

‘exact’: an estimate of gaseous attenuation computed by summation of individual absorption lines that is valid for the frequency range 1-1,000 GHz

Parameters:	f (number or Quantity) – Frequency (GHz) el (sequence, number or Quantity) – Elevation angle (degrees) rho (number or Quantity) – Water vapor density (g/m3) P (number or Quantity) – Atmospheric pressure (hPa) T (number or Quantity) – Absolute temperature (K) V_t (number or Quantity (kg/m2)) – Integrated water vapour content from: a) local radiosonde or radiometric data or b) at the required percentage of time (kg/m2) obtained from the digital maps in Recommendation ITU-R P.836 (kg/m2). If None, use general method to compute the wet-component of the gaseous attenuation. If provided, ‘h’ must be also provided. Default is None. h (number, sequence, or numpy.ndarray) – Altitude of the receivers. If None, use the topographical altitude as described in recommendation ITU-R P.1511. If provided, ‘V_t’ needs to be also provided. Default is None. mode (string, optional) – Mode for the calculation. Valid values are ‘approx’, ‘exact’. If ‘approx’ Uses the method in Annex 2 of the recommendation (if any), else uses the method described in Section 1. Default, ‘approx’
Returns:	attenuation – Slant path attenuation (dB)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gaseous_attenuation_inclined_path(f, el, rho, P, T, h1, h2, mode='approx')[source]¶

Estimate the attenuation of atmospheric gases on inclined paths between two ground stations at heights h1 and h2. This function operates in two modes, ‘approx’, and ‘exact’:

‘approx’: a simplified approximate method to estimate gaseous attenuation that is applicable in the frequency range 1-350 GHz.

‘exact’: an estimate of gaseous attenuation computed by summation of individual absorption lines that is valid for the frequency range 1-1,000 GHz

Parameters:	f (number or Quantity) – Frequency (GHz) el (sequence, number or Quantity) – Elevation angle (degrees) rho (number or Quantity) – Water vapor density (g/m3) P (number or Quantity) – Atmospheric pressure (hPa) T (number or Quantity) – Absolute temperature (K) h1 (number or Quantity) – Height of ground station 1 (km) h2 (number or Quantity) – Height of ground station 2 (km) mode (string, optional) – Mode for the calculation. Valid values are ‘approx’, ‘exact’. If ‘approx’ Uses the method in Annex 2 of the recommendation (if any), else uses the method described in Section 1. Default, ‘approx’
Returns:	attenuation – Inclined path attenuation (dB)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.slant_inclined_path_equivalent_height(f, P, rho=7.5, T=298.15)[source]¶

Computes the equivalent height to be used for oxygen and water vapour gaseous attenuation computations.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	ho, hw – Equivalent height for oxygen and water vapour (km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.zenit_water_vapour_attenuation(lat, lon, p, f, V_t=None, h=None)[source]¶

An alternative method may be used to compute the slant path attenuation by water vapour, in cases where the integrated water vapour content along the path, V_t, is known.

Parameters:	lat (number, sequence, or numpy.ndarray) – Latitudes of the receiver points lon (number, sequence, or numpy.ndarray) – Longitudes of the receiver points p (number) – Percentage of the time the zenit water vapour attenuation value is exceeded. f (number or Quantity) – Frequency (GHz) V_t (number or Quantity, optional) – Integrated water vapour content along the path (kg/m2 or mm). If not provided this value is estimated using Recommendation ITU-R P.836. Default value None h (number, sequence, or numpy.ndarray) – Altitude of the receivers. If None, use the topographical altitude as described in recommendation ITU-R P.1511
Returns:	A_w – Water vapour attenuation along the slant path (dB)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gammaw_approx(f, P, rho, T)[source]¶

Method to estimate the specific attenuation due to water vapour using the approximate method descibed in Annex 2.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	gamma_w – Water vapour specific attenuation (dB/km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gamma0_approx(f, P, rho, T)[source]¶

Method to estimate the specific attenuation due to dry atmosphere using the approximate method descibed in Annex 2.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	gamma_w – Dry atmosphere specific attenuation (dB/km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gammaw_exact(f, P, rho, T)[source]¶

Method to estimate the specific attenuation due to water vapour using the line-by-line method described in Annex 1 of the recommendation.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	gamma_w – Water vapour specific attenuation (dB/km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gamma0_exact(f, P, rho, T)[source]¶

Method to estimate the specific attenuation due to dry atmosphere using the line-by-line method described in Annex 1 of the recommendation.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	gamma_w – Dry atmosphere specific attenuation (dB/km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en

itur.models.itu676.gamma_exact(f, P, rho, T)[source]¶

Method to estimate the specific attenuation using the line-by-line method described in Annex 1 of the recommendation.

Parameters:	f (number or Quantity) – Frequency (GHz) P (number or Quantity) – Atmospheric pressure (hPa) rho (number or Quantity) – Water vapor density (g/m3) T (number or Quantity) – Absolute temperature (K)
Returns:	gamma – Specific attenuation (dB/km)
Return type:	Quantity

References

[1] Attenuation by atmospheric gases: https://www.itu.int/rec/R-REC-P.676/en