Recommendation ITU-R P.836

This Recommendation provides methods to predict the surface water vapour density and total columnar water vapour content on Earth-space paths.

Title	PDF	Latest approved in
Recommendation ITU-R P.836	[PDF]	2017-12
surface density and total columnar content
Current recommendation version (In force)		Date
Recommendation ITU-R P.836-6	[PDF]	12/2017
Recommendations implemented in ITU-Rpy		Date
Recommendation ITU-R P.836-6	[PDF]	12/2017
Recommendation ITU-R P.836-5	[PDF]	09/2013
Recommendation ITU-R P.836-4	[PDF]	10/2009
Recommendations not implemented in ITU-Rpy		Date
Recommendation ITU-R P.836-3	[PDF]	11/2001
Recommendation ITU-R P.836-2	[PDF]	02/2001
Recommendation ITU-R P.836-1	[PDF]	08/1997
Recommendation ITU-R P.836-0	[PDF]	03/1992

Introduction

Atmospheric water vapour and oxygen cause absorption at millimetre wavelengths especially in the proximity of absorption lines (see Recommendation ITU-R P.676). The concentration of atmospheric oxygen is relatively constant; however, the concentration of water vapour varies both geographically and with time.

For some applications, the total water vapour content along a path can be used for the calculation of excess path length and for the attenuation due to atmospheric water vapour, where the attenuation due to atmospheric water vapour is assumed to be proportional to the total water vapour content through its specific mass absorption coefficient.

This Recommendation provides method used for global calculations of propagation effects that require an estimate of surface water vapour density or total columnar content of water vapour and its seasonal variation, when more accurate local data are not available.

Module description

itur.models.itu836.change_version(new_version)

Change the version of the ITU-R P.836 recommendation currently being used.

This function changes the model used for the ITU-R P.836 recommendation to a different version.

Parameters:new_version (int) –

Number of the version to use. Valid values are:

• 6: Activates recommendation ITU-R P.836-6 (12/17) (Current version)
• 5: Activates recommendation ITU-R P.836-5 (09/13) (Superseded)
• 4: Activates recommendation ITU-R P.836-4 (10/09) (Superseded)

itur.models.itu836.get_version()

Obtain the version of the ITU-R P.836 recommendation currently being used.

Returns:version – Version currently being used. Return type:int

itur.models.itu836.surface_water_vapour_density(lat, lon, p, alt=None)

Compute the surface water vapour density along a path.

This method computes the surface water vapour density along a path at a desired location on the surface of the Earth.

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 time exceeded for p% of the average year
• alt (number, sequence, or numpy.ndarray) – Altitude of the receivers. If None, use the topographical altitude as described in recommendation ITU-R P.1511

Returns:

rho – Surface water vapour density (g/m3)

Return type:

Quantity

References

[1] Water vapour: surface density and total columnar content https://www.itu.int/rec/R-REC-P.836/en

itur.models.itu836.total_water_vapour_content(lat, lon, p, alt=None)

Compute the total water vapour content along a path.

This method computes the total water vapour content along a path at a desired location on the surface of the Earth.

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 time exceeded for p% of the average year
• alt (number, sequence, or numpy.ndarray) – Altitude of the receivers. If None, use the topographical altitude as described in recommendation ITU-R P.1511

Returns:

V – Total water vapour content (kg/m2)

Return type:

Quantity

References

[1] Water vapour: surface density and total columnar content https://www.itu.int/rec/R-REC-P.836/en