gmeterpy.corrections.polar_motion

Polar motion correction.

This module contains the polar motion correction to the gravity observations.

Functions

get_polar_motion(time[, return_status])	Interpolate polar motions from the IERS for the given time.
polar_motion_correction(xp, yp, lat, lon[, …])	Polar motion correction.

get_polar_motion(time, return_status=False)

Interpolate polar motions from the IERS for the given time.

This function will automatically download IERS data and interpolate pole coordinates for the given time.

Parameters

• time (float, array, or astropy.time.Time object) – Julian Date or astropy.time.Time object.

• return_status (bool) – Whether to return status values.

Returns

• xp, yp (~astropy.units.Quantity) – Polar motion coordinates, in arcsec.

• status (str or list) – Status values (if return_status`=`True):

  • ’IERS_B’ pole coordinates are from IERS Bulletin B (final).

  • ’IERS_A’ pole coordinates are from IERS Bulletin A (preliminary).

  • ’OUT_OF_RANGE’ given time is out of IERS data range.

polar_motion_correction(xp, yp, lat, lon, radius=<Quantity 6378136. m>, delta=1.164)

Polar motion correction.

Parameters

• xp (Quantity) – x coordinate of the terrestrial pole.

• yp (Quantity) – y coordinate of the terrestrial pole.

• lat (Quantity) – Geocentric latitude of the observation point referred to IERS pole.

• lon (Quantity) – Geocentric longitude of the observation point referred to IERS pole.

• radius (Quantity, optional) – Geocentric radius. Default value is r = a = 6378136 m.

• delta (float, optional) – Gravimetric amplitude factor, default is 1.164.

Returns

delta_g_polar – Polar motion correction.

Return type

Quantity

Notes

Variations in the geocentric position of the Earth’s rotation axis (polar motion) cause deformation within the Earth due to centrifugal forces. The actual position of the rotational axis is referenced to the IERS pole and described by the pole coordinates. The gravity correction (pole tide) is expressed by, e.g. Wahr (1985) 1:

\[\Delta g = -\delta\omega^2\times r \times 2 \times \sin\phi\cos\phi\left(x_p\cos\lambda - y_p\sin\lambda\right)\quad [\textrm{ms}^{-2}]\]

where \(x_p,y_p\) – pole coordinates, \(\omega\) – mean angular velocity, \(r = a = 6 378 136\) [m] – equatirial radius of the Earth, \(\phi,\lambda\) – geocentric coordinates of the station, \(\delta = 1.164\) – is the amplitude factor for the elastic response of the Earth.

1

Wahr, J. M. ( 1985), Deformation induced by polar motion, J. Geophys. Res., 90( B11), 9363– 9368, doi:10.1029/JB090iB11p09363