PERTURBATIONS

Perturbations is part of the PERSEO Aresys python project, and it's aimed at computing geophysics displacements (Plate Tectonics, Solid Earth Tides) and atmospheric (Ionospheric, Tropospheric) signal delays.

Atmospheric Perturbations

This module relies on resources files that have been downloaded and attached to this project in order to properly perform atmospheric computations. In particular, tropospheric VMF3 model legendre coefficients and stations grid points coordinates (both for 1x1 and 5x5 grids) have been added as separate files in the resources module and actively use in the code.

These files can be found here:

VMF3 Legendre coefficients: https://vmf.geo.tuwien.ac.at/codes/vmf3.m

Station coordinates grid 1x1: https://vmf.geo.tuwien.ac.at/station_coord_files/gridpoint_coord_1x1.txt

Station coordinates grid 5x5: https://vmf.geo.tuwien.ac.at/station_coord_files/gridpoint_coord_5x5.txt

Geodynamics Perturbations

To estimate Earth Solid Tides, this package relies on a python wrapper implementation of the solid.for Fortran code by Dennis Milbert¹.

Program Solid is based on an edited version of the dehanttideinelMJD.f source code provided by Professor V. Dehant. This code is an implementation of the Solid Earth Tide computation found in section 7.1.2 of the IERS Conventions (2003)², IERS Technical Note No. 32.

Plate Tectonics displacement correction is based on the ITRF2014 plate motion model³.

Geomagnetic Field

The International Geomagnetic Reference Field (IGRF) is a collaborative model produced by geomagnetists and endorsed by the International Association of Geomagnetism and Aeronomy (IAGA). It's a standard mathematical description of the Earth's main magnetic field that is used widely in studies of the Earth's deep interior, its crust and its ionosphere and magnetosphere.

The IGRF is updated every five years, and currently can estimate the field from 1900 to 2030. Currently the IGRF is described through a spherical harmonic model up to 13th degree.

The implemented model is the 14th IGRF iteration, released in October 2024⁴. It let the user compute the magnetic field components at given points in space and time, both in geocentric and geodetic coordinates.