Earth geomagnetic field models

Currently, there is only the IGFR model in this toolbox to compute the Earth geomagnetic field.

IGRF v12

There is a native Julia implementation of the International Geomagnetic Reference Field (IGRF) v12. This can be accessed by two functions:

• igrf12syn: This is the native Julia implementation of the original FORTRAN source-code with the same input parameters.
• igrf12: An independent (more readable) implementation of the IGRF model. However, it is not as fast as igrf12syn yet (~20% slower).

The igrf12 function has the following signature:

function igrf12(date::Number, r::Number, λ::Number, Ω::Number, T; show_warns = true)

It computes the geomagnetic field vector [nT] at the date date [Year A.D.] and position (r, λ, Ω).

The position representation is defined by T. If T is Val{:geocentric}, then the input must be geocentric coordinates:

1. Distance from the Earth center r [m];
2. Geocentric latitude λ ($-\pi/2$, $+\pi/2$) [rad]; and
3. Geocentric longitude Ω ($-\pi$, +$\pi$) [rad].

If T is Val{:geodetic}, then the input must be geodetic coordinates:

1. Altitude above the reference ellipsoid h (WGS-84) [m];
2. Geodetic latitude λ ($-\pi/2$, $+\pi/2$) [rad]; and
3. Geodetic longitude Ω ($-\pi$, $+\pi$) [rad].

If T is omitted, then it defaults to Val{:geocentric}.

Notice that the output vector will be represented in the same reference system selected by the parameter T (geocentric or geodetic). The Y-axis of the output reference system always points East. In case of geocentric coordinates, the Z-axis points toward the center of Earth and the X-axis completes a right-handed coordinate system. In case of geodetic coordinates, the X-axis is tangent to the ellipsoid at the selected location and points toward North, whereas the Z-axis completes a right-hand coordinate system.

If the keyword show_warns is true (default), then warnings will be printed to STDOUT.

julia> igrf12(2017.12313, 640e3, 50*pi/180, 25*pi/180, Val{:geodetic})
3-element StaticArrays.SArray{Tuple{3},Float64,1,3}:
 15374.385312809889
  1267.9325221604724
 34168.28074619655

julia> igrf12(2017.12313, 6371e3+640e3, 50*pi/180, 25*pi/180, Val{:geocentric})
3-element StaticArrays.SArray{Tuple{3},Float64,1,3}:
 15174.122905727732
  1262.6765496083972
 34210.301848156094

julia> igrf12(2022, 6371e3+640e3, 50*pi/180, 25*pi/180)
┌ Warning: The magnetic field computed with this IGRF version may be of reduced accuracy for years greater than 2020.
└ @ SatelliteToolbox ~/.julia/dev/SatelliteToolbox/src/earth/geomagnetic_field_models/igrf.jl:99
3-element StaticArrays.SArray{Tuple{3},Float64,1,3}:
 15167.758261587729
  1423.7811941605075
 34342.17638944679

julia> igrf12(2022, 6371e3+640e3, 50*pi/180, 25*pi/180; show_warns=false)
3-element StaticArrays.SArray{Tuple{3},Float64,1,3}:
 15167.758261587729
  1423.7811941605075
 34342.17638944679