Reduce to Magnetic Equator (REDE)

Use the Reduce to Magnetic Equator option to apply the reduction‑to‑equator filter.

Reduce to Magnetic Equator dialog options

IGRF
Date (YYYY/MM/DD)	Enter the date when the survey was conducted to automatically calculate and populate the inclination and declination of the IGRF field. A Calculate button appears to the right of the date entry once a valid date is provided. This field is optional.
Inclination	Geomagnetic inclination I, in degrees measured from the horizon.
Declination	Geomagnetic declination D, in degrees azimuth.
Amplitude correction inclination	Amplitude correction inclination I_a, in degrees. Default values: +20° in the northern hemisphere –20° in the southern hemisphere

Application Notes

Reduction to the equator is used in low magnetic latitudes to centre magnetic anomaly peaks over their sources. This process improves interpretability while preserving the geophysical content of the data.

Reducing data to the pole (REDP) produces a similar effect, but at low latitudes an additional amplitude correction is often required to prevent North-South dominant signals from overwhelming the results. Consequently, reduced‑to‑pole data may offer a less “honest” representation of the underlying field in these regions.

Reduction to the equator consists of two components:

Amplitude: sin(I)
Phase: i cos(I) cos(D-θ)

Because of the strong amplitude correction, features normal to the declination direction may be amplified excessively, producing a strong discontinuity in that direction.

By specifying a higher latitude for the amplitude correction only, this effect can be mitigated—though at the cost of under‑correcting amplitudes for features aligned with the declination direction.

If a date is entered to calculate the inclination and declination, and the grid does not have a coordinate system defined, you will be prompted to assign one. Once defined, the IGRF date and parameters become the values used in all other controls requiring them.

Field strength is only required for apparent susceptibility calculations, but it is recalculated together with inclination and declination in the other controls to ensure all values remain synchronized.

Reduce to the Magnetic Equator Equation and Condition

Where:

Geomagnetic inclination (°).

Geomagnetic declination (° azimuth).

I_a

Inclination for amplitude correction (never less than I). Default = ±20°.

If | I_a |< | I |, it is set to I.

Wavenumber Domain Variable Definitions


The following variables are used in the wavenumber domain:
k	Wavenumber increment, used to depict a radially symmetrical variable.	Where: np: number of points cs: cell size
μ	X-component of the wavenumber.
v	Y-component of the wavenumber.
r	Radial component of the wavenumber.
θ	Angular (polar) component of the wavenumber.