Pseudo-Gravity (GPSD)

Use the Pseudo-Gravity option to apply a pseudo-gravity filter.

Pseudo-Gravity Filter dialog options

Date (YYYY/MM/DD)	Enter the date when the survey was conducted. The geomagnetic inclination and declination of the IGRF field are automatically calculated and populated. A Calculate button appears to the right of the date field after a valid date is entered. This field is optional.
Inclination	Geomagnetic inclination (I), in degrees measured from the horizon.
Declination	Geomagnetic declination (D), in degrees azimuth.
Density contrast	Density contrast (d), in g/cm3. (Default = 1.0).
Magnetization	Magnetization (J), in nT. (Default = 50,000).
Amplitude correction inclination	Inclination Ia used for amplitude correction. Default value: ±20°. If | Ia | is entered as less than | I |, it is automatically set to I.

Application Notes

Typically, the input to this filter is a TMI (Total Magnetic Intensity) grid. However, you may also begin with a pole‑reduced grid.

In that case:

• Set the inclination to 90°

• Declination is irrelevant and may be set to 0°

Pseudo-Gravity Equation and Condition

Where:

I	Geomagnetic inclination.
Iɑ	Inclination used for amplitude correction (never less than I). Default = ±20°. If | Iɑ | < | I |, it is set to I.
d	Density contrast in g/cm3.
G	Gravitational constant (6.6738).
J	Magnetization in nT.
D	Geomagnetic declination.

Parameters:

q	Direction of the wavenumber, in degrees azimuth.
r	Wavenumber, in radians per ground unit. r=2πk Where k is in cycles per ground unit.

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.

Output Units

Output pseudo‑gravity is:

• mGal, if the ground unit is metres, or

• 0.3 mGal, if the ground unit is feet.