How To: Calculate the horizontal and directional gradient of gridded data

How to:

How to calculate the total horizontal gradient of a grid or grid gradient amplitude in a specific direction.

Environment:

Oasis Montaj v7.*. Previous versions follow same principle but refer to the Geosoft 'Menumap' for equivalent menu options:(Menu Map).

Resolution:

To calculate the gradient of amplitude of gridded data in a specific direction:

1. Use Grid and Image > Filters > Horizontal gradient.
2. Enter the desired angle, noting the definition of the angle. This is measured as positive from +X axis, so 90 degrees would be equivalent to gradient in the 000 bearing, or North direction (+Y axis).

To calculate the total horizontal gradient of amplitude of gridded data:

1. Use the method above to calculate gradient in +X (0) and +Y (90) directions.
2. Use Grid & Image > Grid Math to construct a simple equation... G0 = sqrt(G1*G1+G2*G2).
3. Assign created G1, G2 grids using the browse buttons to locate the two gradient grids, and enter a suitable name for G0 grid.

Note: this technique uses a spatial convolution filter. FFT Horizontal gradient filtering is available in our Geophysics module.