Version 1.1b (c) 2009 by Markku Pirttijärvi 

The FOURPOT program is designed for frequency domain processing and analysis of two-dimensional (2D) potential field arising, in particular, from geophysical gravity and magnetic field measurements. The data can be irregularly or regularly sampled. The frequency domain operations include high pass, low pass and direction filtering, upward and downward continuation, pole reduction of magnetic data, 1.st and 2.nd degree vertical and horizontal (x and y directed) gradients, total horizontal gradient, total gradient (analytical signal) and tilt gradient. Pseudo-gravimetric and pseudo-magnetic fields as well as gravimetric and magnetic potentials can be computed also.

FOURPOT computes the discrete 2D Fourier transform using the fast Fourier transform (FFT) algorithm. The Fourier transform represents a sum of sine and cosine terms with different spatial frequencies (Kx and Ky) that are defined by data sampling (dx and dy) in x and y directions. The highest spatial frequency is the so-called Nyquist frequency (e.g., max(Kx) = 0.5/dx). The lowest frequency is based on the data coverage (e.g., min(Kx) = 0.5/(max(x)-min(x)). Considering that the inverse of the spatial frequency represents wave length (Lx = 1/Kx), zero frequency means infinite wave length, i.e., constant level of data. Because of the properties of the Fourier transform (symmetry, linearity, shift and derivate properties) several computational operations can be performed in Fourier transformed frequency (Kx, Ky) domain more efficiently than in the spatial (x, y) domain. For more detailed information about Fourier transform methods in potential field analysis, please, see Blakely (1995), for example.

Here is a screen dump of the the FOURPOT program (120 kB).

This basic version of FOURPOT is a 32-bit application that can be run on Windows 98/XP/Vista system with a graphics display of at least 1024 768 pixel resolution. Memory requirements and processor speed and are not critical, unless very large data sets are used. The program has simple graphical user interface (GUI) that is used to handle file input and output, to perform the computational operations, and to visualize the data and the results. The user interface and the data visualization are based on the DISLIN graphics library.

Here you can download the FOURPOT.ZIP distribution pagage (2.3 MB).

The distribution file (FOURPOT*.ZIP) also contains a description file (_README.TXT), user's manual (FOURPOT_MANU.PDF), and some example data files (*.DAT). To install the program uncompress (e.g., Winzip or 7Zip) the distribution file and move the resulting FOURPOT folder to preferred place (e.g., C:\TOOLS). To be able to start the program from a shortcut that locates in a different directory or from the desktop you should move or copy the DISLIN.DLL file into the WINDOWS\SYSTEM (or SYSTEM32) folder or somewhere along the system path.

See the user's guide (FOURPOT_MANU.PDF) file for further information (1.5 MB).