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    The KHFFILT program   version 1.1a (c) Markku Pirttijrvi
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The KHFFILT program can be used to perform Karous-Hjelt and Fraser filtering of
geophysical VLF (very-low-frequency) data. In VLF method two orthogonal
components of the magnetic field are measured, and normally the tilt angle, a,
and ellipticity, e, of the vertical magnetic polarization ellipse are derived.
Real (in-phase) and imaginary (quadrature) components, however, are traditionally
used in Scandinavia and also in KHFFILT program. These components are based on
the tilt angle and ellipticity as: Re= tan(a)x100 % and Im= ex100 %.

The KHFFILT program requires a PC with 32-bit Windows 9x/NT4/2000/XP operating
system and a graphics display of at least 1024800 resolution. Memory
requirements and processor speed and are not critical, since the program uses
dynamic memory allocation and the filtering (and contouring) is fast to perform
even on older slow computers. The KHFFILT program has a simple graphical user
interface (GUI) that can be used to change some parameters, to handle file input
and output, and to visualize the original and filtered VLF responses. The user
interface and the data visualization are based on the DISLIN graphics library.

The program requires following files: 

    KHFFILT.EXE    the executable file
    DISLIN.DLL     dynamic link library for the DISLIN graphics

The distribution file (KHFFILT.ZIP) contains also a short description file
(_README.TXT), this user's manual (KHFFILT_MANU.PDF) and an example data file
(EXAMPLE.DAT). To install the program, create a new directory and copy or unzip
(Pkzip/Winzip) the distribution files there. To be able to start the program from
a shortcut that locates in a different directory move or copy the DISLIN.DLL file
into the WINDOWS\SYSTEM folder or somewhere where a path always exists.

This version of 2LAYER uses the new version (8.2) of the DISLIN.DLL file.

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