Fraser Filter
From Wikipedia, the free encyclopedia
A Fraser Filter is typically used in Geophysics when displaying VLF (Very Low Frequency) data. It is effectively the first derivative of the data.
If f(i) = fi represents the data you collected then
average12 = (f1 + f2) / 2
is the average of two values.
Consider this value to be plotted between point 1 and point 2 and do the same thing with points 3 and 4:
average34 = (f3 + f4) / 2
If deltaX represents the space between each station along the line then
(average12 - average34) / (2 * deltaX)
= ((f1 + f2) - (f3 + f4)) / (4 * deltaX)
is the Fraser Filter of those four values.
Since 4 * deltaX is constant, you can ignore it and consider the Fraser Filter to be (f1 + f2) - (f3 + f4)
