Re: [ferret_users] FFT.

[Ryo Furue <furue@xxxxxxxxxx>]

Hi,

> I am trying to calculate the FFT for a data set which has irregular axis

I'm no expert, but I think the FFT algorithm works only for
evenly-spaced gridded data.  If so, what you need is to map your data
on to an evenly-spaced grid.

Mapping inevitably introduces leaks (aliasing) in the frequency domain
and if your problem is sensitive to aliasing, you would have to
carefully choose an appropriate mapping.  If, on the other hand, you
aren't concerned about a bit of aliasing, you can just use Ferret's
capability of regridding.  Look at the Ferret manual for regridding.

For general information about Fourier transforms of unevenly-spaced
data, google-search for "FFT uneven grid" without the quotation marks.

Hope this helps,

Ryo