[Scilab-users] FFT - upward continuation of a 2D grid

[arctica1963]

Hello all,

A quick query regarding fft and wavenumber calculations. I am looking to do
an upward contuation of a gravity data grid using fft and the basic
equation:

fft_Grav_up = fft2(gravity_input) * e^(-kz) // think it also needs fftshif
to centre Zero?

... Upward_continued_gravity=ifft(fft_out_Grav_up)

Where z = upward continuation distance and k = wavenumber

k =sqrt(kx^2 + ky^2)

Is there an easy way to get the wavenumber from the input?

Before doing the fft, the grid would need padding on all edges, so I think
this works unless there is a better method:

dimx=size(xt)
dimy=size(yt)

// For FFT pad X,Y to 2*ncols, 2*nrows (large enough to avoid boundary
effects)

addedRows = dimy(1); addedCols = dimx(1);

tmp = [Boug_corr; Boug_corr($, :).*.ones(addedRows, 1)];
tmp = [tmp  tmp(:, $).*.ones(1,addedCols)];
tmp = [repmat(tmp(1, :), addedRows, 1) ; tmp];
Boug_corr_padded = [repmat(tmp(:,1), 1, addedCols) tmp]

After running fft, the grid would then be clipped back to the correct size.

If there is a simple code for doing this great!

Thanks
Lester



--
Sent from: http://mailinglists.scilab.org/Scilab-users-Mailing-Lists-Archives-f2602246.html