[Scilab-users] FFT - upward continuation of a 2D grid
Rafael Guerra
jrafaelbguerra at hotmail.com
Thu Jul 26 17:53:18 CEST 2018
Hi Lester,
If I understood properly, for an even number of spatial input grid points along Nx and Ny, with regular spacing dx and dy, I think k should be computed from:
kx = dkx*(-Nx/2+1:Nx/2);
ky = dky*(-Ny/2+1:Ny/2);
with:
dkx = 1/Nx/dx;
dky = 1/Ny/dy;
Regards,
Rafael
-----Original Message-----
From: users <users-bounces at lists.scilab.org> On Behalf Of arctica1963
Sent: Thursday, July 26, 2018 3:54 PM
To: users at lists.scilab.org
Subject: [Scilab-users] FFT - upward continuation of a 2D grid
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
_______________________________________________
users mailing list
users at lists.scilab.org
http://lists.scilab.org/mailman/listinfo/users
More information about the users
mailing list