IDL Help: FFT.PRO for Scrambling Spectral Components in X-Direction

[astrogirl123]

I have a spectrum with flux on the Y-axis and wavelength on the X-axis. What I want to do is take the Fourier transform of this spectrum. Then add a random phase between 0 and 2pi to the phase only. Then take the inverse Fourier Transform of this. The piece of code I wrote in IDL for a simple example is below. I was hoping to scramble up the spectrum by doing this. But I am not sure if I have achieved that goal. I have two questions

1. The final spectrum ( for some random phases) are vertically offset from the original spectrum. Why is that so?

2. The amplitude of the final signal varies a lot from the original spectrum for some phases. I wasnt expecting that either. why is that?

3. All I want is that the components of the original spectrum be jumbled up in the X-direction (ie the wavelength direction). How can it be done?

MY CODE :

n = 257
x = FINDGEN(n)
y = COS(x*!PI/6)*EXP(-((x - n/2)/30)^2/2)+x/50.

tek_color

yfft = fft(y)

magnitude = abs(yfft)
angle = ph(yfft)

for count=0, 300 do begin

rand = randomu(seed, 1)*2*!pi
randph = replicate(rand, 256)

fft_signal = magnitude*exp(complex(0,1)*(angle+randph))
ifft_signal = (fft(fft_signal, /inverse))

wait, 0.2

plot, x, y
oplot, x, (ifft_signal), color=2

endfor

end

 

[mmwave]

1. The vertical offset in the final spectrum is likely due to the random phase added to the original signal. When you add a random phase, you are essentially shifting the entire spectrum up or down in the y-axis, resulting in a vertical offset in the final spectrum.

2. The amplitude of the final signal varies because the random phase is affecting the magnitude of the original signal. Depending on the value of the random phase, the resulting amplitude can be higher or lower than the original signal.

3. If you want to only jumble up the components of the original spectrum in the x-direction, you can try taking the Fourier transform of the original spectrum, adding a random phase to the phase only, and then taking the inverse Fourier transform along the y-axis only. This will preserve the original spectrum in the x-direction while scrambling it in the y-direction. Alternatively, you can try using a different method, such as shuffling the data points in the x-direction, to achieve your desired result.