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The spectra of fluctuations in variable [message #53004]

Wed, 14 March 2007 04:51

duxiyu@gmail.com
Messages: 88
Registered: March 2007

Member

I have a time series B(T).
The time resolution dt of the data is 4s and the amount N is 1000.
The unit of B and T is 'nT' and 's'.
I want to study its fluctuaions in frequence space using the power
spectral density (PSD).

BB=FFT(B)
freq=FINDGEN(N)/(N*dt)

Then I am not clear how to caculate the PSD.
Maybe, PSD=(ABS(BB))^2, but there is a problem in the unit.
The unit of BB is 'nT' that is the same as B, so the unit of PSD which
is obtained by the above method is 'nT^2'.
But in physical view the unit of PSD should be 'nT^2/Hz'.

The other question is how to caculate the phase difference between two
B1 and B2.
I caculate it by the following method, but I am not sure whether it is
right.

BB1=FFT(B1)
BB2=FFT(B2)
phase1=ATAN(BB1,/phase)
phase2=ATAN(BB2,/phase)
difference=phase1-phase2

Moreover, the angles seems not smoothed by regular method because of
theirs periodicity.
Is there other method to smooth the angle data?

Best wishes,
Du Jian

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[Message index]

		The spectra of fluctuations in variable By: duxiyu@gmail.com on Wed, 14 March 2007 04:51
		Re: The spectra of fluctuations in variable By: Craig Markwardt on Thu, 15 March 2007 08:20

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