## Fourier Amplitude Spectra

### Fourier Amplitude Spectra

Hi everyone

What procedure is used in the Seismosignal to obtain the Fourier Amplitude spectra? Please explain required steps to calculate the Fourier Amplitude spectra of an input record in this software.

Thanks so much

What procedure is used in the Seismosignal to obtain the Fourier Amplitude spectra? Please explain required steps to calculate the Fourier Amplitude spectra of an input record in this software.

Thanks so much

### Re: Fourier Amplitude Spectra

Dear sam123,

Once you load the record, the Fourier Amplitude Spectrum and the Power Spectrum are automatically computed. Please refer to "Fourier and Power Spectra" page of SeismoSignal Help System for more information.

Once you load the record, the Fourier Amplitude Spectrum and the Power Spectrum are automatically computed. Please refer to "Fourier and Power Spectra" page of SeismoSignal Help System for more information.

Zoi Gronti

Seismosoft Srl.

Seismosoft Srl.

### Re: Fourier Amplitude Spectra

Dear z.gronti

Thank you for your response but I did not find a detailed description for the calculation of the fourier amplitude spectra in the page of SeismoSignal Help System. I would be grateful if you could guide me about that how is calculated fourier amplitude spectra in the seismosignal.

Thank you for your response but I did not find a detailed description for the calculation of the fourier amplitude spectra in the page of SeismoSignal Help System. I would be grateful if you could guide me about that how is calculated fourier amplitude spectra in the seismosignal.

- seismosoft
**Posts:**608**Joined:**06 Jul 2007, 04:55

### Re: Fourier Amplitude Spectra

Hello sam123,

You may find the description you are looking for in any good textbook or in the internet (e.g. see: https://en.wikipedia.org/wiki/Fast_Fourier_transform)

Seismosoft Support

You may find the description you are looking for in any good textbook or in the internet (e.g. see: https://en.wikipedia.org/wiki/Fast_Fourier_transform)

Seismosoft Support

### Re: Fourier Amplitude Spectra

Hello

How could I create Fourier Amplitute Spectrum for Dispplacement, from Seismosignal.

Seismosignal create FAS only for acceleration.

Yours Faithfully

How could I create Fourier Amplitute Spectrum for Dispplacement, from Seismosignal.

Seismosignal create FAS only for acceleration.

Yours Faithfully

### Re: Fourier Amplitude Spectra

I suppose there is nothing to prevent you from saving an integrated displacement history as a text file and loading that into SeismoSignal. I am not sure what units problems you might run into., however.

Tim Huff

### Re: Fourier Amplitude Spectra

Hey There. I am kinda lost. What is the unit of Fourier amplitude, calculated by SeismoSignal? My understanding is that the said unit should be g.s, meaning that Fourier amplitude times the frequency should give the corresponding value of Sa (g).

- Fanis_Moschas
**Posts:**5**Joined:**21 Aug 2018, 14:27

### Re: Fourier Amplitude Spectra

Hello Navid,

the amplitude units are same as the units of your time series (for example g, m/sec or whatever your units are) multiplied by seconds (the time interval unt). So in order to obtain the real amplitude for a specific frequency in your results you need to multiply the amplitude with 2 (due to the two sided shape of the Fourier transform results) and then divide it by the number of points of your time series and by the time step (dt in seconds).

Best Regards

Fanis Moschas

the amplitude units are same as the units of your time series (for example g, m/sec or whatever your units are) multiplied by seconds (the time interval unt). So in order to obtain the real amplitude for a specific frequency in your results you need to multiply the amplitude with 2 (due to the two sided shape of the Fourier transform results) and then divide it by the number of points of your time series and by the time step (dt in seconds).

Best Regards

Fanis Moschas

Fanis Moschas

Seismosoft Srl.

Seismosoft Srl.