Fast Fourier Transformation

The Fast Fourier Transformation (FFT) converts the RA, DEC, and seismic data from the time domain to the frequency (upper adjacent graph) and wave period domains (lower adjacent graph). This allows to identify vibration sources based on their frequency or wave period. As the RA and DEC data are also converted the tool allows to see if there is correlation between the vibrations and mount data. In the upper right hand corner the actual data frequencies are displayed in the colours of the graphs.
The frequency range of the FFT depends on the frequency at which data is collected. The Nyquist–Shannon sampling theorem tells us that the maximum detectable frequency in a signal is half the sampling frequency. The means that using the 20Hz seismic data frequencies of maximum 10Hz can be detected in them, while for the RA and DEC data the limitation is around 2Hz (depending on comuputer and network speeds).

The graphs are scaled automatically to the most significant data upon opening of the FFT window. Using the + and - button the horizontal scale can be changed to zoom into or out of the data. The < and > buttons allow to shift the graph to the left or right.

Once the FFT window is openened graphs will be stored on disc at the same pace as the RA, DEC and seismic graphs.