Geopsy: Window Length
Setting the window length for an individual analysis window is needed in several contexts. It is needed for both Spectrum and H/V computation as well as for any array processing technique, let it be FK, HRFK or MSPAC.
You will find therefore the Window Length element in all toolboxes related to the analysis methods mentioned above
within the General section of the Time tab. The example shows the General section of the
frequency wavenumber toolbox. There are (up to) three options provided in a drop box 
.
- Exactly (takes exactly the time window length as provided in the corresponding editable box - unit is in seconds).
- At least (takes at least the time window length as given in the editable box, if possible it takes more - unit is in seconds).
- Freq. dep. (read: frequency dependent. Scales window length to the center frequency of each frequency band to be processed. The number given in the editable box corresponds to a window length in number of cycles for each frequency band. T is the center period of the band).
Note: for Spectrum and H/V toolboxes, only the options At least and Exactly are implemented. Freq. dep. is of no use in this context. On the contrary, currently for array processing toolboxes FK, HRFK or MSPAC, the most reasonable and only implemented setting for the Length parameter in the context of narrowband dispersion curve processing is Freq. dep.. This option relates the window length to the center frequency of each frequency band to be processed. The absolute window lengths for analysis are therefore linked to the settings in the frequency selection.
Example: for a frequency band with center frequency 2.5 Hz, the central period is 1/2.5 = 0.4 s. Therefore, with a frequency dependent Length setting of 30.00 T, the window length will be chosen as 12.00 s. In upcoming versions of geopsy software, this combo box entries in the different toolboxes will be adjusted to the reasonable options.
