20.6.5.1 DAS Spectra ‘trace’ times
| Topic Version | 2 | Published | 04/16/2018 | |
| For Standard | PRODML v2.0 | |||
A DAS Spectrum object stores the start times of each FFT calculation window applied in the SpectraDataTimes array object. This is a 1D array that contains the times in microseconds in Unix time for each FFT window stored in the DAS spectrum object*. Note that the times in the 1D example array are 1/ OutputDataRate microseconds apart. The SpectraDataTime array object has two additional attributes describing the times of the FBE traces recorded in human readable time format for convenience of the user: StartTime corresponds to the first stored FBE trace time and EndTime corresponding to the last stored FBE trace time in this DAS FBE object.
Figure 20.6.5-2 shows an example where spectra data is generated at an OutputDataRate of 3.125 Hz (note that this is 1/16th of the DAS instrument ‘raw’ PulseRate of 50 Hz, and corresponds to the number of raw samples the calculation filter-window is shifted when calculating the FFT for each locus. The sample times in microseconds are stored in the SpectraDataTime array; They are relative to the StartTime of the raw recording. Figure 20.6.5.1-1 shows the SpectraDataTime array corresponding with the spectrum windows in Figure 20.6.5-2 in the example file.
