Geopsy: Waveform Units

In Geopsy, informations for Data Conversion are stored in the signal Database in various fields. These values are automatically set in the database when a signal is imported only if this information appears in the signal file. However, this information can be manually set by editing a Table or automatically using Set headers in the Edit menu.

A digitizer writes integer values called Counts on a digital support. In order to retrieve the physical unit of the recorded signal (velocity or acceleration), Counts should be converted to Units. The Unit type (m/s, m/s$^{2}$...) is defined in the AmplitudeUnit field. The first step is to correct from the digitizer that wrote a current in Volts coming from the sensor on the digital support in Counts. This conversion factor is defined in the CountPerVolt and redundantly in the VoltPerCount (inverse) fields. This information is more likely to be be given by the digitizer in the signal file than the following. The second step is to correct from the sensor response that turns vibrations (velocity or acceleration) into an electric current in Volt. This response factor is defined in the VoltPerUnit and redundantly in the UnitPerVolt fields. The multiplication of these factors is stored in the CountPerUnit and redundantly in the UnitPerCount fields. These fields cannot be modified by the user (read-only). For instance, for a recording in velocity, the conversion factor C is computed as follows:

Important warning: Conversion from Counts to physical Unit DOES NOT correct for the non-flat response of the sensor at low or high frequencies. This feature is currently not implemented in Geopsy.