Geopsy: Multiply

Multiply, reached from the Waveform menu, multiplies the signals in the active signal viewer by a constant value. This is especially useful for data conversion from counts to velocity or acceleration, for example. By clicking on Multiply, a pop-up window appears and lets the user enter the value of the multiplication factor.

"Multiply" modifies the temporary signals in the active viewer.

Data Conversion

Currently, signals are not converted or corrected by the response file of the acquisition system when imported in Geopsy. "Multiply" is the only way to convert data from counts or volts delivered by the digitizer into velocity or acceleration. For a recording in velocity, the conversion factor C is computed as follows:

$C[(m/s)/count]={\frac {StationConversion[V/count]}{Gain[-].SensorSensitivity[V/(m/s)]}}$.

StationConversion is the gain of the station, it represents the inverse of the number of counts used by the station to write a 1 Volt value delivered by the sensor. It may depend on the sampling frequency. Depending on the digitizer it may also be modified by a manual Gain (power of 2) used to adapt the number of bits used to maximize it depending on the signal amplitude. SensorSensitivity is the sensitivity of the sensor, i.e. the number of Volts output for a unit m/s velocity.

Examples of conversion factors

• Quanterra Q330 digitizer with Lennartz 5s sensor: $C=5.96047e-9[(m/s)/count]$
• Nanometrics Taurus digitizer with Kinemetrics Episensor accelerometer: $C=1.58946e-9[(m/s^{2})/count]$