A mobile geophysical instrument produces geophysical data sets each associated with a position computed by use of a position sensor. A variable time delay results between a time when data for each geophysical data set is collected and a time when a position associated with each geophysical data set is recorded. A module receives distance transducer data and includes circuitry configured to generate a module signal based on trigger signals from the distance transducer and a calibration value. A data acquisition system (DAS) receives geophysical data sets from the geophysical instrument, positioning data from the positioning sensor, and the module signals. The DAS generates a DAS timestamp in response to each module signal and associates the DAS timestamp with each geophysical data set and a position associated with the geophysical data set, so as to substantially eliminate the variable time delay.