Passive sonar flow processing employs two separate, but synergistic measurement techniques. The first technique measures volumetric flow rate by monitoring turbulent "eddies" within the process flow. The second technique measures the speed at which sound propagates through the fluid to provide compositional information.

SONARtrac flow meters use a patented approach, based on well-established and mature sonar array processing techniques, to measure the velocity of these turbulent eddies as they convect past an array of sensors.

By "listening" to the pressure fields associated with the movement of eddies, SONARtrac flow meters determine the speed at which these eddies travel past the array of sensors.
 
Volumetric flow rate is determined using a Reynolds number-based calibration procedure, which links the speed of the coherent turbulent structures to the volumetric flow rate.