ZigBee ultrasonic tank level sensor

I wish I could use it with my SmartThings in order to monitor my water tanks.

http://www.massa.com/commercial/sensors/m3-m3is-sensor-matrix/

Looks interesting… how does it work? I mean if you say using for water tanks I’m assuming you want to use it to measure the level of water left in the tanks. How does it get this measurement?