The SR50ATH is a sonic distance sensor with an integrated external temperature probe and heater. Sonic sensors determine distance by emitting an ultrasonic pulse and then measuring the elapsed time between the emission and return of the pulse. The temperature probe allows the SR50AT series to output temperature-corrected values (speed of sound varies with temperature). The integrated heater prevents ice and rime from coating the transducer. Note: Campbell Scientific recommends model SR50AT-316SS-L for marine environments.