Uniden Clock manual Understanding Sonar, AIR Echoes

UNDERSTANDING SONAR

All depth sounders emit ultrasonic sound signals from the transducer into the water located under your boat. These sound signals travel through the water at a rate of approximately 4,800 feet per second (1500 meters per second). The depth sounder transmits a signal and receives a returning echo. The unit calculates the amount of time in microseconds that elapsed while the signal traveled down to the bottom and returned back to the transducer. This time is then converted to depth and displayed on the screen.

It may help to understand these sound signals traveling between the transducer and the bottom by imagining a ping-pong ball bouncing up and down from the floor. The closer the ball is to the floor, the less time it takes for it to return. The higher the ball is bounced, the longer it takes to return. Bouncing the ball off a hard surface such as cement is the same as bouncing a signal off a sandy or hard bottom. Bouncing this same ball off carpeting creates a totally different effect because the ball returns with less force. The same principle applies to an echo bouncing off a muddy or grassy bottom, causing the echoes to be weaker.

AIR ECHOES

Air echoes can be caused by excessive turbulence under the face of the transducer. Ultrasonic signals from a transducer will not penetrate air. They react to air in the same manner as they react to a hard bottom described above. Therefore, if your transducer is not mounted properly and you are getting turbulence (air bubbles) under your transducer, you may get false readings. This is simply because signals are being returned by the turbulence and are never reaching the bottom.

14