Aviation Electronics Technician 1 - Historic Naval Ships Association

Figure 4-7.-Transducer installed on a moving ship.If the transducer is aimed perpendicular to thedirection of motion, the particles in the water willecho the same note sent out because the transducer isneither going toward the particles nor away fromthem. (See figure 4-7.)Now consider the echo from the submarine,shown in figure 4-8. Again, the transducer is shownstationary. When the submarine is neither goingtoward nor away from the transducer, it must be eitherstopped or crossing the sound beam at a right angle.If it is in either condition, it reflects the same sound asthe particles in the water. Consequently, thesubmarine echo has exactly the same pitch as thereverberations from the particles.Figure 4-9.-Comparison of echo frequency and reverberationfrequency when submarine moves toward transducer.Suppose that the submarine is going toward thetransducer, as shown in figure 4-9. It is as though thesubmarine is the train heading toward the car that isblowing its horn at the crossing. The horn soundshigher as the train approaches the car. In the samemanner, the sound beam sounds higher to thesubmarine as it approaches the transducer.Figure 4-8.-Transducer supported by helicopter. Dopplereffect is absent when submarine is stationary or moves atright angles to sound beam.Figure 4-10.-Comparison of echo frequency andreverberation frequency when submarine moves awayfrom transducer.4-8