Aviation Electronics Technician 1 - Historic Naval Ships Association

CHAPTER 4ANTISUBMARINE WARFAREThe detection of enemy submarines is one of theNavy’s major problems today. There are many typesof equipment in use that aid in the detection andtracking of submarines. As an aviation electronicstechnician, you will need to understand the principlesused in these equipments. Once again, every effort ismade to discuss as many different platforms andequipments as possible.SONAR PRINCIPLESLearning Objective: Identify factors thataffect the behavior of a sound beam in water.The word sonar is derived from the initial lettersof SOund, NAvigation, and Ranging. The word sonaris used to describe equipment that transmits andreceives sound energy propagated through water.Airborne sonar equipment is commonly called“dipping sonar,” and is used aboard varioushelicopters. Sonobuoys, also a form of sonar, will bediscussed later in this chapter.The operating principles of sonar are similar tothat of radar, except sound waves are used instead ofradio frequency waves. When the sound wave strikesan object, some of the energy reflects back to thesource from which it came. Since the speed of thesound wave and the time it takes to travel out andback are known, range can be determined. Byknowing the direction from which the sound echo isreflected, the operator can determine the bearinginformation.is a watertight unit that is used to convert electricalenergy into acoustical energy and acoustical energyback into electrical energy. The transducer acts like aloudspeaker in an office intercom system, alternatelyconverting electrical energy into mechanical energyand mechanical energy into electrical energy. Thetransducer acts like an underwater loudspeaker duringtransmission and an underwater microphone duringreception. The sound waves produced by a sonartransducer are represented by the circular lines shownin figure 4-1. Refer to this figure as you read thefollowing text.When the diaphragm of the transducer movesoutward, it moves the water next to the diaphragm.This produces a high-pressure area or compression inthe water. When the diaphragm of the transducermoves inward, the water next to the diaphragm movesinward. Thus, a low-pressure or rarefaction isproduced in the water. As long as the diaphragm isvibrating, alternate compressions and rarefactionstravel outward from the transducer in the water. Thedistance between two successive rarefactions or twosuccessive compressions is the wavelength of theThe type of sonar equipment that dependsprimarily on a transmitted sound wave and thereception of an echo to determine range and bearingof a target is known as echo-ranging or active sonarequipment. Another type of sonar equipment isreferred to as listening or passive sonar. This type ofsonar uses the target as the sound source. Althoughmost sonar equipment can be used in either mode ofoperation, surface ships and aircraft generally use theactive mode, and submarines use the passive mode.In echo-ranging sonar equipment, the source ofthe sound wave is a transducer. The sonar transducerFigure 4-1.-Sound waves produced in water by a transducer.4-1