TRANSDUCER HORIZONTAL 



303 



— ::i;.-K<! >;. o.>«>ao:'>'»«'-*o»««oix H«a>C'«K>o<' — *' « «»o<»woo<x)*»«o» 



a: 70 MILLISEC PING 



B:lO MILLISEC PING 



Figure 29. Comparison of reverberation from a 70 MS ping with that from a 10 MS ping. 



14.2.3 Unimportance of Multiple 

 Scattering 



The theoretical formulas of Chapter 12 are based 

 on the assumption that multiple scattering can be 

 neglected. Experiments designed to measure the 

 amount of multiple scattering are described in a 

 memorandum by UCDWR '* and sunmiarized below. 



The 24-kc, QCH-3 units were mounted 6 ft apart 

 with the long dimension horizontal in such a way 

 that the unit used as a hydrophone could be rotated 

 about a vertical axis. The unit used as a projector 

 was kept in a fixed position. Observations were made 

 with the receiving hydrophone at bearings of 0, 30, 

 60, and 90 degrees, relative to the bearing of the pro- 



jector axis. That is, the receiving hydrophone was 

 rotated so that it faced away from the projector, and 

 the sound received in it was measured. Ping lengths 

 of 15 msec were used, and 5 pings were averaged at 

 each bearing. If the two QCH-3 units had been highly 

 directive, interpretation of the observations would 

 have been straightforward. However, they were not 

 highly directive, so that the portion of the signal pro- 

 jected in the direction in which the receiver was 

 pointing could not be neglected. In order to evaluate 

 the data, therefore, the following procedure was 

 adopted. The expected signal in the receiving hydro- 

 phone was calculated from the known directivity 

 patterns of the hydrophone and projector, assuming 

 single scattering was taking place in the ocean. It is 



