464 



MECHANICAL AND ACOUSTICAL SENSES 



As an example, consider the following calculation for a signal of 40 kHz, 

 the DuKane receiver (BW estimated 500 Hz, DI = 16 dB), a sea state of 2 

 (Ns = 33 dB re 1 juPa + estimated 5 dB for coastal conditions = 38 dB 

 re 1 yuPa), and an RD of 3 dB: 



MDS = 38+10 log 500 -16 + 3 

 = 38+ 10 (2.7) -16 + 3 

 = 38 + 27-16 + 3 

 = 52 dB re 1 juPa. 



Therefore, since the receiver absolute sensitivity limit of 45 dB re 1 juPa 

 is lower, the effective MDS will be the 52 dB re 1 juPa value as calculated 

 above. 



Signal -Detection Range— If the above MDS value is used, a theoreti- 

 cal range can be calculated for any given transmitter by starting with its 

 known signal strength and applying the estimated transmission losses. This 

 can be done in tabular form, as shown in Table 7 for the Mark V shark trans- 

 mitters, which emit 40-kHz pulses at a level of about + 172 dB re 1 juPa 

 at 1 m. 



Thus, according to Table 7, the transmitter's signal will diminish to the 

 MDS level of 52 dB re 1 [iPa at approximately 5 km. However, since Table 7 



Table 7. Diminution of signal strength with distance, considering losses due 

 only to spreading and absorption, for a transmitter source level of + 172 dB 

 re 1 /LtPa at 1 m. 



*From Table 3. 



