Target strength

The target strength or acoustic size is a measure of the area of a sonar target. This is usually quantified as a number of decibels. For fish such as salmon, the target size varies with the length of the fish and a 5 cm fish could have a target strength of about -50 dB.^[1]

Sonar image of the wreck of USS O-9.

Target strength (TS) is equal to 10 log₁₀(σ_bs/(1 m²)) dB, where σ_bs is the differential backscattering cross section. Backscattering cross section is 4πσ_bs.

References

1. J.E. Ehrenberg (1989), "A review of target estimation techniques", Underwater Acoustic Data Processing, Springer, ISBN 9780792301271

Further reading

• "Introduction to the use of sonar systems for estimating fish biomass, FAO Fisheries Technical Paper No. 191, Revision 1, FAO 1982"
• Fisheries Acoustics Simmonds, E John and MacLennan, David N (2005) Blackwell Publishing. ISBN 978-0-632-05994-2
• C. S. Clay & H. Medwin, Acoustical Oceanography (Wiley, New York, 1977)

target strength formula:

e.g. for a sphere with radius ${\displaystyle r}$ :

TS${\displaystyle =10\log(r^{2}/(4}$  m${\displaystyle ^{2}))}$  dB