The target strength or '' acoustic size'' is a measure of the area of a

sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances ( ranging), communicate with or detect objects on ...

target. This is usually quantified as a number of

decibels The decibel (symbol: dB) is a relative unit of measurement equal to one tenth of a bel (B). It expresses the ratio of two values of a power or root-power quantity on a logarithmic scale. Two signals whose levels differ by one decibel have a pow ...

. For fish such as

salmon Salmon () is the common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of ...

, the target size varies with the length of the fish and a 5 cm fish could have a target strength of about -50 dB. Target strength (TS) is equal to 10 log₁₀(''σ''_bs/(1 m²)) dB, where ''σ''_bs is the differential

backscattering In physics, backscatter (or backscattering) is the reflection of waves, particles, or signals back to the direction from which they came. It is usually a diffuse reflection due to scattering, as opposed to specular reflection as from a mirror, ...

cross section Cross section may refer to: * Cross section (geometry) ** Cross-sectional views in architecture & engineering 3D *Cross section (geology) * Cross section (electronics) * Radar cross section, measure of detectability * Cross section (physics) **Ab ...

Backscattering cross section Backscattering cross section is a property of an object that determines what proportion of incident wave energy is scattered from the object, back in the direction of the incident wave. It is defined as the area which intercepts an amount of power ...

is 4π''σ''_bs.

References

Further reading