Zg. Sun et G. Gimenez, INFLUENCE OF TARGET COMPOSITION ON THE RELATIONSHIP BETWEEN ECHO ENERGY AND TARGET QUANTITY, The Journal of the Acoustical Society of America, 96(5), 1994, pp. 3080-3087
The knowledge of the relationship between echo energy and target quant
ity is essential for fish stock assessment by energy investigation of
echoes. The linearity principle of fisheries acoustics states that a l
inear relationship exists between the mean echo energy scattered by ra
ndomly distributed targets and the quantity of those targets. The vali
dity of the linearity principle depends not only on the number density
of targets under investigation, but also on their physical structure.
This is evidenced by a study of the echo energy scattered by a random
distribution of underwater spherical targets. Numerical results show
that under the same conditions (measuring system, signal frequency, ta
rget size, etc.), the Linearity principle may hold for spheres made of
one material (a fluid, for example), but fail for spheres made of oth
er materials (soft, rigid, and steel spheres in our case). In cases wh
ere the target number density is relatively high, the normalized total
scattering cross section of targets may be an important parameter in
determining whether the linearity principle holds. The interference of
direct echoes, the shadowing effect, and the second-order scattering
are taken into account in this work.