D. R. Raichel
Dept. of Mech. Eng., Albert Nerken School of Eng., The Cooper Union, 51 Astor Pl., New York, NY 10003
The possibility exists that cetaceans can assess undersea environment through their sensing the modification of their probe signals in terms of harmonic content as well as the intensity of the reflected signals. The fluidic constitutivity or the elasticity (or a combination thereof) of the impinged surrounding objects affect the cetaceans' probe signals so that additional harmonics appear in specific ways in the reflections. Absorptivity, spatial distribution, and the distance and acoustic impedance between the emitter and the reflector constitute the other factors that affect the probe signals. The harmonics aspect of this theory derives from previous work in the study of sound propagation through rheological fluids [D. R. Raichel and W. H. Kapfer, J. Appl. Mech. (Ser. E) 40, 1--6 (1973); M. Sokolov, ibid. 41, 823--825 (1974)], whereby perturbation techniques are applied to acoustic equations to yield the higher harmonics that result spontaneously from the inherent nonlinearity of sound wave travel through a constitutively real medium.