|Title||Extrapolating Green's functions using the waveguide invariant theory|
|Publication Type||Journal Article|
|Year of Publication||2020|
|Authors||Song HC, Byun G.|
|Type of Article||Article|
|Keywords||acoustics; array; Audiology & Speech-Language Pathology; blind deconvolution; field; localization; phase; range; sound; surface ship; time-reversal|
The broadband interference structure of sound propagation in a waveguide can be described by the waveguide invariant, beta, that manifests itself as striations in the frequency-range plane. At any given range (r), there is a striation pattern in frequency (omega), which is the Fourier transform of the multipath impulse response (or Green's function). Moving to a different range (r+Delta r), the same pattern is retained but is either stretched or shrunken in omega in proportion to Delta r, according to Delta omega/omega = beta(Delta The waveguide invariant property allows a time-domain Green's function observed at one location, g(r,t), to be extrapolated to adjacent ranges with a simple analytic relation: g(r+Delta r,t)similar or equal to gr,alpha(t-Delta r/c)), where alpha=1+beta(Delta r/r) and c is the nominal sound speed of 1500 m/s.The relationship is verified in terms of range variation of the eigenray arrival times via simulations d by using real data from a ship of opportunity radiating broadband noise (200-900 Hz) in a shallow-water environment, where the steep-angle arrivals contributing to the acoustic field have beta approximate to 0.92. (C) 2020 Acoustical Society of America.