Inversion of the depth, thickness, and absorption coefficient of a layer of fish (anchovies) from transmission loss measurements in the Yellow Sea

Abstract

Estimates of bioacoustic parameters of fish (anchovies) and geoacoustic parameters of the bottom were simultaneously inverted from the TL measurements of Qiu et al. (1999) in the Yellow Sea. Replica fields were calculated with BIO‐C‐SNAP, a C‐SNAP based normal mode model, which permits inclusion of bio‐absorption layers. The inversion was based on minimizing the rms difference, D, between measured and calculated values of TL at multiple source and receiver depths and ranges, and involved a simultaneous search for bio‐layer depth (d), bio‐layer thickness, bio‐alpha (a), geo‐sound speed, and geo‐alpha. The resultant values of D were extremely small (1.9 dB at 1.35 kHz). By contrast, inversion calculations, which assumed that all excess attenuation at this site was due to the bottom, resulted in unacceptably large values of D (9.5 dB at 1.35 kHz). The inverted value of d, 6.8 m, was consistent with laboratory measurements of the resonance frequencies of 10‐cm anchovies (1.35 kHz at 6 m), the dominant species...