The Acoustical properties of the sea bottom can be described with a geoacoustic (GA) model comprising several layers characterized by the parameters such as sound speed, density, sound absorption and thickness. As the parameters are difficult to measure directly, they are often estimated by inversion methods. Although GA inversion is the most economical method to infer the seabed acoustical parameter values, the results are unsatisfactory owing to the ambiguities between GA parameter values obtained in this way.

Researchers from the Institute of Acoustics of the Chinese Academic of Sciences (IACAS) proposed that model-free parameters (P, Q) could describe the reflection characteristics of the bottom. They also demonstrated that the values of P and Q were consistent with the GA parameter values inverted from different models.

Researchers inverted data from a previous acoustic propagation experiment for the seabed GA parameter values. At the frequency band of 140-180 Hz and 225-280 Hz, the values of P and Q corresponding to two GA model assumptions were listed in figure 2. The inverted results showed the consistency between the inverted GA parameter values in different bottom structure assumptions and reflection coefficients described by (P, Q) parameters.

The parameters (P, Q) provide a simple representation of the seabed characteristics, and could be used as a basis for research focused on sea bottom reflective characteristics, classification of sea bottom, and fast-field computation.

Figure 1. Amplitude and phase of the reflective coefficient of the real SACLANT bottom and its Effective Half Space at the frequency of 500 Hz (for grazing angle less than 15°). (Image by IACAS)

Figure 2. Performance of PQ in frequency band 140–180 Hz (LFM1) and 225–280 Hz (LFM2). (Image by IACAS)

The research, published in IEEE Journal of Oceanic Engineering, was supported by the National Natural Science Foundation of China under Grant11774375 and 11804360.

Reference:

ZHANG Chaojin, WU Jinrong, MO Yaxiao, SUN Bingwen, MA Li. The Same Reflective Characteristics for Different Effective Geoacoustic Parameters in Different Models. IEEE Journal of Oceanic Engineering, 2020. DOI: 10.1109/JOE.2020.2984295.

Contact:

ZHOU Wenjia

Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China

E-mail: media@mail.ioa.ac.cn