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浙江大学学报(工学版)
Journal of ZheJiang University (Engineering Science)  2020, Vol. 54 Issue (5): 972-977    DOI: 10.3785/j.issn.1008-973X.2020.05.015
Earth Science     
Application of broadband parametric array in sub-bottom profile measurement
Han-yun ZHOU(),Shan-he HUANG*()
Ocean College, Zhejiang University, Zhoushan 316022, China
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Abstract  

A system design of a parametric array sub-bottom profiler was proposed to improve the detection accuracy of the broadband parametric array. Transducer array is used as the acoustic emission device, which can significantly improve the directivity of the sound and effectively suppress side lobes compared with a single transducer. The waveform and spectrum changes of the linear frequency modulation (LFM) signals before and after demodulation were compared and analyzed based on the nonlinear self-demodulation model of the parametric array. The bandwidth of the self-demodulated signal was doubled relative to its original value, and the amplitude of the high-frequency component was higher than that of the low-frequency component, which basically accorded with the growth trend of 12 dB per octave. Based on this, an improved matched filter was designed to perform pulse compression, and the spectrum correction method was introduced to countervail spectrum change. Simulation shows that the transducer array has high directivity and ensures the high directivity of the self-demodulated signal due to the fact that the self-demodulated signal has the same directivity with the primary frequency signal. The improved pulse compression technique can further improve the detection resolution by selecting appropriate bandwidth of LFM signal. The resolution is up to 7.5 cm, enabling high-precision sub-bottom profile measurement.

Key words： broadband parametric array      sub-bottom profile measurement      directivity      linear frequency modulation signal      pulse compression     
Received: 19 April 2019      Published: 05 May 2020
CLC:  TB 566  
Corresponding Authors: Shan-he HUANG     E-mail: 11634017@zju.edu.cn;davidhuang@zju.edu.cn
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Han-yun ZHOU
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Cite this article:

Han-yun ZHOU,Shan-he HUANG. Application of broadband parametric array in sub-bottom profile measurement. Journal of ZheJiang University (Engineering Science), 2020, 54(5): 972-977.

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http://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2020.05.015     OR     http://www.zjujournals.com/eng/Y2020/V54/I5/972


宽带参量阵在浅地层剖面测量中的应用

为了提高宽带参量阵的探测精度，提出参量阵浅地层剖面仪的系统设计. 以换能器阵列作为声发射装置，相较单个换能器能显著提高声源的指向性，有效抑制旁瓣. 利用参量阵的非线性自解调模型，对比分析线性调频信号自解调前、后的波形与频谱变化，分析得出自解调信号的频宽扩展为原信号的2倍，且带宽内信号幅值满足每倍频程12 dB的增长态势. 据此设计改进匹配滤波器来进行脉冲压缩，并通过频谱修正来抑制频谱变化. 仿真结果表明，该宽带参量阵的换能器阵列具有较好的指向性，根据自解调信号和原频信号同指向性的原理，保证自解调信号的高指向性. 提出的改进脉冲压缩技术能进一步提高探测分辨率，通过选择合适的调频范围，距离分辨率可以达到7.5 cm，可以实现高精度的海底地层探测.


关键词： 宽带参量阵,  地层探测,  指向性,  线性调频信号,  脉冲压缩 
Fig.1 System configuration of parametric array sub-bottom profiler
Fig.2 Directivity of transducer element
Fig.3 Directivity of 5×5 transducer array
Fig.4 Comparison of LFM and PALFM in time domain
Fig.5 Comparison of LFM and PALFM in frequency domain
Fig.6 Pulse compression output of ordinary matched filter
Fig.7 Comparison of pulse compression outputs of ordinary matched filter and modified matched filter
Fig.8 Spectrum comparison before and after spectrum correction
Fig.9 Pulse compression output for PALFM after spectral correction
Fig.10 Simulated echo signal
Fig.11 Sub-bottom profile measurement with modified matched filter
Fig.12 Cross-correlation result of PALFM and echo signal
Fig.13 Comparison of pulse compression outputs of PALFM with different bandwidths
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