基于激光外差干涉技术的中频水声声压复现研究

In underwater acoustic metrology, the primary standard for underwater acoustic pressure is the source for quantity traceability and dissemination. The accuracy of acoustic pressure is directly related to the performance characteristics of underwater acoustic devices and also the development state of oceanic acoustic techniques. As a non-invasive measurement, optical method, which has been identified as the main technique for the next generation of primary underwater acoustic standard by CIPM, is more advantageous than the traditional reciprocity method. To solve some key problems currently existing in the unit realization of underwater acoustic pressure, 1) the project aims at achieving the unit realization of underwater acoustic pressure directly and accurately by measuring the acoustic particle velocity via laser heterodyne interferometry. A thin pellicle strip, which faithfully follows the motion of the propagating acoustic field, is placed in the water to reflect the optical beam. 2) Moreover, this project focuses on the investigations of systematic effects which would contribute to the overall measurement uncertainty. These systematic effects mainly include acousto-optic effect, pellicle vibration modes, pellicle transmission loss and alignment errors. Related correction methods are proposed as well to improve the accuracy of unit realization of pressure. 3) A custom-made heterodyne interferometer with high stability is used, and a corresponding demodulation algorithm for particle velocity with good robustness to low-frequency vibration is proposed in this project. 4) A full uncertainty budget is given with each part of the system properly evaluated. The final goal of this project is to establish a laser heterodyne interferometry-based primary standard for underwater acoustic pressure in the frequency range 10 kHz to 500 kHz, which could achieve primary calibration of hydrophones with the uncertainty being less than 0.5 dB (k=2).

水声声压基准是水声计量中量值溯源和传递体系的源头，量值的准确与否直接关系到水声设备的性能和质量、海洋声学技术的发展水平。作为非侵入式测量，光学法相比传统的互易法优势显著，被国际计量委员会认定为下一代水声基准的主要技术。针对当前水声声压复现存在的一些关键问题，本项目：1)利用反光透声薄膜反映水质点随声波振动，研究激光外差干涉技术测量声质点的振动速度，实现对水下声压量值的直接、准确复现；2)重点探讨声压复现中声光效应、薄膜振动模态、薄膜传输损失、对准误差等系统效应的影响机理及修正方法，提高声压复现的精度；3)采用自主研制的高稳定度激光外差干涉系统，提出具有抗低频干扰能力的质点振动速度解调算法；4)完整评估系统各部分的测量不确定度，最终建立基于激光外差干涉技术的中频（10kHz-500kHz）水声声压基准装置，实现对水听器声压灵敏度的原级校准，不确定度优于0.5dB(k=2)。

激光干涉测量是新一代水声计量基准的主要技术。项目围绕激光干涉法水下声压量值复现与水听器原级校准，开展了高稳定度激光外差干涉测量系统研制、水质点振速测量与信号解调、系统效应分析与修正、测量不确定度评估等系列研究。利用自主研制的激光干涉系统测量水下声场引起的带状薄膜振动，设计过零点解调算法得到多普勒频移及振速信号，实现对水下声压量值的准确复现及水听器校准；仿真分析并实验测量了不同形态薄膜与水质点振动的跟随性，确定了适合项目频段的最佳薄膜方案；研究了薄膜传输损失、水下声光效应、对准误差等系统效应对声压复现的影响，给出了完整的测量不确定度评估方案。.项目的主要研究成果是建立了激光外差干涉法水声声压复现装置，能够在10 kHz ~ 500 kHz频率范围实现对水听器的原级校准，测量不确定度优于0.5 dB (k=2)。与当前的互易法国家水声基准进行了比对，校准结果等效且不确定度更小，具备了申请激光干涉法国家水声计量基准的条件，为实现水声精密测量和水声声压量值的扁平化传递奠定了良好基础。