Zhang Shiwen, Li Liyan, Liu Yuliang, Zhou Yan
Optoelectronics System Laboratory, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
College of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China.
Sensors (Basel). 2023 Oct 14;23(20):8460. doi: 10.3390/s23208460.
The refractive index measurement of seawater has proven significance in oceanography, while an optical heterodyne interferometer is an important, highly accurate, tool used for seawater refractive index measurement. However, for practical seawater refractive index measurement, the refractive index of seawater needs to be monitored for long periods of time, and the influence of drift error on the measurement results for these cases cannot be ignored. This paper proposes a drift error compensation algorithm based on wavelet decomposition, which can adaptively separate the background from the signal, and then calculate the frequency difference to compensate for the drift error. It is suitable for unstable signals, especially signals with large differences between the beginning and the end, which is common in actual seawater refractive index monitoring. The authors identify that the primary cause of drift error is the frequency instability of the acousto-optic frequency shifter (AOFS), and the actual frequency difference was measured through experimentation. The frequency difference was around 0.1 Hz. Simulation experiments were designed to verify the effectiveness of the algorithm, and the standard deviation of the optical length of the results was on the scale of 10 m. Liquid refractive index measurement experiments were carried out in a laboratory, and the measurement error was reduced from 36.942% to 0.592% after algorithm processing. Field experiments were carried out regarding seawater refractive index monitoring, and the algorithm-processing results are able to match the motion of the target vehicle. The experimental data were processed with different algorithms, and, according to the comparison of the results, the proposed algorithm performs better than other existing drift error elimination algorithms.
海水折射率测量在海洋学中已被证明具有重要意义，而光学外差干涉仪是用于海水折射率测量的一种重要且高精度的工具。然而，对于实际的海水折射率测量，需要长时间监测海水的折射率，并且在这些情况下漂移误差对测量结果的影响不可忽视。本文提出了一种基于小波分解的漂移误差补偿算法，该算法可以自适应地将背景与信号分离，然后计算频率差以补偿漂移误差。它适用于不稳定信号，特别是在实际海水折射率监测中常见的首尾差异较大的信号。作者确定漂移误差的主要原因是声光频移器（AOFS）的频率不稳定，并通过实验测量了实际频率差。频率差约为0.1 Hz。设计了模拟实验来验证该算法的有效性，结果的光程标准差在10 m量级。在实验室进行了液体折射率测量实验，算法处理后测量误差从36.942%降低到0.592%。针对海水折射率监测进行了现场实验，算法处理结果能够与目标车辆的运动相匹配。用不同算法对实验数据进行处理，根据结果比较，所提出的算法比其他现有的漂移误差消除算法表现更好。
