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Research on Optimization Method of Signal-to-Noise Ratio in Optical Measurement Systems
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摘要: 在光学测量中常常受低信噪比问题的影响，导致测量结果的不确定度增大。近红外波段双向反射分布函数（BRDF）的测量由于红外信号强度偏弱，易受环境干扰，面临的低信噪比问题尤其突出。光学测量系统的信噪比问题一般产生自探测系统，对于红外测量系统来说，经常使用斩波器、锁相放大器进行弱信号测量，但同时也引入了噪声问题。因此，本文针对近红外波段BRDF测量信噪比问题，从探测器、斩波器、锁相放大器三部分着手，分析噪声来源并针对性地提出抑制方法与优化措施，以提升信号信噪比。优化后的测量系统较优化前抗噪声能力提高，可重复性由优化前的2.1%提升到1.6%。Abstract: Optical measurement are often affected by low signal-to-noise ratios (SNR), resulting in larger measurement uncertainty. Measurement of the bidirectional reflectance distribution function (BRDF) in the near-infrared is particularly vulnerable to environmental interference due to weak infrared signals. The signal-to-noise ratio problem of optical measurement systems generally arises from detection systems. For infrared measurement systems, choppers and lock-in amplifiers are often used for weak signal measurement, but noise problems are also introduced at the same time. Therefore, this article focuses on the SNR of BRDF measurement in the near-infrared, aiming at the detector, chopper and lock-in amplifier, analyzing the source of noise, and proposing suppression methods and optimization measures to improve the signal-to-noise ratio. The optimized measurement system has improved anti-noise ability compared with that before optimization, and the repeatability has been improved from 2.1% to 1.6%.
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图 4 优化前后测量结果比较
Figure 4. Comparison of measurement results before and after optimization
表 1 锁相放大器参数设定
Table 1. Lock-in amplifier parameters
参数类型 参数值 时间常数 1 s 灵敏度 100 mV（测量光源） 100 μV（测量漫反射） 存储模式 高噪声 同步 关 滤波器选择 24 dB/oct 参考频率 780 Hz 
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