对基于彩虹现象的光学颗粒测量进行研究,提出了一种新的参数反演模型和算法,可同时测量颗粒的粒径和折射率。新算法基于经验模态分解的去噪技术,并采用一种特征点提取技术和基于Debye理论的反演最优点搜索算法,能较精确的迅速找到反演最优点。数值模拟结果表明,当信噪比降至5 dB时,直径反演最大误差小于10％,折射率反演最大误差小于0.1％。对不同温度下自由下落的水滴进行实验研究,水滴由波长532 nm功率14 mW的连续激光源照射, 产生的彩虹光线经大口径透镜收集,被位于透镜焦平面的CCD相机接收。实验结果同样表明此测量方法具有较好的精度和可靠性。

The parameter inverse problem of rainbow measurement was studied. The mathematic model was built and a novel inverse algorithm was presented which could simultaneously measure particle size and refractive index. The new algorithm removes noise using the technique based on empirical mode decomposition (EMD). A feature point extraction technique was presented and an optimal point search algorithm based on Debye theory was proposed which can rapidly find the relatively exact inversion parameter. Simulation results show that when the signal-to-noise ratio (SNR) drops to 5 dB, the maximum inversion error of diameter is less than 10％ and error of refractive index is less than 0.1％. A laboratory experiment was also taken which concentrated on detection of a rainbow formed by a free-falling raindrop at different temperature. The droplet was illuminated by a continuum laser with the wavelength of 532 nm and power of 14 mW. The rainbow light formed by the droplet was collected by a lens with large diameter and received by a linear CCD placed in the focus of the lens. The experimental results also show that the method is feasible and has a relatively good precision.