针对水质监测的紫外-可见光谱双光程融合优化算法

An Optimized Ultraviolet-Visible Spectrum Dual Optical Path Length Fusion Algorithm for Water Quality Monitoring

紫外-可见光谱法多参数水质在线监测系统面对复杂水体时,常需要频繁改变探头光程以保持光谱较高的信噪比。然而,适合的光程往往需要大量实验才可确定,难以满足在线监测系统对实时性、精度、灵敏度、稳定性等的实际需求。研究了一种紫外-可见光谱双光程融合优化算法,将同时采集的长短两种光程光谱使用了滑窗法估计它们光谱噪声方差分布,确定光谱强噪声区间;由于长短光程光谱的信号强度不同,使用了遗传算法计算得到双光谱融合的最佳增益匹配倍率;最后,按噪声方差分布使用分段加权方式得到较高信噪比的双光程融合光谱。实验结果表明,利用该法对重庆长寿湖水样、嘉陵江某排污口及邻苯二甲酸氢钾标准溶液三种样本进行测试,其融合光谱在200~250 nm区域的强噪声得到抑制,零值干扰左推至220nm之前,样本的峰值信噪比均有显著提高,证明了算法的有效性和普适性。该算法无需大量实验以获得最佳光程,对于拓宽紫外-可见光谱水质在线监测系统的应用范围具有较为重要的现实意义。

In terms of water quality monitoring based on the ultraviolet-visible spectroscopy,different optical path lengths of spectrometer probe need to be set to maintain higher signal-to-noise ratio of the spectra when the water body measured is complex and changeable.However,large numbers of experiments always have to be undertaken to get the appropriate optical path length,which is difficult to meet the demand of real-time,accurate,sensitive and stable online monitoring system.In this paper,an optimized spectra fusion algorithm was developed to improve the signal-to-noise ratio of fused spectra from two independent spectra that were acquired using two different optical path lengths.In the fusion algorithm,the sliding-pane method was applied to obtain the distribution of noise variance of the spectra,so the region of strong noise in the spectra could be determined.Due to different signal intensity of spectra with long and short optical path length,genetic algorithm was used to calculate the optimal gain matching rate of fusion.Finally,according to the distribution of noise variance,piecewise weighted method is applied to achieve a fusion spectrum with higher signal-to-noise ratio.The experimental results showed that the fusion algorithm could effectively enhance the signal-to-noise ratio of the fused spectra for each sample without altering the optical path lengths the noise within 200~250 nm was suppressed and the low-noise and high-sensitivity spectra in the visible band were preserved;Zero interference was moved to the left of 220 nm of the spectrum.This means the fusion algorithm not only shows improvements in both signal-to-noise ratio and the detailed characteristics of the spectrum,but also reduces the excessive number of experiments in order to optimize optical path length and minimize noise in spectra.It has important practical significance to broaden the application range of the ultraviolet-visible spectroscopy based water quality monitoring system.