基于透射光谱的水体含沙量在线监测技术研究

水体含沙量监测一直是水文观测及水中建设施工的重要观测内容，实时有效地监测水体含沙量具有重要实际价值。传统人工测量方法效率低下，无法实时监测，基于超声波等仪器监测方法虽可实现水体含沙量的实时测量，但在安全性、稳定性和测量范围上各有缺点。而基于光谱法进行物质含量监测的技术具有快速、无损、精确高效等优点，近年来被广泛应用于各领域，为水体含沙量在线监测技术提供新的思路与方法。但直接透射光谱法易受光源的不稳定和外界的杂散光的干扰，产生光谱噪声，同时由于仪器设备的光强饱和度，其测量量程存在限制。基于此，重点研究直接透射光谱噪声处理和多段标定技术，设计了一种基于透射光谱的水体含沙量快速大量程在线监测系统。首先基于朗伯-比尔基本定律理论分析水体含沙量与透射光强度之间的关系，然后利用比色皿支架实验室搭建了水体含沙量监测试验系统，配制不同含沙比例的标准溶液，进行强度-含沙量实际相关度标定测试。为克服光谱噪声影响，采用小波阈值去噪算法对原始透射光谱进行预处理，使用sym7小波基，极小极大阈值选择规则和7次小波分解次数，消除光谱噪声；设置不同积分时长，采用多段标定的方式实现了从4%到22%含沙量的大量程测量，并在算法中实现标定函数与测量量程自动匹配。结果表明标定曲线R平方值均在0.99以上，线性度良好，与理论相符合。最后对设计的水体含沙量在线监测系统进行实际精度测试，结果表明在大量程测量范围的测量误差均控制在0.4%以下，全量程误差均值为0.173%，误差标准差为0.115%，可满足工程实际需求。因此提出一种大量程的水体含沙量在线监测系统，并试验验证了系统测量准确度，可以用于水体含沙量实时在线监测。

Research on On-Line Monitoring Technology of Water Sediment Concentration Based on Transmission Spectrum

Monitoring water sediment concentration has always been important in hydrological observation and water construction. Real-time and effective monitoring of water sediment concentration has important practical value. Traditional manual measurement methods are inefficient and unable to monitor in real-time. Although instrument monitoring methods based on an ultrasonic wave can realize the real-time measurement of sediment concentration in a water body, they have disadvantages in terms of safety, stability and measuring range. The technology of material content monitoring based on spectroscopy is fast, non-destructive, accurate and efficient and has been widely used in various fields in recent years, providing new ideas and methods for on-line monitoring of water sediment content. However, direct transmission spectroscopy is susceptible to the instability of the light source and the interference of stray light from outside, resulting in spectral noise. At the same time, due to the light intensity saturation of the instrument and equipment, its measuring range is limited. Based on this, this paper focuses on direct transmission spectrum noise processing and multi-section calibration technology and designs a fast and large-range on-line monitoring system for water-sediment content based on transmission spectrum. First, the relationship between sediment content and transmitted light intensity in a water body is analyzed based on Lambert-Bill’s basic law theory. Then, a sediment monitoring test system for a water body is established by using colorimetric dish holder laboratory, and standard solutions with different sediment content ratios are prepared to calibrate the actual correlation degree of intensity-sediment content. In order to overcome the influence of spectral noise, the original transmission spectrum is pre-processed by a wavelet threshold denoising algorithm. Spectral noise is eliminated using sym7 wavelet base, minimum and maximum threshold selection rule and 7 times of wavelet decomposition. With different integration times, a large range measurement of sediment content from 4% to 22% is realized by multi-section calibration, and the calibration function and measurement range are automatically matched in the algorithm. The results show that the R-square values of the calibration curves are all above 0.99, with good linearity and by the theory. Finally, the on-line monitoring system for water-sediment content is designed and tested for actual accuracy. The results show that the measurement errors are all controlled below 0.4% in the wide range of measurement, the mean of full range error is 0.173%, and the standard deviation of error is 0.115%, which can meet the actual requirements of the project. Therefore, an on-line monitoring system for water-sediment concentration over a wide range is proposed in this paper, and the system’s measurement accuracy is verified by tests, which can be used for real-time on-line monitoring of water sediment concentration.