Research On The Seawater Quality Monitoring Technology Based On UV-visible Spectra

Monitoring seawater quality is a subject of growing importance around the worldbecause of the exploitation and utilization of marine resources. However, thetraditional seawater monitoring method requires many chemical reagents. It is easy toproduce secondary pollution and complicated to operate. The instruments can also bedifficult to achieve the real-time and on-line monitoring. So the paper researched onthe seawater monitoring technology based on the UV-Visible spectroscopy has greatsignificance.The paper reviewed the existing theory and modeling methods of UV-Visiblespectroscopy, such as single-wavelength method and dual-wavelength method. Thenthe full spectrum method based on the UV-Visible spectroscopy was proposed. Themethods method was partial least squares which was good at handling the multiplecorrelation problems with the multivariate. The experiments of potassium hydrogenphthalate solution in the artificial seawater show that this method is feasible. Thesingle dependent variable PLS model which was used to measure COD value has ahigh correlation coefficient of R2and low RMSEP. The Multivariate PLS model forCOD, TOC and TSS measurement also get a good result. There are two aspects of thedevelopment with the PLS calibration models, one is the nonlinearities in the signalsaturation, the other is dataset gradient. Two models were built up and gave therelevant conclusions. In the experiments of nitrate, different mathematical treatmentsfor spectra processing and different wavelength ranges were compared to determinethe best mode1. The best model is obtained with the original spectra of ultraviolet.Test of the model with an independent dataset exhibits a good agreement between thepredicted and observed values, with the correlation coefficient of0.977, and theprediction RMSEP is2.04μM/L.One kind of instrument was designed in this paper based on the UV-Visiblespectroscopy which can achieve real-time, in-situ and on-line monitoring. We choosexenon flash lamp as the illuminant, flat field and imaging concave grating andphotodiode array as the sensors. At the same time, the overall structure of theinstrument, optical system and buoy were also designed The experimental results show that the UV-Visible spectroscopy with the partialleast squares regression can predict the seawater parameters well. The design andresearch on the instrument will make an effective contribution to the development ofthe seawater monitoring technology.