## 1 Introduction  
At present, spectroscopic detection technology is widely used in all walks of life, such as medicine and health [1, 2], public safety [3, 4], food safety [5], environmental monitoring [6, 7, 8], and so on. When a spectrum is used to detect chemical oxygen demand (COD), the quality of spectral data is crucial, as this is closely related to the accuracy of the COD prediction model. At the same time, different detection environments can also have a significant impact on the detection results [9, 10, 11, 12, 13]. COD detection based on the spectral method is the result of multiple environmental factors working together. Therefore, the question of how to eliminate environmental interference and extract effective spectral features is the key to improving the accuracy of spectral detection [14]. Environmental factors mainly include pH, temperature, conductivity, etc. Because UV-Vis spectroscopy belongs to the electronic energy spectrum. The acidity or alkalinity (pH) of a solution can affect the absorption peak position and absorption coefficient of the spectrum [15]. Temperature changes can alter the energy emission of electrons, thereby changing the waveform of the spectrum. Conductivity is mainly composed of soluble inorganic salt ions, some of which have strong absorption in the ultraviolet band. Therefore, addressing the influence of these environmental factors is one of the important ways that the accuracy of COD detection by spectroscopic methods can be improved [16]. Changes in environmental factors (pH, temperature, and conductivity) cause certain interference to the spectrum when detecting COD in water with UV-Vis spectroscopy. This leads to the deviation of spectral data and influences the accuracy of COD detection. The influence of the environment on the detection of water parameters using spectroscopy methods has been researched, and corresponding compensation methods have also been proposed in some research. [PERSON] researched the relationship between COD and UV absorbance at 260 nm in the natural water of five rivers in Japan. He measured the absorbance of different inorganic salt ions in the water, indicating that inorganic salt ions have an influence on the spectroscopic detection of COD [17]. [PERSON] used UV-Vis spectroscopy to detect nitrite and nitrate in the samples. It indicated that nitrite and nitrate have absorption in UV-Vis spectroscopy and can influence the absorption spectrum of COD [18]. [PERSON] et al. researched the effects of various environmental factors on the detection of COD in water by UV spectroscopy through standard solutions and real water samples. The influencing mechanism was analyzed, and relevant conclusions were drawn [19]. The influence of environmental factors on the full spectrum is quite complex. From a holistic perspective, it is not possible to simply fit the variation in absorbance with environmental factors at each wavelength using a single rule or curve. With the research on data fusion technology and its effectiveness in related fields, considering the fusing of different environmental factors with UV-Vis spectral data can achieve comprehensive compensation for the influence of environmental factors. Thus, the accuracy of COD detection based on UV-Vis spectroscopy is improved. The water quality analysis methods of chemometrics have a development history of more than 50 years. However, the research method of combining spectroscopy with other forms of sensor data fusion has only been applied in recent years. It has problems such as poor robustness and low analysis accuracy [20]. Multi-source information fusion has its own characteristics and analysis methods when the data source to be fused includes spectral data [21]. According to different data sources, spectral fusion can be divided into two categories: the first is the fusion of different spectra, and the second is the fusion of spectra with other sensor data [22; 23; 24]. This research belongs to the second case. The fusion of spectroscopy with other sensors has been applied in many aspects.