A hybrid water quality prediction model based on variational mode decomposition and bidirectional gated recursive unit

Abstract

Water quality predicted accuracy is beneficial to river ecological management and water pollution prevention. Owing to water quality data has the characteristics of nonlinearity and instability, it is difficult to predict the change of water quality. This paper proposes a hybrid water quality prediction model based on variational mode decomposition optimized by the sparrow search algorithm (SSA-VMD) and bidirectional gated recursive unit (BiGRU). First, the sparrow search algorithm selects fuzzy entropy (FE) as the fitness function to optimize the two parameters of VMD, which improves the adaptability of VMD. Second, SSA-VMD is used to decompose the original data into several components with different center frequencies. Finally, BiGRU is employed to predict each component separately, which significantly improves predicted accuracy. The proposed model is validated using data about dissolved oxygen (DO) and the potential of hydrogen (pH) from the Xiaojinshan Monitoring Station in Qiandao Lake, Hangzhou, China. The experimental results show that the proposed model has superior prediction accuracy and stability when compared with other models, such as EMD-based models and other CEEMDAN-based models. The prediction accuracy of DO can reach 97.8% and pH is 96.1%. Therefore, the proposed model can provide technical support for river water quality protection and pollution prevention. HIGHLIGHTS In order to overcome the problem of nonlinear instability of water quality data, an adaptive decomposition method of improved VMD by SSA is proposed. In the optimization process, fuzzy entropy (FE) is selected as the fitness function to evaluate the complexity between orders.; In order to fully explore the time characteristics of water quality, the BiGRU neural network is used as the prediction model.; The proposed model is applied to the prediction of DO and pH in real rivers.;

Keywords

• bidirectional gated recursive unit
• sparrow search algorithm
• variational modal decomposition
• water quality prediction