ESA-MDN: An Ensemble Self-Attention Enhanced Mixture Density Framework for UAV Multispectral Water Quality Parameter Retrieval

Highlights: What are the main findings? An ESA-MDN model is proposed to achieve high-precision modeling of the probability distribution of water quality parameters. Data augmentation is accomplished by leveraging the relationship between “multi-point sampling mean and multi-pixel reflectance”, thereby resolving the issue of insufficient sample size. What is the implication of the main finding? ESA-MDN effectively extracts water quality parameters from multispectral data, enabling the generation of spatiotemporal maps critical for identifying pollution sources and guiding emergency responses. Data augmentation can effectively increase the sample size, thereby providing more possibilities for improving model accuracy. Urban rivers, as crucial components of ecosystems, serve multiple functions, including flood control, drainage, and landscape services. However, with the acceleration of urbanization, factors such as industrial wastewater discharge, domestic sewage leakage, and surface runoff pollution have led to increasingly severe degradation of water quality in urban rivers. Unmanned aerial vehicle (UAV) remote sensing technology, with its sub-meter spatial resolution and operational flexibility, demonstrates significant advantages in the detailed monitoring of complex urban water systems. This study proposes an Ensemble Self-Attention Enhanced Mixture Density Network (ESA-MDN), which integrate an ensemble learning framework with a mixture density network and incorporates a self-attention mechanism for feature enhancement. This approach better captures the nonlinear relationships between water quality parameters and remote sensing features, achieving high-precision modeling of water quality parameter distributions. The resulting spatiotemporal distribution maps provide valuable support for pollution source identification and management decision making. The model successfully retrieved five water quality parameters, Chl-a, TSS, COD, TP, and DO, and validation metrics such as R², RMSE, MAE, MSE, MAPE, bias, and slope were utilized. Key metrics for the ESA-MDN test set were as follows: Chl-a (R² = 0.98, RMSE = 0.31), TSS (R² = 0.93, RMSE = 0.27), COD (R² = 0.93, RMSE = 0.39), TP (R² = 0.99, RMSE = 0.02), and DO (R² = 0.88, RMSE = 0.1). The results indicated that ESA-MDN can effectively extract water quality parameters from multispectral remote sensing data, with the generated spatiotemporal water quality distribution maps providing crucial support for pollution source identification and emergency response decision making.