Air pollution affects public health, destroys ecological environment and even aggravates climate change, and PM2.5 is an important factor causing pollution. Therefore, accurate and continuous spatiotemporal PM2.5 concentration inversion is of great significance for air pollution control. Nevertheless, current high temporal resolution inversions are predominantly conducted using Top-of-atmosphere reflectance, nighttime concentration inversion cannot be realized in the visible band. Moreover, existing hybrid models often rely on linear integrated, increasing the risk of overfitting. Therefore, we propose an improved stacking model that contains XGBoost and CatBoost model, stacked by elastic net regression. By fusing features from multi-source data and accounting for spatiotemporal heterogeneity, the model enables the simultaneous inversion of daytime and nighttime PM2.5 concentrations. Compared to using Top-of-atmosphere reflectance alone, the daytime inversion results demonstrate a 1.08% increase in R2 and a reduction of 1.34μg/m3 in RMSE. Meanwhile, the nighttime inversion results show a 2.04% improvement in R2 and reduce the MAE to 9.54μg/m3 when spatiotemporal features are used. Applying the model to the Beijing-Tianjin-Hebei region enables spatiotemporal continuous inversion of PM2.5 concentrations in the region.
This study investigated the spatial changes in reed distribution in Baiyangdian, using high-resolution remote sensing imagery. It revealed a substantial alteration in the distribution of reeds within Baiyangdian from 2016 to 2022. The reeds have converted with five types of land cover, including water, cropland, orchards, woodlands and building land. The reed area increased by 14.3% to 103.7 km2 in 2022 compared to 2016. The expansion primarily occurred in the shallow waters of Zaozhadian in the western part of Baiyangdian. The expansion of reed area is attributed to the continuous water replenishment in order to preserve the ecology and the restoration of cultivated land to wetland ecosystem. After the removal of the dyke, the 26.55 km2 of reed swamp on the dyke became open water. It increases the hydraulic connectivity of Baiyangdian lake and accelerates the restoration of ecological function of Baiyangdian Lake.
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