# Space-Ground Remote Sensor Network for Monitoring Suspended Sediments in the Yellow River Basin
## 3 Results and Analysis  
### Hyperspectral Monitoring of Water and Sediment in the Qingshui River  
The Qingshui River is a tributary on the right bank of the Yellow River, flowing through the Ningxia Hui Autonomous Region. The Qingshui River basin in Ningxia belongs to a temperate continental climate, with cold winters and hot summers, significant day-night temperature differences, and an area of approximately 16,000 square kilometers, with a water area of about 53,000 hectares, mainly including the Qingshui River itself and its tributaries, lakes, and other water bodies. It is an important part of the water resources in Ningxia and the Yellow River basin, with abundant natural resources and a unique ecological environment. The water resources of the Qingshui River basin supply local needs for agricultural irrigation, domestic water use, and industrial water use. The terrain of the Qingshui River basin in Ningxia is characterized by significant fluctuations, mainly mountainous and hilly areas with narrow river valleys. Precipitation is concentrated in the summer, often with intense rainfall, leading to flash floods [39]. As shown in Figure 3, high-resolution imagery can be used to monitor changes in land cover in the Qingshui River basin. The Normalized Difference Vegetation Index (NDVI) is an index used to reflect the degree of vegetation cover and growth conditions on the ground, with values ranging from \(-\)1 to 1. A higher value indicates better vegetation cover (Figure 4b). In the Qingshui River basin, the NDVI index can be used to analyze trends in vegetation changes, including vegetation cover, seasonal variations, and desertification levels, and to assess the erosion modulus of the basin soil [40]. By combining DEM (Figure 4a) and precipitation forecasts, the erosion status of the soil-water system at different times can be assessed [41], and the water volume and sediment concentration in the river can be predicted. Real measured data from 12 hydrological stations in the Loess Plateau region show that sediment concentrations can range from as low as 0.41 mg/L to as high as 1080 g/L; satellite remote sensing results indicate that, in the Yellow River channel affected by the Loess Plateau, the sediment concentration in summer and autumn reaches 2.998 g/L, while, in winter and spring, it decreases to as low as 1.126 g/L [26]. The Qingshui River basin is part of the Loess Plateau, and, as a tributary, its narrow river channel makes it difficult to accurately estimate sediment concentrations using satellite remote sensing data with a resolution of 30 m. In situ hyperspectral monitoring can be used to monitor sediment concentrations, as shown in conventional hydrological stations and the Wangtuan station in the Qingshui River basin, with sediment concentrations reaching as high as 732 g/L (Figure 4c,d). The spectral data recorded at this station not only reflect changes in sediment concentrations but also capture variations in organic matter such as algae in the Qingshui River, as shown in Figure 4c. As shown in Figure 5, during the period from 26 August 2022 to 26 September 2022, the daytime sediment concentration at the Wangtuan station can be monitored in real time through hyperspectral reflectance ratios, with a time resolution better than 10 min. The sediment concentration obtained through this non-contact hyperspectral real-time inversion is consistent with the synchronously measured sediment concentration obtained  
Figure 4: **(a)** DEM of the Qingshui River basin, (b) vegetation in the Qingshui River basin, (c,d) typical spectra of high-concentration sediment at the Wangtuan spectral station in the Qingshui River basin. Figure 3: High-resolution satellite remote sensing data for the upper reaches of the Yellow River in Ningxia: (**a**) Daily domestic high-resolution optical satellite from CRESDA, (**b–d**) vegetation changes in May, July, and October (vegetation areas are shown in red, clear water areas in dark color).