## 1 Introduction  
The transportation of natural sediments from upland areas to coastal waters generally occurs through rivers. These sediments have significant implications for the coastal ecological environment, coastal disaster prevention, coastal structure management, and coastal sedimentation [1; 2; 3]. Additionally, the interaction between flow and sedimentation plays a crucial role in the occurrence of scour, which is a prominent hazard and engineering problem for various coastal and river structures [4]. Furthermore, the confluence estuarine zone experiences widespread sediment deposition, leading to the formation of expansive deltaic regions where the riverine and marine environments intersect. However, this process also introduces challenges such as ecosystem stability and increased flooding [5]. Most of the sediment is transported as suspended particles, and the quantity supplied varies over time [6; 7; 8]. It should be noted that not all transported sediments reach the ocean due to factors such as the large distance and absence of water flow. Maximum transport occurs during flood periods [9]. For instance, in the southeastern Yellow Sea, which lies between China and the Korean Peninsula, the surface concentrations of suspended sediments range from 5 to 100 mg/L, while the bottom concentrations range from 5 to 500 mg/L [10]. This variability is attributed to the late onset of monsoon winds, which allows the sediment generated and transported from rivers during summer rainy seasons to remain stratified [10]. Furthermore, the Yellow Sea is influenced by suspended sediment transported from the Yellow River in China, with an average concentration of approximately 200-1300 mg/L at the river mouth [11; 12]. Therefore, the effective management of suspended sediments is vital for addressing erosion, sediment-related problems, and braiding phenomena in estuaries and coastal areas. Accurate identification and interpretation of suspended-sediment concentrations that are transported from rivers to the ocean play a critical role in achieving this management objective. While numerical analysis methods are commonly employed to quantify suspended sediment, their reliability is compromised due to the complex dynamics involving tide, wave action, flow mixing, sediment clumping, sinking, and resuspension [13; 14; 15]. Consequently, measurements offer the most precise means of determining the amount of sediment spread and the amount that is transported from rivers to the coast. Several studies have proposed various indirect and direct methods to estimate the concentrations of suspended sediments in estuaries and coastal areas [16; 17]. Among these, the direct methods of suspended-sediment concentration measurements involve trap, bottle, pump, and acoustic sampling methods [16]. However, traditional measurement methods such as trap and bottle methods require a significant amount of time and resources and are usually technically difficult. Additionally, they cannot continuously measure sediment concentration. Moreover, when using acoustic profiler equipment, observations are possible only within a limited range of particle diameters. Another disadvantage is that measurements in the presence of bubbles are often difficult [18]. In addition to these, measurement methods using laser diffraction, conductivity, and radiation techniques have been presented; however, these techniques also present evident economic and technical limitations. Owing to these difficulties, various indirect measurement methods have been developed to estimate the concentrations of suspended sand in estuaries and coastal areas. For image-based concentration estimation methods using remote sensing, effective monitoring of the dynamic changes in sediment and suspended matter is feasible. However, such monitoring is possible only in the presence of actually measured floating-matter data, and the efficiency is speculated to be low due to the limited data size.