## 1 Introduction  
Various types of problems occur during sediment generation, transportation, and deposition. In particular, sediments cause serious problems in river maintenance, such as changes in the riverbed, water pollution, and a direct influence on the functions of hydraulic facilities [1, 2]. Therefore, it is extremely important to quantitatively identify and predict the amount of sediment in order to realize eco-friendly and sustainable river development [3, 4, 5, 6, 7, 8, 9]. In South Korea, the sediment-related problems occur locally on a relatively small-scale, and most of the sediment is transported in the form of suspended matter during the flood season, unlike the continental regions [6, 10]. Therefore, data on the amount of sediment that is measured at multiple points are required. However, it is challenging to add additional measurement points owing to economic reasons. In addition, sediment measurement during the flood season is extremely difficult, dangerous, and requires considerable manpower and time because of high flow velocities, thereby necessitating the introduction of a novel measurement method. Theoretically, the total amount of sediment that is transported in a river is the total quantity of the sediment that passes through the cross section of the river, and it is generally measured via different methods by categorization into the suspended sediment and bed load [11]. The suspended sediment is measured using mechanical samplers, such as depth-integrating samplers (D-74) and point-integrating samplers (P-61), and bottle samplers are mainly used for water sampling. When discrete interval sampling is used for water sampling, the discontinuous measurements and high sampling cost hinder the capture of the dynamic processes of sediment transport, deposition, and resuspension under field conditions. To overcome these shortcomings, devices that are capable of on-site real-time measurements have been developed for suspended sediment concentration (SSC) monitoring [12; 13]. The laser diffraction method can solve this time resolution problem, and many studies have been actively conducted since the late 1990s to analyze its applicability and validity [14]. [PERSON] [15] evaluated the applicability of the acoustic backscatter system and optical laser diffraction instrument (LISST) for suspended sediment measurement through laboratory experiments. In addition, [PERSON] et al. [16] reported that the SSC and particle size distribution can be accurately measured within the measurement range of LISST, thus indicating the applicability of LISST for laboratory experiments and research in rivers. [PERSON] et al. [17] performed laboratory experiments using natural sediment to compare the measurement results of LISST with the results of sieving, filtration, and weighting techniques that are conventional suspended sediment analysis methods. They verified that LISST presents the accurate particle size distribution of sediment. The accuracy and validity of the equipment have been verified through various studies. However, economic and technical problems are still encountered during field application. There is a growing interest in the newly applied methods for the prediction of suspended sediment and understanding sediment characteristics from image analysis. In recent years, an increasing number of studies have been conducted to measure the SSC and analyze the characteristics of sediment using images. [PERSON] et al. [18] proposed a suspended sediment monitoring method that estimates the turbidity of suspended sediment using the machine-learning-based analysis of the images captured from the water surface and employs the turbidity-concentration relationship. Nonetheless, for images capturing the water surface in air, the technologies for signal separation and division need to be improved because the signals that are reflected from the water surface, water body, and bottom are mixed, and an accurate analysis is difficult because the reflection tendency varies depending on the riverbed material.