## 1 Introduction  
Data on coastal topography and offshore areas are crucial for interpreting spatial and temporal changes. In particular, the importance of coastal topography and offshore data has been recognized in the modern society with the development of the marine industries. The construction of large-scale artificial structures for dredging and landfilling in offshore areas alters the natural topography, leading to changes in water flow patterns, magnitude, wave characteristics, and other related factors. Such changes in hydraulic mechanics result in variations in sedimentation, causing alterations in the existing topography and substrates [1, 2]. Estuarine areas possess particularly complex hydraulic characteristics, and artificial structures alter these hydraulic properties, leading to multifaceted changes in topographical features. In addition, estuarine areas are where seawater and freshwater mix, and considerable amounts of sediment, transported from upstream, are deposited as the water depth and velocity decrease, leading to the development of numerous sandbars, both large and small, parallel to the shoreline [3, 4, 5]. Shorelines are directly affected by the relationship between the discharge of suspended sediment and the flow rate of a river estuary. Monitoring changes in the shoreline is essential to conserve ecosystems, and the preservation of marine ecosystems is necessary for maintaining human livelihoods. The estuary of the Nakdong River, in the southeast of Republic of Korea, has undergone important artificial environmental changes since the 1980s. These include the development of industrial complexes, the construction of levees along the river, and the development of the surrounding areas, such as the establishment of residential areas through landfill and the construction of the New Port. Recently, as a part of a large-scale smart city industrial project, a scheme to create an international eco-friendly cultural city in this region is underway, making it an even more crucial area in terms of its transformation. The Nakdong River estuary has undergone considerable changes in terms of its topography owing to frequent industrial and residential development, including the construction of artificial structures and large-scale projects that affect the mixing of fresh- and saltwater [6]. Additionally, the construction of the estuary embankment has altered the pattern of intermittent mixing between the freshwater and saltwater, causing continuous sedimentation near previously formed islands owing to a loss of momentum toward the open sea [6]. Topographical changes, in both seafloor topography and sandbar formation, are occurring extensively throughout the estuarine region [7; 8; 9; 10; 11]. Currently, the estuarine area of the Nakdong River is a subject of research in various fields owing to its social and environmental importance. [PERSON] et al. [12] explored the characteristics of changes in the downstream oceanic physical environment depending on the opening and closing of the Nakdong River estuarine dike. [PERSON] and [PERSON] [13] studied the discharge tendencies of the outflow water according to the structural shape of the estuary dam to examine the tendency of geomorphic changes in the southern part of the estuary. [PERSON] et al. [14] studied the topographical changes on Jinwoo and Shinja Islands in the Nakdong River estuary from 2007 to 2012. [PERSON] et al. [15] analyzed changes in the seafloor topography in the southern part of Jinwoo Island, comparing the results with the effects of typhoons. Recently, aerial photographs and satellite images have been actively analyzed. For example, [PERSON] et al. [16] analyzed the coastal erosion rate of the sandbar area using aerial surveys, and [PERSON] et al. [17] analyzed the coastal erosion rate of the sandbars in the Nakdong River estuary using aerial photographs and SPOT-5 satellite images. [PERSON] et al. [18] monitored changes in the river mouth and tidal flat using a video monitoring system for Doyo sandbar. Additionally, [PERSON] et al.