Identification of Surface Sedimentary Microstructures of Tidal Flat Extracted from Ultra-high Resolution UAV Data

Abstract

The surface sedimentary structures are formed by tidal currents in a tidal flat where actively occurs sediment erosion and deposition. In general, since the sedimentary structure of a tidal flat is determined by particle size and flow velocity, it is highly correlated with the sedimentary environment such as sedimentary facies, sediment particle size, and macroinvertebrate burrows. Therefore, it is very important to grasp the sedimentary structure in a wide area to analyze the sedimentary environment of tidal flats. In previous studies, remote sensing image that can collect in a wide area has been used to analyze the surface sedimentary structures. Among the sedimentary structures, it is necessary to utilize ultra-highresolution unmanned aerial vehicles (UAV) images in millimeter units to analyze surface sedimentary microstructures such as ripple marks of micro scales and mud cracks. However, a study of analysis of the correlation between the surface sedimentary microstructures and the sedimentary environment has never been conducted using ultra-high resolution UAV images. The objective of this study is to extract surface sedimentary microstructures such as mud cracks and ripple marks and to analyze their relationship with the sedimentary environment. A case study is performed using ultra-high resolution UAV images with 9 mm spatial resolution and RGB channel acquired on May 2022 in Korean Tidal Flat. Mud crack and ripple marks appear as dark pixels in UAV images due to the shadows created by the underwater shrinkage of muddy sediment and slope, respectively. Therefore, the convolutional filter, which is one of the image enhancement techniques, was applied to extract the line structure of mud crack and ripple marks from UAV images. The correlation between individual surface sedimentary microstructures and sedimentary environment such as sedimentary facies and terrain elevation was then analyzed using field survey data. As a result of the analysis, mud cracks and ripples were highly correlated with terrain elevation and sedimentary facies. Therefore, it is expected that it can be used as basic data for classification of sedimentary facies and analysis of sediment particle size through establishing of spatial data of surface sedimentary microstructures from UAV images.