Correlation between the sedimentary facies and microstructures on tidal flats using high-resolution UAV data

Abstract

Tidal flat sedimentary structures play an important role in understanding the environment in which they were formed because their form is determined by tides and currents. They are classified into mega, macro, meso and micro-scale depending on the size. Remote sensing such as satellite images and aerial photographs used to observe the structures along with field surveys. However, traditional methods have difficulty in detecting micro-scale features such as ripple marks due to low spatial resolution. Therefore, there is a need to use high-resolution Unmanned Aerial Vehicles (UAV) that can be operated reasonably in spatiotemporal. However, there is a lack of research on analyzing micro-scale features using UAV. In this study, we performed a geometric analysis of ripple marks, which are microstructures, using ultra-high-resolution UAV, and analyzed the relationship with sedimentary environments such as surrounding topography and sedimentary facies. The study area is Hwang-do located on the west coast of Korea, and we used UAV images with RGB channels with a spatial resolution of about 0.9 mm. We used the Structure from Motion (SfM) tool to extract point clouds and create an orthoimage and Digital Elevation Model (DEM). We could visually identify ripple marks from both images and calculate ripple parameters. Ripple marks in the study area were formed in a silty sand environment with a grain size range of 3.5 φ – 4 φ in the high-altitude lower intertidal zone, and irregular ripples with an average wavelength and height of approximately 7 cm and 5 cm, respectively, were mainly observed. This study suggests that remote sensing can be used to efficiently observe microstructures rather than manual measurements. This can be used as basic data for tidal flat environment analysis such as improving sedimentary facies classification accuracy in the future.