Abstract
The west coast of South Korea is characterized by a wide macrotidal area with a maximum tidal range of ∼10 m. The sea surface elevation varies with the tidal phase, which leads to significant changes in the vertical structure of the physical, chemical, and biological properties of the water column, especially when the interaction by waves and/or the freshwater and sediment input from the river increases. Under such conditions, it is difficult to carry out continuous and consistent measurements of the vertical structures of the water qualities using a conventional observation system that is fixed to the seabed or sea surface because the thickness of the water column constantly changes. Based on the demand for long-term observations of the vertical structures of the water properties in macrotidal environments, the Intelligent Buoy System (INBUS) was developed by the Korea Institute of Ocean Science and Technology (KIOST). INBUS is a buoy equipped with an instrument frame, which is similar to other buoys that are fixed to the sea surface. During every measurement, INBUS detects the water depth and sends the frame down to the seabed to measure the water quality at every vertical level set up in the system. For example, if N levels are set in INBUS, the water depth of each measurement is divided by N layers and the instruments in the lifting frame measure the water properties of each of the N layers while they are descending to the bottom. Based on this procedure, the vertical structure of the water column is consistently measured in N layers regardless of changes of the water depth due to tides and waves. The lifting and measuring process is automatically controlled by INBUS once it is set up in the system. In addition, because INBUS allows bidirectional communication through code division multiple access (CDMA), the system can be controlled by stations on land. If the CDMA communication becomes inoperable owing to extreme wave conditions or the buoy is lost because of incidents such as a collision with a ship, the location of INBUS can be tracked by low-earth-orbit satellites.
Highlights
Coastal waters are interfaces between land and ocean and are important for human life because of their geographical proximity as well as their function as food, transportation, and recreation sources
One of the weaknesses of Intelligent Buoy System (INBUS)-2 is that the suspended sediment concentration (SSC) indirectly measured by the YSI and the acoustic Doppler current profiler (ADCP) has a low accuracy, which limits the estimation of the sediment distribution under strong tidal current conditions
The accurate measurement of the sediment distribution in the water column is important to understand the coastal processes in macrotidal areas
Summary
Coastal waters are interfaces between land and ocean and are important for human life because of their geographical proximity as well as their function as food, transportation, and recreation sources. One example of a bottom-fixed instrument is a wave gauge that measures the pressure of the water column and converts it into surface elevation based on linear wave theory. Acoustic sensors, such as the Nortek Acoustic Wave and Current Profiler (AWAC; Pedersen et al, 2007), are mounted on a bottom-fixed frame facing upward to measure waves and currents (Jeong et al, 2020). Mooring buoys are surface buoys that are moored in coastal waters to measure physical, meteorological, and biogeochemical data (Dorman and Winant, 1995; Bailey et al, 2019) They are connected to the seabed by mooring lines and facilitate observation of the subsurface water column via instruments attached to the mooring lines
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