How to measure the Coastal Currents of Hongseong?

1. Where is Hongseong?

Hongseong is a county in South Chungcheong Province, South Korea. It lies on the western coast of the Korean Peninsula, which faces the Yellow Sea. The area is popularly recognized for its beautiful coasts that are composed of sandy beaches, tidal flats, and small fishing villages.

Agricultural fields and mountains also form part of the local landscape. Its economy is sustained by fishing, agriculture, and tourism. Fishing relies on the Yellow Sea. There are various fish species such as flounder, anchovy, and small crabs in the sea around Hongseong. Shellfish abound in the tidal flats, where migratory birds visit for feeding.

The sea gives a great modification to the climate in Hongseong. The Yellow Sea sea breezes bring a modification in the temperature of the area and make it quite pleasant. During summer, the sandy beaches are filled with tourists, and seafood is a highlight of the local cuisine.

2. What is the situation of the coastal currents near Hongseong?

The coastal currents around Hongseong are influenced by a lot of factors. Tidal currents come first. The tidal range of the Yellow Sea is quite huge, and the ebb and flood result in a complex structure of current. Water flow into and out of tidal flats and bays, creating such dynamic flow.

The other factor is the shape of the coastline and underwater topography. These would be modified by the currents' directions and speed, given the presence of tidal flats, sandbars, and underwater channels. For example, water can be slowed as it spreads over wide tidal flats at low tide and speeds up while being funneled through a narrow channel at high tide. It influences salinity and density by the inflow of freshwater from local rivers and streams, which in turn affects the flow of the current. Besides, the wind patterns, especially seasonal winds that blow across the Yellow Sea, drive surface currents and affect mixing within different layers of water.

3. How to observe the coastal water flow of Hongseong?

Surface Drifting Buoy Method: In this method, a surface-drifting buoy is released in the water to observe the surface current. The movement of the buoy is tracked over time using GPS or other tracking systems. However, this method has certain limitations. It only provides information about the surface current and can be affected by wind and waves. For example, when the buoy is blown by strong wind in a different direction than the current actually is, it will lead to inaccurate measurements with respect to the direction and speed of the current.

Anchor - Boat Method: Currents can also be measured by an anchored boat. Instruments are lowered in the water from the anchored boat to measure the current at different levels of depth. Although this yields more detailed depth - wise measurement, it also has disadvantages, the fixed position of a boat restricts the measurement area, and it may not capture full variability of currents in the large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current meter method is more advanced and efficient in the measurement of coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of water at different depths. This gives a full profile of the current right from the surface to the seabed. ADCPs are less affected by surface disturbances and can operate continuously for long periods, giving a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

The principle of operation of ADCPs is based on the Doppler effect. They send high-frequency acoustic pulses into the water. Due to the interaction with moving water particles, the frequency of the reflected pulses is changed. If the movement of water particles is towards the ADCP profiler, the frequency of the reflected signal is higher than the emitted one; if they are moving away, it is lower.

Indeed, several transducers are fitted on one ADCP meter, which can emit and receive signals at varied angles. By analyzing these different directional and depth levels through Doppler shifts, the device becomes capable of calculating the three-dimensional velocities of water. That would come out to be the determination of horizontal and vertical components of the velocity, so there it does much in giving a deep view of the structure of current and its behavior.

5. What are the requirements for good-quality measurement of Hongseong coastal currents?

The equipment should be made of reliable materials for high-quality measurement of the coastal currents around Hongseong. It should have a durable casing because of the marine environment, including saltwater, potential storms, and the influence of tides and tidal flats. The size of the equipment should be small to enable easy deployment and retrieval, especially in the complex coastal landscape with its beaches, tidal flats, and fishing villages.

A lightweight design is preferred as it renders the equipment easy to handle during both installation and maintenance. Long-term and autonomous operation imposes the need for low-power consumption. For large-scale measurements, cost-effectiveness is relevant.

The housing for ADCPs is preferably to be of titanium alloy. For its perfect resistance to corrosion, that is so important for surviving corrosive effects of sea water. Besides, it's very strong and able to cope with pressure depending from the depth of water. Also, it's lighter in several respects for a number of ways of deployment.

6. How to choose right equipment for current measurement?

If one chooses equipment for current measurement near Hongseong, it will be necessary to think about the purpose of the use first. If this measurement is to navigate a vessel or do short-term research, then a ship-mounted ADCP flow meter will suffice. It provides real-time current information during the voyage.

For measurements near the seabed, such as for studying sediment transport or benthic ecology, a bottom - mounted ADCP is preferable. It can capture the details of the near - bottom current. If long - term and wide - area monitoring of the coastal current is required, a buoy - type ADCP current profiler is ideal.

In general, concerning the frequency of ADCPs, the 600kHz ADCP would be suitable for water depths up to 70m, a 300kHz ADCP for water up to 110m depth, and for deeper waters, such as over 1000m, possibly around Hongseong, a 75kHz ADCP is suitable.

There are well - known ADCP current meter brands such as Teledyne RDI, Nortek, and Sontek. However, a Chinese brand, China Sonar PandaADCP, is also worth considering. It is made of all - titanium alloy material and offers an excellent cost - performance ratio. You can find more information on their website: https://china-sonar.com/.

Here is a table with some well known ADCP instrument brands and moels.