How can we measure the Coastal Currents of Geoje?

1. Where is Geoje

Geoje is one of the cities in South Gyeongsang Province, South Korea. It is a coastal city lying in the southern part of the Korean Peninsula, overlooking the South Sea, more popularly called Korea Strait. It has beautiful islands and pristine beaches with a very rich maritime history.

The Geoje landscape is a mix of hilly terrains and quite a long coastline. In addition, there are many islands off Geoje, such as Oedo Island, which are popular with tourists. These islands are not only a feast for the eyes, with their lush vegetation and clear waters, but also a good opportunity to explore the diversity of the coastal ecosystems. Local people earn their livelihood by fishing, shipbuilding, and tourism. It is also famous for its shipbuilding industry, which boasts large shipyards contributing both locally and nationally.

The South Sea near Geoje is a warm water body that contains a variety of marine life. It is a home to many fish species, including sea bream, mullet, and anchovy. In the coastal waters, extensive beds of seaweed and shellfish are found. The sea has a great influence on the local climate, and the temperature is moderated with sea breezes. Sandy beaches and coves along the coast are perfect for water-based recreational activities such as swimming, snorkeling, and boating.

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

The coastal currents off Geoje are influenced by several variables. The major ocean current is the Tsushima Current, a warm-water current that generally flows northward through the Korea Strait. The inflow of warm and nutrient-rich water brought about by this current has a great effect on the local marine ecosystem and, by extension, the coastal currents.

Tidal currents also play a very powerful role. Geoje experiences a considerable tidal range, and the ebb and flow of the tides lead to the formation of complex current patterns. The shape of the coastline and the underwater topography play an important role. The presence of islands, shallow areas, and underwater channels can cause the currents to change direction and speed. Besides, the wind pattern, particularly the seasonal wind, might force the surface current and mix different layers of water.

3. How to observe the Geoje coastal water flow?

Surface Drifting Buoy Method: A surface - drifting buoy is released into the water to observe the surface current. Then, the movement of a buoy is tracked over some time using GPS or any other tracking system. This method has its drawbacks. It is limited to the surface current alone and may be affected by the wind and waves. Suppose there is a strong wind blowing the buoy in another direction from the actual current, then it may give inaccurate measurement of the direction and speed of the current.

Anchor-Boat Method: An anchored boat could be employed in the measurement. Instruments are put down into the water from this boat, which measure at discrete depth levels. The disadvantage is that while there can be more depthwise detail, this method is at a disadvantage when trying to understand the full range of currents that may be developed over any large coastal region.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP current meter method is a more sophisticated and efficient way of measurement of the 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 will give a better profile of the current right from the surface to the seabed. The ADCPs are far less sensitive to surface disturbances and therefore can run continuously over quite long periods, giving far more realistic information about current structure.

4. How does an ADCP using the principle of Doppler work?

ADCPs work on the principle of the Doppler effect. They send high-frequency acoustic pulses into the water. In the case of interaction with moving water particles, the frequency of the reflected pulses changes. If the water particles are moving towards the ADCP current profiler, the frequency of the reflected signal is higher than the emitted one; in the case of movement in the opposite direction, it is lower.

The ADCP profiler has multiple transducers that send and receive signals at different angles. By analyzing the Doppler shifts from different directions and at different depths, the device can calculate the three-dimensional velocity of the water. That means it can determine the horizontal and vertical components of the velocity, providing a detailed understanding of the current's structure and behavior.

5. What is needed for high-quality measurement of Geoje coastal currents?

It will be appropriate if the equipment for the measurement of the coastal currents around Geoje is made from reliable materials. The saltwater, the probable exposition to storms, and the tide's action mean that this casing should be strong enough. The equipment's size shall be small, for ease of deployment and retrieval, with the complex topography that characterizes most coasts with islands and coves.

A lightweight design is highly desirable, since it ensures that the equipment is lightweight and easy to handle on site during installation and when performing maintenance. The sensor elements should have low power consumption for long-term and autonomous operation; cost-effectiveness for large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is vital for withstanding the corrosive effects of seawater. It is also strong and durable, capable of withstanding the pressure of the water at different depths. Its lightweight nature makes it more convenient for various deployment methods.

6. How to Choose the right equipment for current measurement?

For current measurement near Geoje, first, the purpose of the use should be considered to choose the equipment. The proper equipment for a ship navigating or short-term research will be the ADCP meter mounted on the ship, which can provide current information in real time during a 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 flow meter is ideal.

Regarding the frequency of the ADCPs, for up to 70m water depths, a 600kHz is a good choice. An ADCP current profiler of 300kHz is more appropriate when the depth is up to 110m. For deeper water that might be found near Geoje, such as depths over 1000 meters, a 75kHz is recommended.

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.