How do we measure Sokcho's Coastal Currents?

1. Where is Sokcho?

Sokcho is a city in Gangwon-do, South Korea, located along the eastern coast of the Korean Peninsula. It boasts beautiful natural landscapes and is thus one of the country's most popular tourist destinations. This city is surrounded by the East Sea-beautifully known as Sea of Japan-which gives it an edge over other areas, with a unique coastal appeal.

The landscape of the area surrounding Sokcho is varied. These include beaches with sand, such as Sokcho Beach, where many people visit in summer. Further, the coastline contains rocky cliffs with small islands offshore that contribute to the visual spectacle. The city itself is a bustling potpourri of traditional Korean culture and modern facilities. The people within this city are deeply involved in various professions, fishing, hospitality, and small-scale manufacturing.

The sea off Sokcho is cold, with a very viable marine ecosystem that hosts numerous fish species, such as herring and flounder, varieties of shellfish, and types of seaweed. This body of water contributes much to the climate of the area by carrying cool sea breezes inland during the hotter months and helping to regulate the ambient temperature during the year.

2. What is the state of the coastal currents off Sokcho?

The coastal currents off Sokcho are influenced by several conditions. The general currents in the East Sea prevail. An interaction in this area occurs between the Tsushima Current, which is a warm-water current, and the Liman Current, which is a cold-water current. The Tsushima Current typically flows northward and carries relatively warm, nutrient-rich water. In contrast, the Liman Current flows to the south and is colder; this sets up a dynamic where these two currents interact with each other in a dynamic environment.

Tidal currents are another great factor. The tidal range is quite extensive in the area, and between the ebb and flow of tides, their interactions bring about complicated current patterns; this is influenced by the shape of the coastline and the underwater topography. In addition, bottom topography with underwater reefs, shoals, and channels may lead to current deflection, convergences, or eddies. The wind patterns, particularly the prevailing strong winds across the East Sea, drive surface currents and affect the mixing between different layers.

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

The surface drifting buoy method: a buoy with a surface-drifting capability is discharged into the water, by which the surface current is observed. The position of this buoy is tracked over time with the use of GPS or any tracking device. This method again has its shortcomings. It gives information about the surface current only and may be influenced by wind and waves. For example, if a strong wind blows the buoy in a different direction from the actual current, it can lead to inaccurate measurements of the current's direction and speed.

Anchor-Boat Method: Current could be measured by an anchored boat. The instruments are lowered from the anchored boat into the water at depth intervals to measure the current. While this method provides a greater range of depth-wise measurements, it has certain disadvantages. Since the location of the boat is fixed, there is only a limited area over which measurement can be carried out. This may not reflect the full range of variation of the currents in a big coastal area.

ADCP Method: The measurement of the currents in the coast by using the ADCP current meter method is more advanced and gainful. 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 provides a more comprehensive profile of the current from the surface to the seabed. Because ADCPs are less affected by surface disturbances, they are able to provide a more accurate picture of the current structure for longer continuous monitoring periods.

4. How do the ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler effect. They transmit high-frequency acoustic pulses into the water. Once these pulses come in contact with the moving particles of water, the frequency of the pulses reflected back changes. When the water particles are moving towards the ADCP current profiler, the frequency of the reflected signal is higher than the emitted signal, and when away, it becomes lower.

The ADCP flow meter has several transducers, which send and receive signals at different angles. Depending on the Doppler shifts from various angles and different levels, the device will calculate the three-dimensional water velocity, which will include the horizontal and vertical components, hence detailed knowledge of the structure and behavior of the currents.

5. What is required for high-quality measurement of coastal currents off Sokcho?

High-quality measurement of the coastal currents off Sokcho requires that the equipment be made of reliable material. Since it is in a harsh marine environment, cold water, saltwater, and possible storm exposure require a casing to be durable. The size of the device needs to be as compact as possible in order to enable its easy deployment and retrieval, especially in areas of complex coastline.

A light design will be preferred since it allows easy handling during installation and maintenance. Low power consumption is important since the node is intended for long-term or autonomous operations. Cost-effectiveness is also relevant to realize large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. The corrosion resistance of a titanium alloy is excellent, which plays a vital role in withstanding the corrosive effects of seawater. This metal is tough and can withstand pressures of water at different depths. It is lighter in weight, making it more convenient in various deployment methods.

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

When choosing equipment for current measurement near Sokcho, consider the purpose of use first. If the measurement is for a vessel's navigation or short - term research, a ship - mounted ADCP flow meter is a suitable option. 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 appropriate. The near-bottom current will again be well captured by it. If the monitoring of the coastal current needs to be both long term and over a wide area, it would be appropriate to mount a buoy-type ADCP current profiler.

Frequency of ADCPs: For water depths up to 70m, a 600kHz ADCP would be a good choice. In the case of up to 110m depth, a 300kHz ADCP is appropriate. For even deeper waters, which might be the case near Sokcho, with areas over 1000m in depth, a 75kHz ADCP 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.