How to measure the Coastal Currents of Goheung?

1. Where is Goheung?

Goheung gun, South Jeolla Province of South Korea, is on the southern coast of the Korean Peninsula, and it is full of natural beauty and rich maritime traditions. The area has a long coastline that includes sandy beaches, rocky cliffs,and small fishing villages.

The local landscape also boasts beautiful mountains that meet the sea, creating a stunning backdrop. The county is dotted with historical and cultural sites, such as ancient temples and fortresses. The local population is engaged in fishing, agriculture, and tourism. Fishing is an important part of the local economy since the South Sea near Goheung is teeming with marine life.

The South Sea off Goheung is a warm water sea, hosting all kinds of fish, such as mackerel, tuna, and anchovy. There are also great beds of seaweed and shellfish. It plays an important role in the climate, as it brings in warm, humid air and moderates the temperature. The sandy beaches and clear waters make it a popular destination for beach goers and water sports enthusiasts.

2. What is the situation of the coastal currents around Goheung?

Various elements influence the coastal currents near Goheung. The main ocean current around the area is the Tsushima Current, which is a warm water current generally flowing northward through the Korea Strait. It carries warm and nutrient rich waters that greatly affect the local marine ecosystem and the coastal currents.

Tidal currents are another great influence. There is a substantial tidal range around Goheung, and the ebb and flow of the tides create very complicated current patterns. The shape of the coastline and underwater topography are very important. Rocky cliffs, sandy beaches, and underwater ridges can make the currents change direction and speed. Moreover, the wind patterns, especially the seasonal winds, can drive the surface currents and influence the mixing of different layers of water.

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

Surface Drifting Buoy Method: In this method, a surface drifting buoy is allowed to release into the water to observe the surface current. Further, the position of the buoy is tracked after regular time intervals using GPS or other tracking systems. However, this technique has its limitations. It provides information only about the surface current and is susceptible to wind and waves. For instance, 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: In this method, an anchored boat is used to measure the current. The instruments are lowered from the anchored boat into the water to measure the current at various depths. While this offers the advantage of more detailed depthwise measurements, it also presents disadvantages. The fixed position of the boat restricts the area in which measurement can be carried out, and may not capture the full variability of the currents in a large coastal area.

Acoustic Doppler Current Profiler Method: The ADCP current meter is an advanced and more proficient way of measuring the coastal currents. ADCPs send acoustic signals into the water, measure the Doppler shift of the reflected signals, and therefore calculate the velocity of the water at different depths. This therefore provides a more comprehensive profile of the current from surface to seabed. Because ADCPs are less affected by surface disturbances, they can often operate continuously over long periods and give a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

ADCPs operate based on the Doppler effect. They emit high frequency acoustic pulses into the water. When those pulses interact with moving water particles, the frequency of the reflected pulses is changed. If the water particles are moving towards the ADCP profiler, the frequency of the reflected signal is higher than the emitted signal; if they are moving away, it is lower.

The ADCP meter has multiple transducers, which send and receive signals at different angles. With the analysis of the Doppler shifts from different directions and at different depths, this device can calculate the three dimensional velocity of the water. It means that it is able to determine the horizontal and vertical components of the velocity, with a detailed understanding of the structure and behavior of the current.

5. What is required for the measurement of high quality Goheung coastal currents?

For high quality measurement of the coastal currents near Goheung, the equipment should have reliable materials. Given the marine environment, with saltwater, potential exposure to storms, and the influence of tides, a durable casing is essential. The equipment's size should be small for easy deployment and retrieval, especially considering the complex coastal landscape with its cliffs and beaches.

A lightweight design is preferred because it makes the equipment more manageable during installation and maintenance. Low power consumption is necessary for long term and autonomous operation. Cost effectiveness is also important to enable large scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is very important for resisting the corrosive effects of seawater. It is also strong and durable to bear 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?

If there is a purpose for selecting equipment for the measurement, the first factor to check would be its purpose for use. It would require a ship mounted ADCP flow meter to suit the navigation or short term research of a vessel. These ship mounted types provide the real time current information of the currents 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.

Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP is a good choice. For depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters that might be found near Goheung, such as areas with a depth over 1000m, 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.