How do we measure the Coastal Currents of Gunsan?

1. Where is Gunsan?

Gunsan is a city located in North Jeolla Province, South Korea. It lies on the southwestern coast of the Korean Peninsula and is well faced to the Yellow Sea. The city is also an important port and industrial center.

The landscape of Gunsan thus combines the busy port areas with the natural coastal characteristics. It has a huge, well-equipped port facility that is capable of receiving and shipping almost all varieties of cargo, from containerized goods to grains, petrochemical products, and raw materials. Besides the sandy beaches and mudflats, industrial aspects include, but are not limited to, the presence of container terminals. The local community engages in shipping, manufacturing industries, fisheries, and servicing for both the port and tourist industries.

The Yellow Sea around Gunsan is a semi-enclosed sea, and it abounds with a variety of fish such as flounder and eel, as well as a lot of shellfish. In addition, the beds of seaweed are quite broad in width. The tides form the most important phenomenon around the coasts. This big tidal range has the water moving in and out of the bays and over the mudflats, affecting the local ecosystem and the currents near the coast.

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

These different factors interact to determine the coastal currents around Gunsan, tidal currents are dominant, while the large tidal range of the Yellow Sea leads to complex current patterns due to the ebbing and flooding of water. The coastline geometry and underwater topography make another major impact, the general shapes of the port infrastructure, mudflats, and sandbars underwater make the current either diverge, converge, or form eddies.

The inflow of freshwater through local rivers and canals may affect the salinity and density of the water in the coastal area and, therefore, the flowing current. Besides, wind conditions-meteorological factors-most of all seasonal winds blowing over the Yellow Sea-drive surface currents and influence the mixing of various water layers. The shipping activities in the port can also have a small effect on the local current through ships' traffic and displacement of water mass.

3. Observation of Gunsan's coastal water flow

Surface Drifting Buoy Method: Surface - drifting buoy released on the water can see surface current. The travel position of a buoy would then be measured over periods with the aid of Global Positioning System or related. However, the approach has limitations. It is only useful for the surface current alone and is prone to changes in wind and waves. In cases where the buoy is moved by a strong wind in the opposite direction to that of the actual current, this method can lead to inaccuracies regarding the direction and speed of such currents.

Anchor-Boat Method: Current could also be measured by an anchored boat. Instruments used to measure the current are lowered from it into the water at depth. While this will give a more detailed depth-wise measurement, it also has disadvantages. The fixed position of the boat restricts the area of measurement and may not capture the full variability of the currents in a large coastal area.

ADCP Method: This is more advanced and effective in the measurement of coastal currents. In ADCPs, the acoustic signals are emitted into the water and the Doppler shift of the reflected signals determines the velocity of water at different depths. The profile in this regard is far more extensive, from the surface down to the seabed. They are less affected by the surface disturbance and can keep operating continuously for long periods, giving a more realistic picture of the current structure.

4. How does the principle of Doppler work in ADCPs?

The working of ADCPs is based on the Doppler effect. They transmit high-frequency acoustic pulses into the water. When these pulses interact with moving water particles, the frequency of the reflected pulses changes. 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 many transducers, which shoot and receive signals at several angles. Through the analyzing of Doppler shifts at different directions and depths, the device calculates the three-dimensional velocity of the water. This means it computes the horizontal and vertical components of velocity, hence providing a rather detailed understanding of the current structure and behavior.

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

For high-quality measurement of the coastal currents near Gunsan, the equipment should be manufactured with reliable materials. With the marine environment, consisting of saltwater, and the possible exposure to storms, influence of tides, and port activities, a casing that is durable is called for. The size of the equipment should be small to allow easy deployment and retrieval, taking into consideration the complex topography of the coastlines, which contains a port, beaches, and mudflats.

The 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 an important factor in enabling large - scale measurements.

The casing of ADCPs is preferably made of a titanium alloy. Titanium alloy has excellent corrosion resistance, especially against seawater. The material is strong and resilient to withstand water pressure from different levels. Being lightweight makes the deployment more practical through various means.

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

First, when choosing the equipment for current measurement near Gunsan, consider the purpose of use. For the measurement of a vessel's navigation or short-term research, a ship-mounted ADCP flow meter is suitable. 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.

Regarding the frequency of ADCPs, a 600kHz ADCP will be adequate for water depths up to 70m. For up to 110m, a 300kHz ADCP is suitable. And for deeper waters, which might be found near Gunsan-for example, areas with depths over 1000m-a 75kHz ADCP would be 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.