How can we measure the Coastal Currents of Uljin?

1. Where is Uljin?

Uljin is the county in Gangwon-do of South Korea and is on the east coast of the Korean Peninsula. Uljin is a place of natural beauty, bordered by the East Sea, or Sea of Japan, along its coastline. The topography varies between sandy shores and rocky shores with, sometimes, grassy woods touching upon the sea.

Local people's livelihood depends on fishing, tourism, and agriculture. People in Uljin are very closely related to the sea because fishing is an important industry in their lives. The East Sea off Uljin is cold water with abundant resources. It holds plenty of species of fish like mackerel, sardines, flatfish, and many kinds of shellfish and seaweed.

It is also very crucial in the determination of the local climate. Ocean currents are cold, and sea breezes bring moisture that helps moderate the temperature and thus creates a relatively mild climate. Coastal areas are popular for fishing, going to beaches, and for the rich marine ecosystem exploring through diving and snorkeling.

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

Many various factors influence the features of coastal currents around Uljin. It is very important to mention the general major ocean currents in the East Sea. Here, the warm-water Tsushima Current and the cold-water Liman Current interact. The Tsushima Current generally flows northward with relatively warm and nutrient-rich water, while Liman Current moves southward and is colder.

Not to be underestimated is the power of tidal currents. There is a substantial tidal range in the area, with complex current patterns developing during the ebb and flow of the tides. This is partly because of the shape of the coastline and underwater topography. Underwater ridges, shoals, and channels can make the currents change direction and speed. Besides, the wind regime, in particular strong wind quite common in this area, is able to force surface currents and impact the mixing of different water layers.

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

Surface Drifting Buoy Method: A surface - drifting buoy can be used to track the surface current. The buoy is dropped in the water and its path is tracked over a period, usually by GPS or any other tracking device. However, there are disadvantages associated with this method. It only can give information on the surface current and may be influenced by wind and wave actions. A good example is when strong onshore wind may just push the buoy towards the beach and thus yield an inaccurate result of the direction of the current.

Anchor - Boat Method: One of the several ways the current can be measured is by using an anchored boat. Instruments are lowered from the boat into the water at different depths to measure the current in that area. However, this allows for more detailed depthwise measurements. This has its drawbacks. The fixed position of the boat limits the area of measurement, which may not capture the full variability of the currents in a large coastal area.

ADCP Method: Being more advanced and efficient, the ADCP current meter method of measurement of coastal currents is performed. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals in order to calculate the velocity of the water at different depths. It provides a more comprehensive 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, therefore giving a more accurate picture of the current structure.

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

They work on the principle of the Doppler effect. ADCPs transmit high-frequency 'chirps' of acoustic energy into the water. When these pulses of energy come into contact with moving water particles, the frequency of the returning pulses is different. If the water particles are moving towards the ADCP current profiler, then the frequency of the returning signal is higher than the transmitted signal; if they are moving away, it is lower.

The ADCP flow meter has several transducers that send and receive signals at various angles. By analyzing the Doppler shifts from different directions and at different depths, the device can calculate the three-dimensional velocity of the water. This means it can measure the horizontal and vertical components of the velocity; thus, detailed insight is obtained into the structure and behavior of the current.

5. What is necessary for high-quality measurements of Uljin coastal currents?

For high-quality measurement of the coastal currents near Uljin, the devices for measurement shall contain reliable materials. Given the very harsh marine environment, consisting of cold water, saltwater, and possibly storm exposure, a casing should be strongly durable. Its dimensions should also be as compact as possible, so the work of deploying and retrieving it will be easier, especially if there is some complications in coastal view.

A light design is preferred since the equipment is much easier to handle during installation and maintenance. In general, it should consume low power for long -term and autonomous operation. Cost effectiveness is also another strong factor in order to perform large scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is important for resisting the corrosive impact of seawater. Besides being strong and resilient, it resists the pressure of 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?

First, it is necessary to choose equipment for current measurement around Uljin, considering the purposes for which it will be used. If the measurement is intended for the navigation of a vessel or short-term research, a ship-mounted ADCP meter would work just fine. It gives real-time current information to the ship during the voyage.

When measurements have to be made near the seabed, as in studies on sediment transport or benthic ecology, a bottom-mounted ADCP is preferred, since the details of the near-bottom current can be captured. Long-term and wide-area monitoring of coastal current will have a buoy-type ADCP flow meter as ideal.

For the frequency of ADCPs, one that is 600kHz would be suitable for water depths up to 70m, a 300kHz ADCP for those with an upper limit of around 110m, while for further waters that could be off Uljin where depths are over 1000m, then a 75kHz type of ADCP current profiler 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.