How can we measure the Coastal Currents of Gangneung?

1. Where is Gangneung?

Gangneung is a city in Gangwon-do, South Korea. It faces the eastern coast of the Korean Peninsula. It's an historic and culturally wealthy city with a stunning coastal setting which sees hundreds of tourists each year.

The landscape around Gangneung is varied: the coastline contains sandy beaches, like Gyeongpo Beach, and rocky outcrops. The city is nestled between mountains and the sea-the view from here is great. The local people are involved in different occupations, such as fishing, tourism, and traditional industries.

The East Sea, or Sea of Japan, that borders Gangneung is a cold body of water that contains a particular marine ecosystem. It is home to a wide variety of fish species, including salmon and pollock. The sea is also home to seaweed beds, which form part of the important part of the local marine food chain. Coastal waters greatly impact the local climate, as its cool sea breezes moderate the temperature.

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

Various elements come into play in determining the characteristics of coastal currents near Gangneung. First and foremost among them are the dominant ocean currents around the East Sea. The Tsushima Current, a warm-water current, along with the Liman Current, which is cold water in nature, runs across this area. The Tsushima Current normally moves northward, carrying relatively warm and nutrient-rich waters, whereas the Liman Current moves southward and is colder.

Tidal currents also play a very significant role. Very great tidal ranges in the area make the ebb and flow of the tides result in complex current patterns. The shape of the coastline and the general underwater topography contribute to this complexity of the current situation. Underwater reefs, shoals, and channels may cause the currents to diverge, converge, or develop eddies. Besides, the wind patterns, especially strong wind blowing over the East Sea, may drive the surface current and mix different layers of water.

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

Surface Drifting Buoy Method: A surface - drifting buoy can be released into the water to observe surface current. The movement of a buoy is traced in time using GPS or other tracking systems. However, it does have its limitations. Firstly, this method provides information regarding the surface current only. Secondly, the reading could be interfered with by wind or waves. For instance, if a strong wind had blown the buoy in a direction different from the actual current, it may lead to incorrect readings of the current's direction and speed.

Anchor - Boat Method: Current can be measured by an anchored boat. Instruments are submerged from the anchored boats into the water, measuring currents at different depths. While this enables detailed depth - wise measurements, there are some drawbacks to it. The fixed position of the boat restricts the area of measurement in which it might not capture the full variability of a large coastal area.

ADCP Method: The ADCP current meter method is advanced and more efficient for measuring the coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to compute the velocity of water at different depths. It provides a more comprehensive profile of the current from the surface down to the bottom of the seabed. In this way, ADCPs are not substantially affected by surface disturbances and may operate without interruption over longer times, building up an accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

The ADCPs work on the principle of the Doppler Effect. They send high-frequency 'chirps' of acoustic pulses into the water. When these pulses encounter particles of water in motion, their reflected pulses return with a different frequency from the original emitted pulse. If the water particles are moving towards the ADCP current profiler, then the frequency of the reflected signal is higher than the emitted signal; if they are moving away, it is lower.

The ADCP flow meter has four transducers that transmit and receive signals at different angles. By analyzing the Doppler shifts from various directions and at different depths, the device is able to calculate the three-dimensional velocity of the water. Thus, it measures the horizontal and vertical components of the velocity so that a thorough understanding of the structure and behavior of the current may be discerned.

5. What is required to achieve high - quality measurement of Gangneung coastal currents?

For high - quality measurement of the coastal currents near Gangneung, the equipment should be made of reliable materials. Since the marine environment is very harsh, with cold water, saltwater, and sometimes stormy conditions, the casing must be in a durable format. The device should be compact for easy deployment and retrieval processes, which may be complicated by the specific form of a coastal area.

A light design is preferable for better manageability of the equipment when being installed or maintained. Low consumption is essential for having long-and autonomous-operation. Cost-effectiveness is also a target to obtain large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy is vastly resistant to corrosion, which is very important in the light of seawater's corrosive effects. It is also strong and durable, to bear the pressure of water at respective depths. Its lightweight nature makes it more convenient for various deployment methods.

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

First, use purpose should be considered when choosing the equipment for current measurement near Gangneung. If the measurement is for a vessel navigating or short-term research, a ship-mounted ADCP flow meter would be suitable. It gives 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.

Considering the frequency of ADCPs, for the water depth up to 70m, a 600kHz ADCP would be suitable. For depths up to 110m, a 300kHz ADCP would be appropriate, while for deeper waters that could be found near Gangneung, such as 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.