How to measure the Coastal Currents of Pohang?

1. Where is Pohang?

Pohang is a colorful city situated in the Gyeongsangbuk - do province, lying on the southeast coast of the Korean Peninsula in South Korea. Between those granite-peak-like mountains and the expansiveness of the East Sea-sea of Japan, it presents an interesting combination of natural and artificial scenery.

It is a city that has been highly regarded for its lovely coastline elegantly curving along the sea. Indeed, the city boasts of having a number of sandy beaches where locals and visitors rush to enjoy the sun, sand, and sea. The coastal areas are dotted with small fishing villages that, through the years, have retained much of their traditional charm. These villages are a treat to the eyes and also reflect the long relationship with the sea that this city has shared for ages, as fishing has been one of the prime sources of local livelihoods.

Pohang is a busy economic city that has diverse industries. It is home to the world - famous POSCO (Pohang Iron and Steel Company), which has played a significant role in shaping the city's growth and development. The presence of this giant in the steel industry has led to the emergence of numerous related industries and a large workforce. Besides industry, the city also has a rich cultural heritage. There are historical sites, museums, and cultural festivals that showcase the particular traditions and history of the region.

The East Sea, which is situated adjacent to Pohang, is a dynamic water body. It is referred to for the cold-water currents and possesses a rich level of marine life. It has a wide variety of fish species such as mackerel, herring, and pollock. Seaweed beds also abound to contribute to the local marine ecosystem and are a very vital ingredient in the food and pharmaceutical industries. The influence of the sea extends right through into the local climate in the form of cool sea breezes during the hotter summer months and generally regulates the temperature throughout the year.

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

The nature of the coastal currents around Pohang is influenced by many factors. First, the major ocean currents play an important role. The East Sea presents one of the few locations in the world where a warm-water current, the Tsushima Current, and a cold-water current, the Liman Current, interact. The Tsushima Current normally flows northward along the western coast of Hokkaido with relatively warm and nutrient-rich water. In contrast, the Liman Current moves southward and is colder. The interaction between the two currents generates an intricate and dynamic scenario where water properties and flow directions are under continuous variation.

The tidal currents are also among the predominant ones. Indeed, the tidal range experienced in this area is very large; the ebbs and flows associated with the tides create the complex current pattern. If at high tide the water rushes towards the coast, at low tide it retreats, meaning that the coastal currents change character in strength and direction.

The shape of the coastline and the underwater topography are important contributors. Underwater ridges, shoals, and channels can lead to divergence, convergence, or eddy formations of currents. For example, when water comes across a submerged ridge, it is forced to change its course and thus changes its direction of current and velocity. Moreover, the wind pattern, especially strong winds that usually visit the area, is able to drive surface currents and affect the mixing of different layers of water. Dominant winds from the north or south can push the surface water in a certain direction, adding another layer of intricacy to the coastal current system.

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

Surface Drifting Buoy Method: A surface - drifting buoy can be deployed to observe the surface current. The buoy is released into the water and its movement is tracked over time, usually with the help of GPS or other tracking technologies. This allows us to monitor the direction and speed at which the buoy is carried by the surface current. However, this method has its limitations. It also carries information about the surface current only and is easily affected by wind and wave action. For instance, if the wind in the opposite direction to the current's direction is strong, the buoy will be pushed off-course, giving incorrect readings of the direction and speed of the current.

Anchor-Boat Method: The current can be measured using an anchored boat. Instruments are lowered from the boat into the water to measure the current over different depths. This allows a more detailed insight into the vertical profile of the current. However, it also has its drawbacks. The fixed position of the boat limits the area over which this is measured and may not capture the full variability of the currents in a large coastal area. Moreover, deployment and retrieval in general are quite difficult and time-consuming from the boat, especially in stormy sea conditions.

Acoustic Doppler Current Profiler (ADCP) Method: ADCP current meter is more advanced and efficient to measure coastal currents. It transmits acoustic signals into the water and measures the Doppler shift of the reflected signals to calculate the velocity of water at different depths. This gives a full profile of the current from surface to seabed. The ADCPs are less susceptible to problems with surface disturbance than the buoy method and, once deployed, can function for long periods without servicing, yielding a more accurate picture of the current structure. They are highly versatile, being mounted on different platforms of boats, buoys, or fixed structures, depending on the specific measurement requirements.

4. How do ADCPs based on the Doppler principle work?

The ADCPs work on the basis of the Doppler effect. They emit high-frequency acoustic pulses into the water. In interactions with moving water particles, the frequency of the reflected pulses changes. If the water particles are moving towards the ADCP current profiler, then the frequency of the reflected signal is higher than the emitted one, while if they are moving away, it is lower.

Accordingly, the ADCP flow meter is fitted with several transducers that send and receive signals at various angles. In analyzing the Doppler shifts from various directions at varied depths, it computes the three-dimensional velocity of the water. By this, it means the horizontal and vertical components can be derived to give an insightfully detailed understanding of the structure and behavior of the current. For instance, it may indicate how the current changes from the surface, possibly affected by wind and waves, down to the seabed, with interactions with the bottom topography.

5. What's needed for high - quality measurement of Pohang coastal currents?

The equipment to be used for measuring the currents near Pohang's coast should have a few important features. First, the materials from which it is made must be of good quality. Considering that the marine environment is rather harsh due to cold water, saltwater, and probably storms, the casing shall be durable. It needs to be resistant to the corrosive action of seawater and to the mechanical load generated by waves and currents over a long period.

The equipment should be of small size for easy deployment and retrieval, especially considering the complexity of the coastal landscape around Pohang. Since a smaller size is more convenient for installation in various locations, ranging from a small boat or buoy to a relatively narrow coastal area, this requirement ensures that potential applications are maximized.

A lightweight design is preferred, as it makes the equipment more manageable during installation and maintenance. It reduces handling effort for such equipment, even when working under difficult marine conditions. Low power consumption can be translated to long-term and autonomous operation. This allows the equipment to operate continuously without requiring it to frequently change batteries or rely on sources of external power that might be inappropriate or impractical in some remote coastal locations.

Besides, cost-effectiveness is also an important factor that will enable large-scale measurements. The casing of ADCPs is preferably made of Titanium alloy. The use of Titanium alloy is important because it bears excellent corrosion resistance, a very vital factor needed when dealing with the corrosive effects of seawater. It is also strong enough and durable to bear the pressure of the water at different depths. Besides, due to its lightweight nature, it is more suitable for a variety of deployment methods, whether on a floating platform or fixed to the seabed.

6. Selection of current-measuring equipment

The purpose of use must be considered in front when choosing equipment for current measurement near Pohang. A measurement target is used for a vessel's navigation or short-term research, and the suitable option is a ship-mounted ADCP meter. It will provide real-time current information during the voyage and will enable the vessel's crew to decide about course and speed on some positions.

A bottom-mounted ADCP flow meter is preferred for measurements near the seabed-for instance, for studies of sediment transport or benthic ecology. It can capture the details in the near-bottom current that are very important in understanding the interaction between the water and the seabed and how it affects the movement of sediments and, by extension, the survival of benthic organisms.

In case long-term and wide-area monitoring of the coastal current is required, ADCP current profiler of buoy type would be ideal. It can then be deployed at a fixed location in water for a long period and continuously transmit data regarding the current conditions.

Different frequencies of ADCPs are suited for different water depths. In water of up to 70m, a good choice is the 600kHz ADCP. In such areas, where the depth does not exceed 110 meters, a better option would be the 300kHz. For deeper waters, such as areas exceeding 1000m found near Pohang, a 75kHz 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.