How can we measure the Coastal Currents of Kitakyushu?

1. Where is Kitakyushu?

Kitakyushu is a city in Fukuoka Prefecture, located at the northern tip of Kyushu Island in Japan. It is a coastal city that lies on the Seto Inland Sea and the Genkai Sea. The city is an important industrial and transportation hub.

The area around Kitakyushu features a combination of industrial zones, ports, and natural coastal landscapes. Large factories and steel mills show its industrial heritage. Along with the industrial areas, there are sandy beaches, rocky shores, and small islands. The local population is engaged in industries like manufacturing, shipping, and fishing.

The Seto Inland Sea and the Genkai Sea offer a rich environment for marine biota around Kitakyushu. The waters are inhabited by fish of many kinds, such as mackerel, sea bream, and anchovy; there are also large stocks of seaweed and other edible mollusks and crustaceans. A very important part is taken by sea currents in forming the local ecosystem and the climate of the region at all. The warm Kuroshio Current and the Tsushima Current influence the temperature and nutrients distribution around the area.

2. What is the state of the coastal currents off Kitakyushu?

The coastal currents off Kitakyushu are determined by several causes. First, there is the influence of the Kuroshio Current, a powerful warm ocean current, and the Tsushima Current. Warm water with nutrients is carried by these currents, thus influencing the local marine ecosystem and coastal currents.

Secondly, tidal currents are important. Kitakyushu has a large tidal range, and the inflow and outflow of water at each tide create very complicated current patterns. The shape of the coastline and underwater topography are very important. Bays, channels, and underwater ridges can make the currents change direction and speed. For instance, it can flow faster through narrow channels or be deflected by an underwater ridge. Besides, the wind pattern, especially the seasonal wind, might force the surface current and induce different layers of water to mix.

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

Surface Drifting Buoy Method: A surface -drifting buoy can be launched into the water for observing the surface current. With the help of a Global Positioning System or some other tracking device, one can trace the buoy for a considerable amount of time. There are some drawbacks to this approach. It gives information about the surface current only and can be influenced by wind and waves. For instance, if a strong wind blows the buoy in a different direction from the actual current, it results in erroneous measurements of the direction and speed of the current.

Anchor-Boat Method: An anchored boat can also be utilized for measuring current. The instruments to measure the current at various depths are lowered in water from the boat. In this method, the recordings of current in regard to depth are more detailed; on the other hand, there are a number of drawbacks too. This fixed position restricts the area of measurement; a large coastal area might have varying currents that could not be covered by an anchored boat.

Acoustic Doppler Current Profiler (ADCP) Method: The ADCP method is a more advanced and efficient way of measuring the coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of water at different depths. This provides a more comprehensive profile of the current from the surface to the seabed. These ADCPs are less prone to surface disturbances and can remain on continuously for long periods without deteriorating, thus reflecting more of the current structure realistically.

4. How do ADCPs Using the Doppler Principle Work?

ADCPs work on the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. Whenever these pulses encounter moving water particles, the frequency of the reflected pulses is changed. If the water particles are moving towards the ADCP, then the reflected signal frequency is higher than the emitted one; if they are moving away, it is lower.

The ADCP is equipped with several transducers, which send and receive signals at different 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 determine the horizontal and vertical components of the velocity, providing a detailed understanding of the current's structure and behavior.

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

For high-quality measurement of the coastal currents near Kitakyushu, the equipment should have reliable materials. In a marine environment, with saltwater, exposure to storms, and tides and currents, it has to be able to endure them all in a casing that is strong enough. Its size should be small to make its deployment and retrieval easy, especially when one considers the complex coast landscape with its bays, islands, and industrial areas.

A lightweight design is preferable as it makes the equipment more manageable during installation and maintenance. Low power consumption is important to make the operation possible for a long term and autonomously. Cost-effectiveness is also important in enabling large-scale measurements.

The casing of ADCPs is preferably to be made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is essential in fighting against the corrosive effect caused by seawater. It is also strong enough and durable to bear the water pressure at different levels. It is lightweight, thus easier in various deployment methods.

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

For equipment selection for current measurement around Kitakyushu, use shall be the primary consideration. When it is to be used for vessel navigation or short-term research, a ship-mounted ADCP shall be available. It will solve the problem of real-time information about the current 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 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 Kitakyushu, such as areas with a depth over 1000m, a 75kHz ADCP is recommended.

There are well - known ADCP 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.