How to measure the Coastal Currents of Fukuoka?

1. Where is Fukuoka?

Fukuoka is a dynamic city situated on the northern shore of Kyushu Island in Japan. It is a significant port city and an important economic and cultural center in the region. The city is bounded by the Genkai Sea, which is part of the larger East China Sea.

Fukuoka's landscape is a harmonious blend of urban development and natural beauty. The city center is filled with modern skyscrapers, bustling shopping areas, and historical temples. The coastal areas, on the other hand, feature beautiful sandy beaches and marinas. The local population is engaged in a wide range of activities, including trade, fishing, and tourism.

The Genkai Sea offshore of Fukuoka represents a rich marine environment. In this body of water, there exists a great variety of fish species: mackerel, sardine, tuna, and so on. It provides wide seaweed and shellfish beds. The warm Kuroshio Current, the major ocean current in the region, largely influences the local climate and the marine ecosystem of the above area. Warm water with nutrient salts is carried by the current, adding to the high productivity of the sea.

2. What is the situation of coastal currents around Fukuoka?

The coastal currents around Fukuoka have been influenced by more than one factor. One of the dominant influences here is that of the Kuroshio Current. It is warm and flows northwards, with a wide-reaching impact on this particular area. It affects everything from the temperature of the water to the nutrient and marine life distribution.

Tidal currents play an important part, too. Fukuoka has a pretty high tidal range, and as the tides ebb and flow, complex current patterns emerge. The shape of the coastline and the underwater topography are crucial as well: bays, headlands, and underwater ridges can cause the currents to change direction and speed-for example, the water will flow faster around headlands and be deflected into bays. In addition, the wind patterns, particularly the seasonal winds like the winter monsoons, can push surface currents and contribute to the mixing of different layers of water.

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

Surface Drifting Buoy Method: A surface - drifting buoy can be released into the water to observe the surface current. The buoy's movement is tracked over time using GPS or other tracking systems. However, this method has its limitations. It only gives information about the surface current and is susceptible to wind and waves. For instance, if a strong wind blows the buoy in a different direction from the actual current, it can lead to incorrect measurements of the direction and speed of the current.

Anchor-Boat Method: An anchored boat can be utilized to measure the current. Instruments are lowered from it into the water to measure the current at different depths. This again, while allowing for more detailed depth-wise measurements, has its drawbacks. Its fixed position restricts the area of measurement, probably not fully representative of all the variabilities of the currents in a large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method: Being more technologically advanced, the ADCP method is in many respects far more competent in coastal current measurement. ADCPs emit an acoustic signal into the water and measure the Doppler shift of the reflected signal to obtain the velocity at different water depths. This indeed gives a much better view of the current profile right from the surface to the seabed. ADPCS are less affected by surface disturbances and can run continuously for a long period, hence providing a better picture of the structure of the current.

4. How does the ADCP applying the Doppler Principle work?

ADCPs work on the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. In this case, when the pulses meet moving water particles, their frequency is changed. If the water particles are moving towards the ADCP, the frequency of the reflected signal is higher than that emitted; if they are moving away, it is lower.

The ADCP is fitted with several transducers that broadcast and receive signals at differing angles. With the change in Doppler from several directions at varying depths, the device computes the three-dimensional velocity. It means this device computes both horizontal and vertical components of the velocity by providing the details of current structure and its behavior.

5. What is necessary for high-quality measurement of the Fukuoka coastal currents?

For high - quality measurement of the coastal currents near Fukuoka, the equipment should have reliable materials. Given the marine environment, with saltwater, potential exposure to storms, and the influence of tides and ocean currents, a durable casing is essential. The equipment's size should be small for easy deployment and retrieval, especially considering the complex coastal landscape with its bays and beaches.

A lightweight design is preferred since it makes the equipment easier to handle at the time of installation and maintenance. Low power consumption is essential for long - term and autonomous operation. Cost - effectiveness is also required for large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is very important for resisting the corrosive action of seawater. It is also strong and durable to bear the pressure of the 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, when choosing equipment for current measurement near Fukuoka, consider the purpose of use. If the measurement is for a vessel's navigation or short-term research, a ship-mounted ADCP is a suitable option. 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 since 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 the water depths up to 70m, a 600kHz ADCP will do. For depths up to 110m, a 300kHz ADCP is more appropriate, while for deeper waters that might be found near Fukuoka, 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.