How can we measure the Coastal Currents of Kanoya?

1. Where is Kanoya?

Kanoya is a city in Kagoshima Prefecture on the island of Kyushu in Japan. It is a coastal city that lies on the East China Sea. The city has a rich history and is known for its connection to the sea.

Fishing, shipping, and all those maritime-related activities go towards supporting the local economy. The East China Sea surrounding Kanoya is rich as a marine environment. These host various fish species: tuna, mackerel, sardine, kelp, and shellfish bed seaweed. Its coast climate and marine environment is in the influence of warmth brought by the warm current, Kuroshio Current, with carried-down nutrients.

2. What is the condition of the coastal currents off Kanoya?

Many factors influence the coastal currents near Kanoya. Among all, the Kuroshio Current is predominant. This warm ocean current flows northward, bringing with it warm and nutrient-rich water that affects the marine fauna and the current itself in this area.

Tidal current bears significance too. Kanoya has a big tidal range, and with the inflow and outflow of water at every tide, it forms a very complicated current pattern. The shape of the coastline and the underwater topography are the main factors. Bays, headlands, and underwater ridges can make the currents change direction and speed. For example, the water flows faster around headlands and is deflected into bays. Besides, the wind pattern, especially in seasonal winds such as the winter monsoon, acts to drive the surface current and mix different layers of waters.

3. Observation of Coastal Water Flow

How to observe the flow of Kanoya coastal waters?

Surface Drifting Buoy Method: A buoy that can drift on the water surface is launched and used to observe the current on the surface. The movement of this buoy, over time, can be estimated using GPS or any tracking system. However, this procedure does have its drawbacks. All this will provide information with reference to the surface current itself, and it is often tampered with by strong wind and waves. Such phenomena can be exemplified as when a strong blowing of wind shifts the buoy sideways, against the direction where the actual current is taking the buoy.

Anchor-Boat Method: In this, an anchored boat is used for measurement. Instruments are lowered from the boat into the water to measure the current at different depths. While this allows for more detailed depth -wise measurements, it also has drawbacks. The fixed position of the boat restricts the area of measurement, and it may not capture the full variability of the currents in a large coastal area.

ADCP Method: The ADCP current meter method represents a more sophisticated and, at the same time, more efficient way of measuring the coastal currents. ADCPs send acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of the water at different depths. This gives a much fuller profile of the current right from the surface to the seabed. It also follows that ADCPs are less affected by surface disturbances and can operate without breaks over long periods, enabling an accurate picture of current structure.

4. How do ADCPs applying the principle of Doppler function?

ADCPs operate based on the Doppler effect. They emit high - frequency acoustic pulses into the water. When these pulses interact with moving water particles, the frequency of the reflected pulses changes. If the water particles are moving towards the ADCP profiler, the frequency of the reflected signal is higher than the emitted signal, and if they are moving away, it is lower.

The ADCP meter has a number of transducers that transmit and receive at several angles. It can measure the three-dimensional velocity with its analysis of Doppler shifts from different directions and from different depths. It means three-dimensional velocity would provide all horizontal and vertical components of velocity, offering an extremely useful insight into the structure and behavior of the current.

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

It should have reliable materials that ensure high-quality measurement of the coastal currents in Kanoya. A casing would be durable enough, with a salty base in water and possibly in storm conditions under the tide and oceanic current influence. The equipment should be of a compact size for its easy deployment and retrieval, taking into account the complicated landscape of coasts with bays and beaches.

A lightweight design is preferred since this makes the equipment more manageable during installation and maintenance. Low power consumption is necessary for long-term and autonomous operation. It should also be cost-effective for large-scale measurements.

It is also desirable that the casings be of titanium alloy. For seawater, titanium alloy serves with excellent corrosion resistance, is strong, and enduring in case of pressure variations of the water at different levels. This lightweight material is advantageous when considering various deployment options.

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

First, consider the purpose of use when choosing equipment for current measurement near Kanoya. If it is to be used for the navigation of a vessel or short-term research, then a ship-mounted ADCP flow meter would be suitable. It provides real-time current information during the voyage.

If the measurements are near the seabed, as for the study of sediment transport or benthic ecology, a bottom-mounted ADCP is better. The near-bottom current details can be captured. If the monitoring of the coastal current has to be done long-term and over a wide area, then a buoy-type ADCP current profiler is ideal.

Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP should be used. In depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters that might be found near Kanoya, such as areas with more than 1000m depth, 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.