How to measure the Coastal Currents of Kagoshima ?

1. Where is Kagoshima?

Kagoshima city is a part of Japan, and it is positioned at the southern tip of the Kyushu Island that is bordering the East China Sea and the Pacific Ocean. This city is recognized by volcanic landscapes, in particular being close to Sakurajima volcano, which is highly active.

The local economy is varied; fishing, shipping, and tourism are mainstays. The offshore waters are highly productive. In the East China Sea and the Pacific Ocean off Kagoshima, there is a wide variety of fish species, such as tuna, bonito, and mackerel. Extensive beds of seaweed and shellfish abound. The warm Kuroshio Current plays a very significant role in the local climate and marine ecosystem through its contribution of warm water and nutrient input.

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

Coastal currents in the vicinity of Kagoshima depend on a lot of factors. The main is, of course, the Kuroshio Current. This warm, north-flowing current has widespread effects in this region. The Kuroshio Current has wide effects on water temperature distribution and nutrients, marine organisms' distribution, as well as on fisheries management in general.

Another factor is tidal current. Kagoshima has a big tidal range, and the rise and fall of the tides create a complex current pattern. The shape of the coastline and underwater topography are important, too. Bays, headlands, and underwater ridges can make the currents change direction and speed. For instance, the water may flow faster around headlands and be deflected into bays. Besides, the wind regimes, particularly the seasonal winds, can push on surface currents and mix different water layers.

3. Observe the Coastal Water Flow from Kagoshima

Surface Drifting Buoy: By using a surface - drifting buoy, the latter will be released into the water and observe the surface current. Further, its movement can then be traced over time based on GPS or other position-detecting systems. However, this technique does have its own limitations. First, it gives only the surface current, and wind and waves may affect the result. For instance, when a strong wind blows the buoy in a direction other than that of the current, this may lead to a wrong measurement of direction and speed of the current.

Anchor - Boat Method: The current can be measured by an anchored boat. Instruments for the measurement of current are lowered from the boat into the water at different depths. Although this provides more detailed depth - wise measurements, it also has disadvantages. Because the boat is in a fixed position, only a small area of the total coastal area can be measured, and the variability in the currents over a large coastal area may not be represented.

ADCP Method: More advanced and efficient is the ADCP current meter method of measuring coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of the water at different depths. Thus, it gives a far more comprehensive profile of the current from the surface down to the seabed. Because ADCPs are less affected by surface disturbances, they can provide a continuous record over long periods and thus a truer representation of the current structure.

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. As these pulses encounter moving particles of water, their frequency changes due to interaction with the particles. In other words, if the particles are moving towards the ADCP profiler, the reflected signal frequency will be higher than the emitted frequency; if they are moving away, it will be lower.

The ADCP meter has several transducers that send and receive signals at different angles. Through the analysis of the Doppler shifts from different directions and at different depths, the device is able to calculate the three-dimensional velocity of the water. This means it can determine the horizontal and vertical components of the velocity, thus providing a detailed understanding of the current's structure and behavior.

5. What is required for the high-value measurement of Kagoshima coastal currents?

The equipment should also be made of reliable material for high-quality measurement of the coastal currents around Kagoshima. Since it is set in a marine environment and exposed to saltwater, storms, tides, and ocean currents, this calls for a casing that is durable. The size of the equipment should be small for easy deployment and retrieval, especially taking into consideration the complex coastal landscapes with bays and beaches.

A lightweight design is desirable for better manageability during installation and maintenance. It should have low power consumption in order to operate for a long time autonomously. Cost-effectiveness is also an issue in order to enable wide-scale measurements.

The housing for ADCPs is preferred to be made of Titanium alloy. The corrosion resistance of titanium alloy is excellent, which is critical for the corrosive actions by seawater. It is also strong enough and durable to bear the pressure at higher or lower depths of the water body. Its light weight factor provides more convenience with different deployment methods.

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

When selecting instruments to measure currents near Kagoshima, first think of the purpose of their use. If it is a vessel's navigation or a short-term research, the suitable instrument would be a ship-mounted ADCP flow meter. During a voyage, it will present current information in real time.

For measurements near the seabed, such as for studying sediment transport or benthic ecology, a bottom - mounted ADCP current profiler 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.

Frequency of ADCPs: For water depths up to 70m, a 600kHz ADCP is a good choice. In the case of up to 110m, a 300kHz ADCP would be more appropriate, while for deeper waters that may be found near Kagoshima-exceeding 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.