How to Quantify Coastal Currents of Nagoya?

1. Location of Nagoya

Nagoya is a principal city of Aichi Prefecture, in central Honshu, Japan. Nagoya lies on Ise Bay, which is an inlet of the Pacific Ocean. It is one of the largest industrial and transport centers in Japan.

The city is a very important part of the economic infrastructure, as its port in Ise Bay promotes trade and shipping. The local economy is well diversified, ranging from a strong manufacturing base to trade, logistics, and some tourism. The bay is also a source of marine resources, with fish species like sea bream, mackerel, and yellowtail present. There are also seaweed beds and shellfish.

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

Multiple factors can influence the coastal currents in the vicinity of Nagoya. Tidal currents are well felt. Ise Bay has an average tidal range, where currents develop due to the process of inflow and outflow during tides. The shapes of the coastline and seafloor topography come into effect. The bay, channel openings, and underwater shoals cause disturbances in the direction and velocity of the currents.

The freshwater input from the rivers and other sources lowers the salinity and density of the coastal waters, which again has an effect on the current flow. Besides, the wind pattern, especially the seasonal winds across Ise Bay and the Pacific Ocean, may also drive surface currents and may cause mixing of different layers of water.

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

Surface Drifting Buoy Method: In this method, the surface-drifting buoy can be thrown into the water in order to view the surface current. Further, the movement of this buoy is traced for a time frame with the use of GPS or other tracking systems. This technique has its limitations, though. It can just account for the surface current and can be influenced by wind and waves. For instance, if strong winds break the buoy apart in a different direction, this would reflect incorrect measurements of direction and speed of the current.

Anchor-Boat Method: In this, the current is measured by an anchored boat. Instruments to measure current that are suspended from the boat at different depths in the water. This allows more detailed depthwise measurements; however, it suffers from some disadvantages. The area over which measurement can be made is limited by the fixed position of the boat and thus may not represent the entire variability in a large coastal area.

Acoustic Doppler Current Profiler Method: This is relatively advanced and a more productive means of measurement of coastal currents. ADCPs emit their acoustic signals into the water, and from the reflected signals, their Doppler shift determines the various velocities of water at different layers, thus offering a profound profile of the current between the surface and the sea bed. These have a lesser effect from surface disturbances and can run continuously for longer periods, thus giving a more accurate picture of the current structure.

4. How do ADCPs using the Doppler principle work?

The operating principle of ADCPs relies on the Doppler effect. ADCPs transmit high-frequency acoustic pulses through the water. Whenever the pulses reach the moving particles in the water, the frequency changes of the reflected pulses is varied. When the particles are moving toward the sonar, then it gives a higher frequency reflection compared to the emitted; otherwise, it reflects with a lower frequency.

ADCP current profiler has several transducers operating at different angles and performing tasks of sending and receiving signals. Thus, by analyzing the Doppler shifts from different directions and at different depths, this device will be able to calculate three-dimensional velocity. It would also be able to deduce the horizontal and vertical components of the velocity, which helps to provide a detailed view of the current structure and behavior.

5. What is required for a high-quality measurement of Nagoya coastal currents?

For high-quality measurement of the coastal currents near Nagoya, the equipment should have reliable materials. Given the marine environment, with saltwater, potential exposure to storms, and the influence of tides and the characteristics of Ise Bay, a durable casing is required. The size of the equipment should be small in order to facilitate easy deployment and retrieval, especially considering the complex coastal landscape with its bay and channels.

The lightweight design in preference will make the manipulations of equipment easier in installation and maintenance. Low power consumption is a prime necessity to operate for long terms autonomously; cost-effectiveness, in turn, is helpful to carry on extensive measurements.

The casing of ADCPs is preferably made of titanium alloy. It has excellent corrosion resistance, which is vital in withstanding the corrosive effects of seawater. It is strong and durable to withstand 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?

According to the purpose of use, choose the equipment for current measurement near Nagoya. When the measurement is for a vessel's navigation or short-term research, a ship-mounted ADCP will be suitable. During the voyage, it provides current information in real time.

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.

Frequency-Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP would suffice, while for up to 110m, a 300kHz ADCP is suitable, and for deeper waters that may be found near Nagoya with areas over 1000m, a 75kHz ADCP is ideal.

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.