How can we measure the Coastal Currents of Niigata?

1. Where is Niigata?

Niigata is a city located on the west coast of Honshu, Japan, facing the Sea of Japan. It's a major port city and is well - known for its rice production, heavy snowfall in winter, and vibrant local culture.

The local economy is diverse, with sectors such as shipping, manufacturing, and agriculture playing important roles. The Sea of Japan near Niigata is a rich fishing ground, home to a variety of fish like cod, herring, and squid. There are also extensive seaweed beds.

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

The coastal currents near Niigata are affected by a number of factors. Among the important ones is the Tsushima Current. This warm current, a branch from the Kuroshio Current, brings in warm water and nutrients. That in turn affects temperature and the distribution of marine life.

Another important factor involves tidal currents. The Sea of Japan has a considerable tidal range, and the ebb and flow of the tides lead to the formation of complex current patterns. The shape of the coastline and the underwater topography play a crucial role. The presence of bays, headlands, and underwater ridges can cause the currents to change direction and speed. Besides, the wind pattern, especially those seasonal winds blowing across the Sea of Japan, may drive the surface current and mix different layers.

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

Surface Drifting Buoy Method: A surface-drifting buoy can be thrown into the water for observing the surface current. The movement of the buoy is followed for a certain period with the help of GPS or other tracking systems. However, this technique does have its limitations. First, it provides information on the surface current alone and may be affected by wind and waves. For instance, when a strong wind blows the buoy in another direction than that of the current, it leads to the incorrect measurement of the direction and speed of the current.

Anchor - Boat Method: The current can be measured using an anchored boat. Instruments for measuring the current are lowered into the water from the boat at various depths. While this allows for more detailed depth - wise measurements, it also has its drawbacks. The boat's fixed position restricts the area of measurement, and it may not capture the full variability of the currents in a large coastal area.

ADCP is the more advanced and effective technique of measurement of coastal currents. ADCPs emit acoustic signals in water and measure the Doppler shift of the reflected signals to estimate the velocity of water at different depths. This gives a better profile of the current from the surface down to the seabed. Being less affected by surface disturbances, ADCPs can operate continuously over long periods and give a much better picture of the current structure.

4. How does an ADCP using the Doppler principle work?

ADCPs work on the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. As the pulses interact with moving water particles, the frequency of the reflected pulses becomes altered. If the water particles are moving toward the ADCP, then the frequency of the reflected signal is higher than the one emitted, while in the case of movement away, it becomes lower.

Various transducers of the ADCP radiate signals at different angles to obtain and return signals, their analysis, according to Doppler shift in different directions at various depths, allows one device to determine the three-dimensional velocity of water. The obtained velocity is three-dimensional and has horizontal and vertical components of this velocity, fully depicting the structure and behavior of the current.

5. What is necessary to make high-quality measurement of the Niigata coast current possible?

The equipment should be made of reliable materials to provide high-quality measurement of the coastal currents near Niigata. Since it is in a marine environment, with saltwater, possible exposure to storms, and the influence of tides and ocean currents, a durable casing is required. The size of the equipment should be small for easy deployment and retrieval, especially in such a complex coastal landscape with bays and headlands.

A lightweight design is preferred, as the equipment will be more manageable while installing and performing maintenance. It should have low power consumption in order to operate for long periods of time autonomously. Cost-effectiveness is also an important factor to realize large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. The reason is that the titanium alloy has excellent corrosion resistance, which is very important for fighting against the corrosive action of sea water. Besides, it is strong enough to bear the pressure of the water at different levels. Light in weight, it offers more convenience for various deployment methods.

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

For current measurement, near Niigata, selecting the equipment should consider the purposes of its use first. According to this, in order to decide on vessel navigation and/or short-term research, it would be advisable to adapt a ship-mounted ADCP, as it gives very valuable real-time current information in this 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.

Frequency-Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP is appropriate. For depths up to 110m, a 300kHz ADCP is more appropriate. For deeper waters that might be found near Niigata, 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.