How can we measure the Coastal Currents of Hirosaki?

1. Where is Hirosaki?

Hirosaki is a city in Aomori Prefecture, located in the northern part of Honshu, Japan. It's near the Tsugaru Strait and the Sea of Japan. The city is famous for its historical Hirosaki Castle and beautiful cherry blossoms.

Local economy encompasses such fields as agriculture, fishing, and tourism. Rich marine resources are found within the coastal waters, most especially around the Tsugaru Strait and the Sea of Japan. These include fish such as salmon, herring, and shellfish. In addition, the climate and marine life of the area are affected by ocean currents, which include the Tsugaru Warm Current.

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

Various factors act upon the coastal currents around Hirosaki. The Tsugaru Warm Current is one of the most important. Relatively warm water and nutrients are brought in, influencing the temperature and distribution of marine life in the area.

The tidal currents are also significant. The Sea of Japan and the Tsugaru Strait have a great tidal range. The ebb and flow of the tides lead to the formation of complex current patterns. Shape of coastline and underwater topography are important. Bays, headlands, and underwater ridges may alter the direction and speed of currents. Besides, the wind pattern, particularly the seasonal wind blowing across the strait and the sea, can drive surface currents and influence the mixing of different layers.

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

Surface Drifting Buoy Method

A surface drifting buoy can be deployed in the water to measure the surface current. The buoy may be tracked over a measured period of time using Global Positioning System or other tracking methods. However, this method has its drawbacks. It only gives information on the surface current and may be interfered with by wind and waves. For instance, if a strong wind blows the buoy in another direction from that of the actual current, then it leads to incorrect measurements of the direction and speed of the current.

Anchor - Boat Method

The current can be measured using an anchored boat. Instruments to measure current are lowered from the boat into the water at depth. Whereas this permits more detailed depth - wise measurements, this also has its disadvantages. 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.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP method is an advanced and efficient way to measure the coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity of water at different depths. This provides a more comprehensive profile of the current from the surface to the seabed. Generally, ADCPs are less affected by surface disturbances and can work for continuous long periods with greater accuracy on the current structure.

4. How do ADCPs using the principle of Doppler work?

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

Correspondingly, the ADCP is equipped with multiple transducers that send and receive signals at different angles. In this way, it makes calculations of the Doppler shifts from different directions at different depths possible, hence yielding a three-dimensional velocity of water-that is, horizontal and vertical components of the velocity are identified for a thorough explanation of the structure and behavior of the current.

5. What is needed for high-quality measurement of Hirosaki coastal currents?

The equipment should be manufactured from reliable materials for high-quality measurements of the coastal currents around Hirosaki. The apparatus needs to be of robust casing, considering the salinity of the water, storms it may be exposed to, tides, and ocean currents. The size of the equipment should be small to be deployed and retrieved with convenience, especially in a highly complex coastal landscape with bays and headlands.

A lightweight design is preferable, as it makes the equipment more manageable at the time of installation and maintenance. Low power consumption is necessary for long - term and autonomous operation. Cost - effectiveness is also important for large-scale measurements.

The casing of ADCPs would be of titanium alloy. Titanium alloy has a very good resistance to corrosion, which is essential when working in seawater to avoid the corrosive nature of seawater. It is tough and durable to bear the water pressure at different levels of depth. Its lightweight is also advantageous for various deployment techniques.

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

Thus, to begin, use and identification should be the first one on which all equipment choices will be considered for current measurement around Hirosaki. Whenever these are needed for the purpose of vessel navigation or just some short-term research, ship-mounted ADCPs will be fine; while navigating, they provide on-the-spot information about current.

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.

Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP is a good choice. For depths up to 110m, a 300kHz ADCP is more appropriate. And for deeper waters that might be found near Hirosaki, such as areas with a depth exceeding 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.