How to measure the Coastal Currents of Aomori?

1. Where is Aomori?

Aomori Prefecture is situated at the northernmost part of Honshu, Japan, bordering the Tsugaru Strait and the Pacific Ocean. The city of Aomori is its capital and a major port and transportation hub in the region.

The local economy is very diverse, with fishing, agriculture, and tourism being some of the major sectors. Marine resources abound in the coastal waters, including salmon, herring, and several species of shellfish. The Tsugaru Warm Current also affects the area, carrying relatively warm water and nutrients into the region, thus influencing the local marine ecosystem and climate.

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

A variety of driving elements determine the structure of coastal currents in proximity to Aomori: the Tsugaru Warm Current, a most critical one, which advances across the Tsugaru Strait along a coastline, carries warm waters together with nutrients that already provide the impact on marine temperatures and life distribution.

The tidal currents are the following ones. The area 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 regime, especially the seasonal winds that cross over the strait and the ocean, can push surface currents and mix different layers of water.

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

Surface Drifting Buoy Method

The surface drifting buoy is used by releasing it into the water for observing the surface current. The movement of this buoy is followed for some period using GPS or any other tracking system. However, this method has its drawbacks. It can only give information about the surface current, and it may be influenced by wind and waves. For instance, if a strong wind blows the buoy in a different direction from the actual current, this may lead to erroneous measurement of the direction and speed of the current.

Anchor - Boat Method

This can be done by an anchored boat. 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.

Acoustic Doppler Current Profiler(ADCP) Method

The ADCP is a relatively newer and most efficient means of estimating the coastal currents. ADCPs emit acoustic signals into the water and measure the Doppler shift of the reflected signals to calculate the velocity at various water depths.

This provides a more comprehensive profile of the current from the surface to the seabed. ADCPs are less affected by surface disturbances and can operate continuously for long periods, giving a more accurate picture of the current structure.

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

The operation of ADCPs depends on the Doppler Effect. They emit high-frequency 'acoustic pulses' in the water. If there are moving water particles interacting with those pulses, the frequency of the reflected pulses becomes different. If the moving water particles are towards the moving ADCP, the reflected signal frequency is higher than that which is emitted, while for others that move away, it becomes lower.

The ADCP has several transducers, which transmit and receive signals at various angles. By analyzing the Doppler shifts from different directions and at different depths, the device can calculate the three-dimensional velocity of the water. This means it can determine the horizontal and vertical components of the velocity, providing a detailed understanding of the current's structure and behavior.

5. What is required for good measurement of Aomori coastal currents?

For high - quality measurement of the coastal currents near Aomori, the equipment should be constructed with reliable materials. With an environment like the sea-exposure to saltwater, potential storms, tides, and ocean currents-a hardy casing is needed. The size of the equipment should be small, enabling it to be set up and retrieved easily with the complicated topography of the coastlines: bays and headlands.

A lightweight design is preferred because it makes the equipment more manageable during installation and maintenance. Low power consumption is required for long - term and autonomous operation. Cost - effectiveness is likewise necessary to allow large-scale measurements.

The casing of ADCPs is preferably made of titanium alloy. Titanium alloy has excellent corrosion resistance, which is essential for withstanding the corrosive effects of seawater. It is strong and durable to bear the pressure of 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?

The equipment for current measurement near Aomori should be chosen according to the purpose of use. For the vessel's navigation or short-term research, a ship-mounted ADCP would be suitable. It can provide real-time current information during the voyage.

The measurements that concern the seabed, such as for the study of sediment transport or benthic ecology, require a bottom-mounted ADCP. In this respect, it will catch the detail of the near-bottom current. In case the monitoring of coastal current concerns long-term and wide area, a buoy-type ADCP is ideal.

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