How can we measure the Coastal Currents of Noshiro?

1. Where is Noshiro?

Noshiro is a city in Akita Prefecture, on the Sea of Japan side of Honshu. It is a coastal city with rich history and natural beauty. The local economy has diverse sectors such as fishing, agriculture, and light manufacturing.

The Sea of Japan near Noshiro is a resource area. Many kinds of fish such as cod, herring, and squid live there. There are also extensive seaweed beds. These provide a base for the local fishing industry, while the coastal area also has a port that participates in transportation and trade.

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

Multiple factors exert their influence on the coastal currents around Noshiro. One such influence is the Tsushima Current, a warm current branching from the Kuroshio Current; it transports warm water full of nutrients, influencing temperature and life distribution.

The tidal current is another influence. The Sea of Japan enjoys a large tidal range, with complex current patterns caused by the ebbs and flows of the tides. The shape of the coastline and underwater topography are responsible. Bays, headlands, and ridges underwater can easily result in changes of direction and speed. Besides, the wind pattern, particularly the seasonal wind crossing the Sea of Japan, may push the surface current and influence the mixing of different layers.

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

Surface Drifting Buoy Method

A surface drifting buoy can be deployed in water to study the surface current of the water. The movement of the buoy is followed over a certain period of time using GPS or other tracking systems. However, this technique does have some limitations. Firstly, it provides information of the surface current alone and, secondly, it can be interfered with by wind and waves. For instance, when the buoy is blown away from the real direction of current by strong wind, that can give incorrect readings regarding the direction and speed of the current.

Anchor - Boat Method

The current can also be measured by an anchored boat. Instruments are lowered from it in the water to measure the current with depth. While this method will allow for more depthwise detailed measurements, the procedure has disadvantages. Only a small area is left within which measurement can be performed with the boat in a fixed position, and the full variability of the currents over a large coastal area may not be captured.

ADCP Method

The ADCP current meter method is advanced and more efficient in the measurement of 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 gives a more complete profile of the current from surface to seabed. Since ADCPs are less susceptible to surface perturbance and can thus run uninterruptedly over longer lengths of time, they will be able to give much better records of the structure of the currents.

4. How do Doppler Principle-using ADCPs Work?

ADCPs work by the principle of the Doppler effect. They transmit high-frequency acoustic pulses into the water. As these pulses encounter the moving water particles, their reflected pulses change in frequency. If the water particles are moving towards the ADCP profiler, then the reflected signal frequency is higher than the emitted one; if they are moving away, it's lower.

Multiple transducers are installed on the ADCP meter, and they transmit and receive the signals at different angles. The device is able to calculate the three-dimensional velocity of the water by analysis of the Doppler shifts from different directions and depths. It can determine both horizontal and vertical components of the velocity.

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

The equipment should be manufactured from reliable materials for high-quality measurement of the coastal currents around Noshiro. In the marine environment, saltwater, potential exposure to storms, and the influence of tides and ocean currents require a casing to be durable. The equipment must be small in size because it is deployed and retrieved without a complex landscape of coast bays and headlands.

A lightweight design is preferable as it makes the equipment more manageable during installation and maintenance. Low power consumption is crucial for long - term and autonomous operation. Cost - effectiveness is also important to enable large - scale measurements.

The casing of the ADCPs is preferably of titanium alloy. Titanium alloys have superior corrosion resistance, which can resist the corrosive effect of seawater. Besides, it provides strength and toughness, it can resist the pressure coming from water of different deeps, and it is much lighter to handle in almost all kinds of deployment methodologies.

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

When choosing equipment for current measurement near Noshiro, considering the purpose of use shall be the first thing. For a vessel's navigation or short-term research, a ship-mounted ADCP flow meter would do. It provides real current information during the voyage 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 current profiler is ideal.

Frequency-Regarding the frequency of ADCPs, in water with a depth of up to 70m, a 600kHz ADCP is ideal. In depths up to 110m, one should go for a 300kHz ADCP. For deeper waters, which might be found near Noshiro, for example, areas with over 1000m in depth, a 75kHz ADCP will be better.

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.