How to measure the Coastal Currents of Hachinohe?

1. Where is Hachinohe?

Hachinohe is a city in Aomori Prefecture, on the northeastern coast of Honshu, Japan. It is a major port city and is well-known for its fishing industry as well as for the beautiful scenery of its coasts.

The local economy is deeply dependent on fishing, aquaculture, and related industries. In the Pacific Ocean around Hachinohe, many marine resources abound, such as tuna, salmon, and a variety of shellfish. The area is also influenced by the Tsugaru Warm Current, which brings warm water and nutrients, enhancing the productivity of the marine ecosystem.

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

Its coast receives oceanic currents from various branches, with the Tsugaru Warm Current being another critical influence. This particular current is a warm and nutrient-rich water flow entering into this area. All such factors influence the current of sea temperatures that face the coasts of each of these cities, how living organisms are distributed at certain places, and typical pattern flows.

Tidal Currents: There is a certain tidal range around Hachinohe, and the ebb and flow of the tides develop into complex current patterns. In particular, the coastline and underwater topography are very important. The existence of bays, headlands, and submarine ridges can change the directions and speeds of the currents. Besides, the wind patterns, especially the seasonal winds like the trade winds, may push the surface currents and mix different layers of water.

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

Surface Drifting Buoy Method: A surface - drifting buoy can be released into the water to observe the surface current. The buoy's movement is tracked over time using GPS or other tracking systems. However, this method has a limitation, it gives only the surface current and can be affected by wind and waves. For instance, if a strong wind blew the buoy in a direction different from the actual current, it would result in incorrect measurement of the direction and speed of the current.

Anchor - Boat Method: Current can also be measured by an anchored boat. Instruments are lowered into the water from the anchored boat to measure the current at different depths. While this allows for more detailed depthwise measurements, it also presents some disadvantages. The fixed position of the boat restricts the area in which measurement can be performed, and it may not capture the full variability of the currents in a large coastal area.

The Acoustic Doppler Current Profiler (ADCP) method is an advanced and much more efficient way of measurement of 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 yields a much better 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 Doppler principle work?

ADCPs work on the principle of the Doppler effect. They shoot high-frequency acoustic pulses into the water. Whenever these pulses interact with moving particles of water, the frequency of the reflected pulses changes. If the movement of the water particles is towards the ADCP profiler, then the reflected signal frequency is higher than that emitted; if away, it is lower.

The ADCP meter has several transducers that transmit and receive at different angles. By analysing the Doppler shift from different directions and at a different depth, the instrument can calculate three-dimensional velocity; that is, horizontal and vertical components of the velocity could be defined, which, in turn, yields a detailed explanation of the structure and behavior of currents.

5. What is necessary for high-quality measurement in the currents of Hachinohe?

The equipment should be fabricated with materials that can reliably ensure high-quality measurement of the currents near Hachinohe. In light of a marine environment including saltwater, potential storms, tides, and ocean currents, the casing needs to be one that will be able to survive these rigors. Its size should be small, allowing easy deployment and retrieval, taking into account the complexities in landscape with bays and beaches.

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

The casing of ADCPs is preferably made of titanium alloy. It is basically for its excellent corrosion resistance, which is very much essential to resist the corrosive action of seawater. Besides this, it is strong enough and durable to bear the pressure of water at different depths, and its light weight makes it more handy for various deployment methods.

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

Equipment for current measurement at Hachinohe should be selected with consideration of the purpose of its use. In the case of a vessel navigating or short-term research, a ship-mounted ADCP flow meter is adequate. It will provide current information in real time during the voyage.

If measurements near the seabed, for example, for the study of sediment transport or benthic ecology, are needed, a bottom-mounted ADCP current profiler is better. It can capture the details of the near-bottom current. If long-term and wide-area monitoring of the coastal current is needed, the buoy-type ADCP is ideal.

Regarding the frequency of ADCPs, for the water depth up to 70m, a 600kHz ADCP will suffice. In areas where the water depth is up to 110m, a 300kHz ADCP would be more suitable. For deeper waters, which might be found near Hachinohe, such as areas with more than a 1000m depth, a 75kHz ADCP is recommended.

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.