How do We Measure the Coastal Currents of Matsuyama?

1. Where is Matsuyama?

Matsuyama City is on the island of Shikoku, in a country called Japan. It is a coastal city that faces the Seto Inland Sea. It features a hot spring Dogo Onsen dating back into history and Matsuyama Castle. Local culture abounds in the place.

The local economy is maintained with a combination of tourism, fishing, and some light manufacturing. The Seto Inland Sea off Matsuyama is a rich marine environment that provides a variety of fish species such as sea bream, mackerel, and sardines. There are also large sheets of seaweed and shellfish. The sea plays an important role in the local climate and provides livelihood from fishing and related industries to a large number of people.

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

There are a number of factors that affect the coastal currents near Matsuyama: tidal currents, for one, are a significant factor. The Seto Inland Sea has a moderate tidal range, and the ebb and flow of the tides lead to the formation of current patterns. The shape of the coastline and the underwater topography play a crucial role. The bays, channels, and shoals underwater make the currents change direction and speed.

The inflow of freshwater from rivers and other sources can influence the salinity and density of the coastal waters, which may influence the flow of current. Moreover, wind patterns, especially the seasonal winds that blow over the Seto Inland Sea, can drive surface currents and may affect mixing of different water layers.

3. How to Observe the Coastal Water Flow of Matsuyama?

Surface-Drifting Buoy Method: A buoy is let loose in the water to study the surface current. A GPS or other tracking systems track its motion over time. However, the drawback of this method is that it will give the current details of only the surface, which may be affected by wind and waves. For example, it could be that strong wind is blowing the buoy in a direction other than that of the actual current; hence, there are possible erroneous recordings of the current direction and speed.

Anchor-Boat Method: An anchored boat can be used to measure the current. 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 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 Method: The Acoustic Doppler Current Profiler (ADCP) method is a more advanced and efficient way of measuring 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. Being less affected by surface disturbances, ADCPs are instruments that can work for continuous operation over long periods and yield the current structure with greater certainty.

4. Working of ADCPs based on Doppler Principle

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

The ADCP current profiler has multiple transducers that send and receive signals at different 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 high-quality measurement of the Matsuyama coastal currents?

The equipment to be used for the measurement of the coastal currents near Matsuyama should be made with reliable materials. Considering a marine environment with saltwater, exposure to storms, tides, and characteristics of the Seto Inland Sea, it should have a durable casing. The size of the equipment should be small, enabling easy deployment and retrieval, taking into consideration the complex landscape of the coasts with bays and channels.

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

First, when choosing equipment for current measurement near Matsuyama, consider the purpose of use. If the measurement is for a vessel's navigation or short-term research, then a ship-mounted ADCP is suitable. It provides real-time current information during the 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.

For the frequency of ADCPs, in water as deep as 70m, a 600kHz ADCP should be used. For a depth up to 110m, a 300kHz ADCP should be applied. For deeper water, such as over 1000m, which could be around Matsuyama, a 75kHz ADCP is suggested.

There are well-known ADCP flow 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.