How do we measure the Coastal Currents of Kobe?

1. Location of Kobe

Kobe is a bustling port city in the Hyogo Prefecture on the southern side of Honshu Island in Japan, with its shores along the Seto Inland Sea and an active history in international trade and maritime dealings.

Its strategic coastal location made this city an important economic hub of the country. It has an extended and busy port dealing in a variety of cargos such as automobiles, electronics, and other consumer goods. On the coastline, some beautiful parks, beaches, and marinas can also be found. Shipping, manufacturing, trade, and tourism are the sources by which the local people earn a living.

Off the shore of Kobe lies the Seto Inland Sea, a semiclosed sea with abundant life beneath. Some of the fish resources present within the sea include yellowtail, sea bream, and mackerel; there are also a few expanses of seaweed and shellfish. It ameliorates the climate greatly, regulating the temperatures to their present level and is climatically important.

2. What is the condition of the coastal currents off Kobe?

The coastal currents off Kobe are determined by several factors. Tidal currents are one of the most prevailing factors. The Seto Inland Sea has a considerable tidal range, and due to the rise and fall of the tides, complex current patterns are formed. The water flows in and out of the bays and channels around Kobe, creating a dynamic flow.

Another crucial role is played by the form of the coastline and the underwater relief. The facilities of the port with breakwaters and underwater shoals make currents change direction and speed. For instance, the water slows down while approaching a breakwater and speeds up while passing through a narrow channel. The inflow of freshwater from local rivers and canals can affect the salinity and density of the coastal waters, which in turn influences the current flow. In addition, the wind pattern-the seasonal winds blowing across the Seto Inland Sea-can drive surface currents and affect the mixing of different layers of water.

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

Surface-drifting buoy technique: A surface-drifting buoy may be used to observe the current from the water surface. This is observed over some time using a Global Positioning System - GPS and other tracking systems. Notwithstanding, the method presents a number of limitations; it can only give the surface current characteristics and sometimes is influenced by wind and waves. For instance, if a strong wind blows the buoy in a different direction from the actual current, it can lead to inaccurate measurements of the current's direction and speed.

Anchor - Boat Method: The current can also be determined by an anchored boat. In this case, the instruments that will measure the current are lowered from the anchored boat to the water. While with this method it is also possible to perform more precise depth-wise measurements, its disadvantages are the limitation of its area of measurement-the boat does not move much-and large coastal areas are difficult to measure for variability in the currents.

ADCP Method: The ADCP current meter method is more advanced and effective in measuring the coastal current. 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 right from the surface to the seabed. ADCPs are less affected by surface disturbances and can operate continuously for longer, giving a much more realistic view of the current structure.

4. How does an ADCP making use of the Doppler principle work?

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 profiler, the frequency of the reflected signal is higher than the emitted one; if they are moving away, it is lower.

Indeed, several transducers fitted within the ADCP meter transmit and receive signals through many aspects. It can deduce the three-dimensional velocities by analyzing Doppler shifts coming from various directions at depth. The device hence could provide information on both the horizontal and vertical components of the velocities, availing critical details in understanding structure and behavior.

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

The equipment for high-quality measurement of the coastal currents near Kobe should be made of reliable materials. A durable casing will be required, considering the marine environment with saltwater, possible exposure to storms, and the influence of tides and port activities. The size of the equipment should be small to allow for easy deployment and retrieval, especially in such a complex coastal landscape with its ports, breakwaters, and beaches.

A 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 vital for withstanding the corrosive effects of seawater. Besides, 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?

Equipment selection should first take into consideration the use to which it is meant to serve near Kobe. Vessel navigation and/or short-term research are considered under the use of a ship-mounted ADCP flow meter, since it will perform its current measurement in real time as the voyage progresses.

If the measurement is to be taken from near the seabed for the study of sediment transport or benthic ecology, a bottom-mounted ADCP is preferable. The instrument can capture the details of the near-bottom current. For long-term and wide-area monitoring of coastal current, a buoy-type ADCP current profiler is ideal.

For the frequency of ADCPs, in water as deep as 70m, a 600kHz ADCP will suffice. If the water is as deep as 110m, then a 300kHz ADCP is better suited. And for deeper waters that may be found around Kobe-like areas with a depth over 1000m, a 75kHz ADCP is suitable.

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.