How Can We measure Ishinomaki's coastal currents?

1. Where Is Ishinomaki?

Ishinomaki City is an important urban center of Miyagi Prefecture located on the east coast of Honshu Island in Japan, facing the open waters of the Pacific Ocean; thus, being a great catchment point for sea produce along its shoreline.

The local economy is very dependent on fishing and other related industries. The Pacific Ocean off Ishinomaki is rich in marine resources, such as all kinds of fish, including tuna, mackerel, and sardine, seaweed, and shellfish. The area is also influenced by the Kuroshio Current, which carries warm water and nutrients, enriching the productivity of the local marine ecosystem.

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

The coastal currents around Ishinomaki are dominated by several factors. This includes the Kuroshio Current, which is major. It is a warm, north-flowing ocean current that carries warm and nutrient-rich water. It regulates the temperature of the coastal waters and the distribution of marine life; it also regulates the general flow of currents.

Tidal currents also play an important role. Ishinomaki has its tidal range, and the ebbs and flows of the tides involve the formation of complex patterns of currents. The form of the coastline and submerged topography become the leading determinants. Bays, headlands, and underwater ridges will be more likely to change the direction and speed of the currents. Moreover, the wind patterns, particularly the seasonal winds like the trade winds, are able to push the surface currents and influence the mixing of different layers of water.

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

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 its limitations. It tells about the surface current alone and is prone to wind and waves. For instance, the buoy is blown by strong wind in some other direction other than that of the current; it will provide incorrect measurement in respect of the direction of the current and its speed.

Anchor - Boat Method

In this, the current is measured by an anchored boat. The instruments are lowered from the boat into the water to measure the current at different depths.

Although this allows more detailed depth - wise measurements, there is a major disadvantage in the fact that the boat occupies a fixed position, and its area of measurement may not allow the full variability of the currents in a large coastal area.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP method is comparatively more advanced and efficient ways 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. It thus delivers the finer details of the in-water current structure from surface to seabed. There is less interference on ADCPs from surface perturbations, and instruments can be deployed for extended periods with continuous operation, thus providing a truer representation of the current structure.

4. How Do the Doppler Principle ADCPs Work?

The working of ADCPs is based on the Doppler effect. They transmit high-frequency acoustic pulses into the water. As these pulses encounter and interact with the moving water particles, their frequency changes. If the water particles are moving towards the ADCP current meter, then the reflected signal frequency is higher than the emitted one; if they are moving away, it is lower.

Accordingly, the ADCP is fitted with several transducers that transmit and receive signals at different angles. The determination of the three-dimensional velocity of the water-that is, the horizontal and vertical components of the velocity-is obtained by analyzing the Doppler shifts from different directions and different depths. This will provide great detail on the structure and behavior of the current.

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

The equipment should be made of reliable materials for high-quality measurement of the coastal currents around Ishinomaki. A durable casing will be required because of the marine environment, with saltwater, potential exposure to storms, and the influence of tides and ocean currents. The size of the equipment should be small for easy deployment and retrieval, especially considering the complex coastal landscape with its bays and beaches.

A lightweight design is preferred because this renders the instrument easier to handle during both installation and maintenance. Low power consumption is another basic requirement due to longand autonomous operational conditions. Cost - effectiveness should also be high in order to enable large-scale measurement.

The casing of ADCPs is preferably made of titanium alloy. For this reason, titanium alloy boasts excellent corrosion resistance, which is very vital in withstanding the corrosive effects of sea water. It is strong and durable to bear such pressure of water at different levels. Its lightweight nature makes it more feasible for various deployment methods.

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

Equipment for current measurement at Ishinomaki shall be selected considering the purpose of use. Measurement for the navigation of a vessel or short-term research deserves a ship-mounted ADCP. It provides current information in real time during the voyage.

Bottom-mounted ADCP would be desirable in the case of measurements near the seabed, for instance for studying sediment transport or benthic ecology. The bottom-mounted one will capture the details of the near-bottom current. For the purpose of long-term and wide-area monitoring of coastal current, a buoy-type ADCP is ideal.

Frequency-Regarding the frequency of ADCPs, for water depths up to 70m, a 600kHz ADCP would be ideal. For such depths up to 110m, a 300kHz ADCP will be appropriate, while for deeper waters that may be found near Ishinomaki, say with depths of over 1000m, a 75kHz ADCP should be 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.