How can we measure the coastal currents of Longkou?

1. Where is Longkou?

Longkou is one of the coastal cities in Shandong Province, China. It is located along the northern coast of the Shandong Peninsula, bordering the Bohai Sea. The city has highly developed ports and a flourishing economy in shipping, fishing, and manufacturing industries.

Longkou has been classified as a warm-temperate monsoon climate. It has a relative mild winter and warm summer. As the sea breeze plays a role in modification, the general condition is pleasant enough to live there. The rainfall is fairly moderate, which supports various vegetations, ranging from coastal forests to agricultural crops.

It is rich in maritime backgrounds, and the fishing traditions were rooted here. The development of the city has many relations to the sea. The seabed topography off Longkou is made up of shallow to deeper waters, aside from the other underwater features that consist of shoals and troughs.

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

Various factors influence the form of the coastal currents close to Longkou. First, there is a monsoon climate: during summer, a southeast monsoon may displace the surface waters and determine the direction and speed of the coastal currents, which can affect fishing and shipping activities. During winter, the current pattern is altered by the northwest monsoon, which usually produces different flow directions and speeds.

Then, there is topography: arguably an even more important factor. Underwater ridges, troughs, and shoals can route the water in various directions and at various speeds. Where shallow areas exist, currents tend to be slower, while stronger, more complex flows take place in deeper regions. The shallowness of the water may slow it down, for example; or in troughs, the current can be more vigorous with a more complicated type of circulation.

Another important factor is tide. The Bohai Sea can generally experience great tidal currents due to its regular ebb and flow. Especially near estuaries and narrow channels, these tidal currents can be strong. They form a very important medium for the transportation of sediments, nutrients, and marine organisms. Tidal currents create influences on erosion and sediment deposition in coasts that may lead to changing shapes in coastline and change distribution areas in marine life.

In addition, the interaction with the larger-scale ocean currents from the Bohai Sea and other adjacent regions can further modify the coastal currents in the vicinity of Longkou. These oceanic currents have the capacity to introduce water masses with different temperatures and salinity, which would further influence local current dynamics. For instance, intrusion of warmer or colder water masses can lead to a temperature shift in the coastal waters, perhaps impacting the local marine ecosystem.

3. How to Observe Longkou Coastal Water Flow?

Precise measurement of the coastal currents in Longkou is an indispensable means for marine safety, fishery management, and coastal protection. Generally, observation of coastal water flow has been performed by buoys and current meters. However, these conventional methods have various limitations regarding their precision and coverage.

Recently, ADCP profiler ​have become more advanced and convenient for the measurement of coastal currents. The principle of velocity measurement in ADCP meter is based on the Doppler principle.

3.1 Working of the Acoustic Doppler Current Profiler(ADCP) using the Doppler principle

ADCP flow meter emit sound waves into the water. These emitted waves interact with the moving particles in the water, such as suspended sediments and small organisms. Due to the motion of the particles, reflected sound waves change in frequency. This shift in frequency has a relationship to the velocity of the water current.

The transducer array of ADCP doppler sends and receives sound waves in various directions. The frequency shifts of the reflected waves in multi-directions are used by ADCP current profiler to calculate the current speed and its direction at different depths. This makes it possible to obtain the three-dimensional structure of the current.

3.2 What is required for high-quality measurement of the currents off the coast of Longkou?

With regards to the fine measurement of the coastal currents in Longkou, a number of conditions ought to be put into consideration. First and foremost, the equipment ought to be highly reliable. The ADCP current meter ought to be made from materials that are able to bear up against the harsh marine conditions.

Titanium alloy has proved to be one of the best materials to make the casing of acoustic doppler velocity meter due to its high resistance to corrosion especially in salt water at the coast. It is resistant to the corrosion effects of seawater and marine organisms for long life service of the equipment. The titanium alloy is also strong yet lightweight. Its strength enables it to withstand the physical stresses in the ocean, while light weight enables it to be handled and installed with ease.

Besides material reliability, other characteristics such as compact size, lightweight, low power consumption, and low cost become very useful. The nature of compact and lightweight ADCP is easy to carry and install at the site for taking measurements in places that would otherwise have become inaccessible. Low power consumption enables it to run longer without the need to change batteries frequently or make use of high-capacity power. Cost-effectiveness is vital for large-scale deployment to monitor the coastal area more intensively.

3.3 How to choose the right equipment for current measurement?

In choosing the right equipment to measure the coastal currents in Longkou, various factors are put into consideration. The intended application of the equipment is an outstanding factor.

An ADCP mounted on a ship can serve for measurements from an underway vessel. In this case, it could provide current in real time while the vessel is moving along the coast, hence enabling one to continuously monitor current conditions.

If measurements need to be undertaken at a fixed position on the seabed, then the bottom-mounted ADCP is the correct choice. It can be installed in a certain position and provide long-term stable measurements of current in that particular position.

The buoy-mounted ADCP can be utilized in open water or where installation by fixed platform is not feasible. In the currents measured can be larger area and data transmitted wirelessly.

About the frequency, different frequencies suit different water depths. In waters less than 70 meters, a 600 kHz ADCP is generally proper. For waters from 70 to 110 meters, the best is a 300 kHz ADCP. An ADCP of 75 kHz should be used in case of those waters reaching as much as 1000 meters.

When it comes to choosing an ADCP brand, well - known international brands such as Teledyne RDI, Nortek, and Sontek are popular options. However, for those seeking a cost - effective yet high - quality alternative, the ChinaSonar PandaADCP is worth considering. Made entirely of titanium alloy, it combines durability and reliability with an excellent price - performance ratio. You can find more information about it at https://china-sonar.com.

Here is a table with some well known ADCP instrument brands and models.