How to measure the coastal currents of Yangjiang?

1. Where is Yangjiang?

Yangjiang City, located in the southwest of Guangdong Province in China, is a beautiful city with a pleasant natural environment and abundant cultural deposits.

Located in the coasts of the South China Sea, the city of Yangjiang is favored with beautiful beaches, crystal-clear waters, and a mild climate. It is bounded on the east by beautiful mountains and rich plains; the elevation foils in varicolored landscape invites every beholder's inspiration.

Yangjiang is popularly known for its particular local culture, which is a mixture of traditional Chinese elements along with maritime influences. The people of Yangjiang are warm and friendly; thus, they take pride in their city's history and traditions.

The waters bordering Yangjiang include the South China Sea and the Beibu Gulf. It is here that much marine life can be found, and in addition, these waters are important for fishing, shipping, and tourism.

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

The general features of the coastal currents near Yangjiang are the results of many factors that interact in a very complicated way to give this particular marine environment its characteristics.

One is the monsoon. The winds of the monsoon come from another direction each half of the year, and this reflection determines the direction and strength of the currents: the summer monsoon comes from southwest, pushes the surface waters towards the northeast, while the winter monsoon blows from northeast, with results that are completely opposite.

Another factor is topography of the seabed. Oceans with shapes, depth, and shelves determine how currents will flow, leading to areas of eddies and whirlpools. Around Yangjiang, there are areas of shallow waters and areas with deep trenches, hence variation in speeds and direction.

The other important element is tides. Because of the rising and falling of the tides, the constantly changing water levels create a circulating current-a so-called tidal current-that gives way to the movement of water alongshore. Sometimes interaction between those tides and monsoon winds further complicates the pattern of current.

Besides, the temperature and salinity of the water may alter the general local currents. Changes in temperature and salinity imply variations in the density of the water, and further implications for current flow-it can be altered or even nullified. Off Yangjiang, warm waters from the South China Sea and relatively cooler waters from Beibu Gulf can easily lead to a density gradient that could affect the direction and magnitude of the currents.

3. How to observe the current of Yangjiang coastal water?

Measuring the coastal water flow of Yangjiang is indispensable in understanding the marine environment for navigation, fishing, and environmental protection. Traditional approaches, using drift bottles, current meters, and satellite imagery, have been tried for the measurement of velocity and direction of currents. However, most traditional methods have significant limitations with regard to accuracy and spatial coverage.

The ADCP current profiler are more updated and convenient in measuring the currents of the coast and have been available for the last few years. In accordance with their nature, ADCP doppler use the principle of Doppler to measure the velocity of water flow in various layers of the water column all at once. In this way, more information becomes available for obtaining the most accurate current patterns possible.

3.1 How do Principle of Doppler-based ADCP Work?

Basically, Acoustic Doppler Current Profiler(ADCP) operate by sending out sound waves into the water and measuring the frequency shift of the reflected waves. The frequency shift is due to the motion of the water particles related to the velocity of the water flow. Through the analysis of the frequency shift, ADCP are able to determine the velocity of the water flow in a different direction.

Basically, ADCP current meter consist of a transducer array that sends out and receives sound waves. The transducer array is usually mounted on a ship, mooring, or buoy. Because of the movement of the water, the sound waves are reflected by the particles of water and received back through the transducer array. These received signals are further processed in a computer for velocity calculation of the flow of water.

3.2 What is required for high-quality measurement of Yangjiang coastal currents?

In the measurement of Yangjiang coastal currents, several factors will have to be considered in arriving at a high-quality measurement. First is the reliability of the equipment; the ADCP flow meter that are to be used in measuring the current should be made of durable materials that can withstand harsh conditions in the sea.

A number of other advantages make the titanium alloy an ideal material to work with in ADCP casings. First, it is highly resistant to corrosion by saltwater and other elements, making it suitable to fit within marine environments. It is also of strength-to-weight, easing the handling and installation process. Besides, the thermal expansion coefficient of titanium alloy is small enough to ensure measurement accuracy even under extreme temperature conditions.

In addition to material reliability, other factors such as size, weight, power consumption, and cost have also to be considered. In large-scale measurements, it is desired that ADCP meter be small in size and light in weight, so that their deployment and retrieval can be easily done. Low power consumption is also of prime importance, since this allows for longer battery life and reduces frequent recharging. Besides, cost decides the feasibility of large-scale deployment.

3.3 How to Choose the right equipment for current measurement?

Selection for the right equipment in Yangjiang will be based on several aspects. The first factor is the intended use of the equipment. Different applications call for varied ADCP types:. These are suited for the measurement of currents when the ship is in motion, whereas in the case of current monitoring over longer periods of time at a fixed location, bottom-mounted ADCP are suitable. Currents in areas inaccessible to other types of equipment can be measured using buoy-mounted ADCP.

Another important factor is the ADCP frequency. The rest of the frequencies are suitable for various water depths. For instance, 600 kHz ADCP are suitable for water depths up to 70 meters. 300 kHz ADCP are fit for water depths up to 110 meters, while 75 kHz ADCP are suitable for deeper waters of up to 1000 meters.

There are quite a few brands on the market for ADCP, including Teledyne RDI, Nortek, Sontek, and China Sonar. Of these, China Sonar's PandaADCP offers the best mix of quality and price. The PandaADCP uses all-titanium alloy material for excellent durability and corrosion resistance. Moreover, it has various frequencies for different water depth ranges. More information is given at https://china-sonar.com/.

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