How can we measure the coastal currents of Taiwan?

1. Where is Taiwan?

Taiwan, officially known as the Republic of China (ROC), is an island in East Asia. It is located across the Taiwan Strait from the Chinese mainland. With an area of about 36,000 square kilometers, Taiwan is a wonderful and varied land.

Indeed, Taiwan is famous for its splendid natural scenery: towering mountains, including the renowned Yushan, the highest peak in Northeast Asia; lush, verdant forests; picturesque beaches; and hot springs. The climate varies from tropical in the south to subtropical in the north, providing a rich variety of flora and fauna.

Taiwan is a plural society, comprising many ethnic groups. The first residents of the island, who belong to Taiwan's aboriginal tribes, had quite a particular culture and history. On the other hand, the Han, who migrated from the Chinese mainland throughout history, each brought different traditions and customs. Essentially, this makes for a very vibrant and plural cultural landscape.

Its surrounding waters include, respectively, the East China Sea and the South China Sea to the west, while the Pacific Ocean is to the east. All of the waters are rich in marine resources, playing a very important role in Taiwan's economy and ecology.

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

Various main factors determine the coastal currents around Taiwan: First, there is the monsoon climate. In summer, the southwest monsoon brings warm and moist air, acting to stir up the direction and strength of the coastal currents, but in winter it is another story.

Yet another factor is underwater topography. Such complicated underwater relief with its trenches, ridges, and shallows may serve as a reason for changes in the flow of water. For instance, areas with deep trenches can have stronger currents, while shallow water areas will have slower flows.

Other factors include tides. The periodic rise and fall in the surrounding waters due to the tides may form tidal currents that interfere with shipping, fishing, and other marine activities.

Besides, the interaction with larger ocean currents from the Pacific Ocean and the South China Sea is able to affect coastal currents near Taiwan as well. These oceanic currents will bring about different water masses with different temperatures and salinities, further modifying the local current dynamics accordingly.

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

It is very important to take measurements of coastal currents in Taiwan for the understanding of the marine environment, safety of marine navigation, and management of marine resources. Traditional methods have employed buoys, drifters, and current meters for a long time. Above-mentioned methods have some limitations about accuracy and coverage.

In more recent times, coastal currents measurement has become more sophisticated with ease using Acoustic Doppler Current Profilers. The principle applied in ADCP doppler is based on the Doppler principle to measure the velocity of the flow of water.

3.1 How do ADCP using the Doppler principle work?

Acoustic Doppler Current Profiler(ADCP) emit a sonar signal into the water, which is reflected back by particles in the water, including suspended sediment and small life forms. The frequency of the returning sonar pulses shifts due to the Doppler effect created by the motion of the reflecting particles relative to the water flow velocity. This frequency shift can be interpreted by an ADCP to obtain an estimate of the current speed and direction at different depths.

The typical ADCP current meter consist of a transducer array that can be mounted in different ways onboard vessels, fixed structures, or even buoys. The transducer array broadcasts and receives the sound pulses in various directions in order to measure the three-dimensional currents.

3.2 What's needed for high-quality measurement of Taiwan coastal currents?

A number of considerations are indispensible in the measurement of coastal currents in Taiwan with precision. The equipment used has to be highly reliable. To this end, the ADCP current profiler should be made out of materials that ensure resistance against the salinity and corrosive nature of seawater.

Among all these materials, the titanium alloy is an ideal one for ADCP meter casings. The advantages are numerous. First, it is very resistant to corrosion, which is so necessary in this surrounding of salt water. It stands out when it comes to resisting dissolution due to sea water and marine organisms, hence ensuring a long life for the equipment. Secondly, the titanium alloy is hard but light. This makes it easy to handle and install, particularly on those mounting sites which are remote or unreachable.

Apart from material reliability, other factors include small size, low weight, low power consumption, and low cost. A compact and lightweight ADCP flow meter is easier to deploy and can be applied in a wider range of applications. Low power consumption allows for longer battery life or alternative power sources, such as solar panels. Low cost allows deploying a large number of ADCP profiler for the comprehensive coverage of the coastal area.

3.3 How to Choose the right equipment for current measurement?

While choosing the right equipment for measuring the currents in Taiwan, several factors have to be considered. The purpose for which the equipment is intended to be used is one of the cardinal considerations.

For measurements from a moving vessel, a ship-mounted ADCP will suffice. Real-time data of the current can be collected while the vessel is in motion through the water.

If the measurement needs to be conducted right on the seabed at a fixed location, then a bottom-mounted ADCP would be appropriate. Long-term measurements of the current can easily be recorded without any continuous maintenance.

If an application needs to be installed in open water or a fixed installation is not possible, a buoy-mounted ADCP is available. It is able to measure current over a large area and transmit wirelessly.

Selection of frequency-as far as water depths are concerned-different frequencies serve different water depths: for shallow waters of up to 70 meters, a 600 kHz ADCP would suffice, while for up to 110 meters, an ADCP at 300 kHz would be better. For deeper waters-acceptable to 1000 meters-the usage is typically a 75 kHz ADCP.

The well-known ADCP brands in the market currently are Teledyne RDI, Nortek, and Sontek. For customers who want value for their money but also quality, the best would be the China Sonar Panda ADCP. Since it is manufactured from an alloy of pure titanium, it is very durable and reliable. With state-of-the-art technology integrated into this model, it assures very good value for money. For further details and specifications on the China Sonar PandaADCP please refer to the following website: https://china-sonar.com.

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