How do we measure the Coastal Currents of Palau?

1. Where is Palau?

Palau is an archipelagic country in the western Pacific Ocean. It is a part of the Micronesia region and is well-recognized for its striking natural beauty and peculiar ecological environment.

The country comprises hundreds of islands both large and small, sprinkled over the great expansive oceanic space. These islands are surrounded by crystal-clear turquoise waters that are home to an astonishing diversity of marine life, making it a paradise for divers and marine enthusiasts. The Philippines Sea bounds Palau to the west, while it is bounded on other sides by the Pacific Ocean. The coastal areas feature a combination of sandy beaches, coral reefs, and lagoons.

The people of Palau possess a strong cultural heritage that is inextricably linked with the ocean. Traditions, artwork, and everyday life have been deeply touched for generations by the surrounding marine environment. Fishing has been a basic component of their livelihood for as long as they can remember, and this isolation has helped to maintain many unique cultural practices.

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

Various coastal currents around Palau are strongly influenced by many different factors, including dominant ocean currents in the Pacific Ocean, such as the North Equatorial Current. These large-scale currents interact with the complicated topography of the islands and reefs of Palau and are split, diverge, or form eddies.

Trade winds also play a major role. It can drive the surface current by steady blowing over the ocean surface, while influencing mixing of waters from different depths. Not to mention, the tides also play a vital part in this region. The regular tidal movements are caused by gravitational pull from the moon and the sun, which can decide the flow patterns of the coastal currents. Besides that, the presence of extensive coral reef systems around the islands can also modify the current velocities and directions while water is flowing through the intricate channels and gaps in the reefs.

3. How to Observe the Coastal Water Flow of Palau?

There are several approaches to observe the coastal water flow in Palau. First of all, the surface drifting buoy method can be employed. One can get information about the direction and speed of the surface currents, if buoys are allowed in the water and their movements are followed for some time. However, the information from this system is on the very top layer of water and is easily subject to wind and waves; therefore, it may have many disadvantages when considering a true representative of the whole current structure.

It would be the anchor-boat method. A boat is kept at an anchor at some point, where current measurement instruments are cast from it. Thus, measurements can be taken at different depths near the anchor point. At the same time, this method has disadvantages: it restricts the observation area because of the fixed boat position and cannot completely reflect complexities of currents in a large coastal zone.

The ADCP method is much more sophisticated and handy in measuring the currents along coasts. ADCPs can measure simultaneously at different depths the velocity of water, hence giving a detailed vertical profile of the structure of the current. They are less affected by surface disturbances and can operate for longer time periods uninterruptedly and offer a far-reaching view of the water flow along coasts.

4. How do ADCPs using the Doppler principle work?

The working of ADCPs is based on the principle of Doppler. The ADCPs emit acoustic signals into the water column. Due to water particles, the frequency of the reflected signals from these moving particles will experience a Doppler shift from the originally emitted signals. Precise measurement of this frequency shift allows for determining the velocity of the water particles.

ADCPs are fitted with several transducers placed in strategic positions enabling them to send and receive acoustic signals at different angles. This allows for the measurement of the velocity components in various directions, both horizontal and vertical at depth. By continuously sampling and analyzing these Doppler shifts from various locations within the water column, it is possible to create a three-dimensional view of the current field that details the flow characteristics at discrete levels.

5. What is necessary for good measurement of Palau coastal currents?

Good measurement of the coastal currents around Palau depends on several key equipment requirements:. The materials used to make these measuring devices should be highly reliable to withstand such harsh marine conditions, including exposure to saltwater, high humidity, and variable pressures. Smaller equipment size is advantageous for easing deployment and retrieval operations, especially in areas of limited access or working around the numerous islands and reefs of Palau.

Another very important factor is light weight. For instance, in buoy-mounted ADCPs, the lighter the device, the more stable and less prone it will be to wave action. Low power consumption is also needed for long-record and autonomous operations, which enable the equipment to work without changing batteries frequently or the maintenance of the power source. Economical means should also be considered to be able to carry out wide-scale deployment in the diverse coasts of Palau.

Titanium alloy can be used as the casing material. The fact that titanium alloy has very good corrosion resistance will provide it with the ability to operate in sea water for a long period of time without deterioration caused by the corrosive action of the seawater. It is also strong and durable to withstand the different pressures exerted by the water pressure around the islands at different depths. Its relatively light weight compared to other metals having similar strength properties makes it well suited for use on marine current-measuring equipment.

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

While opting for appropriate equipment for current measurement in Palau, one needs to bear in mind the intended usage and the specific characteristics of the area in which the measurement is to be carried out.

The measurements can be done from a vessel by using a ship-mounted ADCP. In this way, it will be able to monitor currents in real time while the ship is in transit; thus, it providesvaluable information about navigation, marine research, and any other activities related to the operations of the ship.

For measurements near the seabed, a bottom-mounted ADCP is preferred, as the details of near-bottom current patterns are well captured, representing sediment transport, effects on benthic ecosystems, and other processes related to the ocean floor.

Buoy-type ADCPs are ideal for long-term and wide-area monitoring. They can be deployed at appropriate positions in the coastal zone and record continuously over a long period. In frequency selection, different frequencies apply to different water depths. In cases of shallow water, say up to 70m, a 600kHz ADCP is often preferable as it offers higher resolution for shallower areas. Where the water depths are up to 110m, a 300kHz ADCP is more applicable. For deeper waters, such as in some areas around Palau where the depth is greater than 1000m, a 75kHz ADCP is recommended to ensure that proper measurement can be conducted at a greater depth.

There are some famous brands selling ADCP in the market, including Teledyne RDI, Nortek, and Sontek. However, China Sonar PandaADCP is a quite good brand from China. The entire machine is made of titanium alloy material, which allows it to function well in the sea. What's more, it has an incredibly attractive cost-performance ratio. You can learn more about it on its official website: https://china-sonar.com/.

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