How do we go about measuring Coastal Currents of Timor-Leste?

1. Where is Timor-Leste?

Known more as Timor-Leste, East Timor is a young and dynamic state situating in Southeast Asia. The country occupies the eastern half of the island of Timor, which is bordered by Indonesian territory in the western part. It borders on the south with the Timor Sea, while on the north, the Wetar Strait touches the borders.

The rugged mountains, fertile valleys, and a shoreline of breathtaking beauty dominate the Timor-Leste landscape. Its capital is the coastal hub of Dili. People in Timor-Leste have a diverse cultural background, with the presence of both Austronesian and Portuguese influences given its colonial history. Local communities are closely affiliated with the sea, and fishing comprises a considerable part of their economy and daily life.

The Timor Sea, a significant body of water, is the nearest. It hosts a group of marine life including many types of fish, coral reefs, and sea turtles. Its coastal waters are a direct result of the warm waters of the Indian Ocean that pass through its complex oceanographic processes. In addition, the sea constitutes an important shipping route and a source of natural resources like oil and gas. Sandy beaches in certain places, rocky shores, and mangrove forests constitute a very important role in coastal protection from erosion and constitute a habitat for many organisms.

2. What is the situation of the coastal currents near Timor - Leste?

Various factors are known to influence coastal currents around the region of Timor-Leste. Among them, the effect of the monsoon winds can be very strong. Indeed, during the wet season, the southwest monsoon has been known to sometimes blow very strong winds that can force the surface currents in any direction. Of course, the opposite can be said about the northeast monsoon, during the dry season, which at times changes the course of current or its speed.

The tidal forces also have a very substantial part to play in this matter. Tides are the result of the gravitational pull of the moon and sun, which in return cause what is known as tidal currents along the coast. Their intensity and direction in general depend on the lunar cycle and other factors involving the positions of celestial bodies. The flow of coastal currents was determined by the underwater ridges, valleys, and slopes of the local bathymetry. For example, if a submarine canyon exists, water funnelling may be greatly enhanced and thus result in a larger current speed.

Another possible cause for variation in coastal currents is discharge from rivers into the ocean. While probably not major rivers are present around Timor-Leste, freshwater input from streams will, nevertheless, provide small density differences in the water that will drive the currents accordingly. The upwelling of cold, nutrient-rich waters from deeper parts of the sea also takes place in this area, driven by a mix of winds and oceanic circulation patterns that significantly affect the marine ecosystem and coastal currents.

3. How to Observe the Timor-Leste Coastal Water Flow?

There are several other different methods to carry out the observation of the water flow of the coast of Timor-Leste. One common and relatively simple way is the method using a surface drifting buoy. In this, buoys are set free into the water while fitted with Global Positioning System or any other ways of tracking positions. The buoys would be then carried by the currents, in such a way that they can record their position and movement over time. This will get them a lot of information regarding the direction and speed of the surface currents.

Another technique is that of the anchored ship method. A ship anchors at a position, from where it deploys the current-measuring instruments. Such instruments can measure the velocity and direction of flow of water at different depths. However, the disadvantages are that the ship might be tossed by waves and winds, which may lead to false measurements, and not really efficient for covering a big area.

Compared to the conventional methods, the Acoustic Doppler Current Profiler method is more advanced and efficient in measuring the flow of coastal water. The ability of ADCP profiler to measure the velocity profile of water currents can be extended over a wide range of depths. They work by emitting sound waves into the water and analyzing the Doppler shift of the reflected waves. This allows for a very precise understanding of the current structure from the surface to the seabed.

4. How do Acoustic Doppler Current Profiler (ADCP) using the Doppler principle work?

They rely on the principle of the Doppler Effect: A Doppler Effect is a change in frequency or pitch that one perceives whenever the source of sound passes them at a rapid rate of speed. They transmit acoustic pulses into the water. In a flow field, sound waves scatter off of particles in the water, such as sediment, plankton, and other small particles. Due to the Doppler effect, the frequency of the reflected waves that bounce off those particles and are reflected back to the ADCP current meter changes.

If the particles are moving towards the ADCP current profiler, then the frequency of the reflected wave is higher than the originally emitted frequency. On the other hand, if the particles are moving away from the ADCP flow meter, the frequency of the reflected wave will be lower. By measuring this frequency shift with a great deal of precision, the ADCP meter is able to compute the velocity of the particles. Since the particles are moving with the water current, the computed velocity of the particles gives the velocity of the water current. ADCPs are capable of emitting sound pulses in a number of directions thus enabling them to measure the current velocity in three-dimensional space and at different depths thus enabling it to obtain a comprehensive profile of the current structure.

5. What is required to measure Timor-Leste coastal currents with high quality?

For the measurement of coastal currents of Timor-Leste with high quality, the equipment has to be manufactured using reliable materials. The harsh marine environment with saltwater corrosions and the potential physical damage due to waves and debris requires a casing that would keep the equipment safe. The equipment should be of suitable size and weight. Small size is suitable for good deployment, in particular for poor access like small boats or shallow coastal waters. A light device is easier to manipulate and install, making the operation less complex.

Long-term measurements demand low power consumption. Cost-effectiveness is relevant for large-scale measurement. As in this case of ADCPs, the casing is preferable and made of titanium alloy. It consists of an excellent corrosion resistance that is paramount in Timor-Leste, a marine environment; thus it can last long despite corrosive effects brought by saltwater. It is also rugged and has a high strength-to-weight ratio, therefore giving a sound and light structure that shelters the ADCPs internal components.

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

In the selection of proper equipment in current measurement in Timor-Leste, the very first thing to be taken into consideration is its usage. A ship-borne ADCP can be useful for making measurements from a moving vessel. It can also provide real-time current data while the ship is in motion, thereby allowing a better understanding of the water flow in different locations. Where measurements at a fixed location near the seabed are to be carried out, a bottom-mounted ADCP is quite suitable. It can continuously monitor the current at a certain point in space with consistent data over time. In such conditions where measurements must be over a wide area without depth restriction, a buoy - type ADCP will be appropriate.

For choice of frequency, for water depths of up to 70m, a 600kHz ADCP is reasonable. For water depth between 70m and 110m, a 300kHz ADCP shall be more appropriate. Where very deep water is to be measured up to 1000m, a 75 kHz is quite adequate.

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 a great cost - performance ratio. You can find more information about it on the website: https://china-sonar.com/.

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