How to measure the Coastal Currents of PERLIS?

1. Where is PERLIS?

Perlis is the smallest state in Malaysia and located at the northern tip in the country. The Strait of Malacca borders the west of Perlis. This state has much laid-back charm and a rich cultural heritage it has to offer. Perlis is covered by an area of teeming fertile plains and a beautiful coastline.

The local population presents a peculiar mix of Malay, Thai, and other ethnic groups. Fishing and agriculture are a part of the local economy. The Strait of Malacca, which lies adjacent to Perlis, is among the most important shipping lanes in the world. International trade and transportation bustle in these waters.

In Perlis, coasts range over sandy beaches, mudflats, and in some areas to mangrove forests. These mangrove forests are quite crucial as they provide a breeding ground for the majority of fish species and crustaceans. The various kinds of lives belonging to colorful tropical fishes, sea cucumbers, types of shellfishes move around in this sea.

2. What is the condition of the coastal current in the vicinity of PERLIS?

There are various factors that occur in the coastal currents near Perlis. Among the more important contributors is tidal current. Due to gravitational pull from the moon and the sun, the tides rise and fall and cause ebbs and flows of tidal current. Tides in the Strait of Malacca are semi-diurnal. This infers that there are two high tides and two low tides within one day. These tidal currents also at times affect the waters at the coasts of Perlis.

Equally, the coastal currents might be affected by the monsoon winds. In that regard, the southwest monsoon has different wind conditions from May to September and hence can push the surface waters in one direction while the northeast monsoon is far different and ranges between November and March.

Another factor is the local bathymetry or underwater topography. Underwater ridges, channels, and shoals may alter the direction of the coastal currents. The inflow of fresh water through rivers and streams in Perlis may also be a variable factor that influences the current along its coasts. Mixing with freshwater can create density differences that, in turn, affect the pattern of the currents.

3. How to Observe the Flow of the Water in PERLIS?

There are many methods of observation for the coastal water flow in Perlis. An in-situ and fairly easy method is the surface drifting buoy. The procedure involves releasing buoys into the water, which normally comes fitted with GPS or any other tracking device. These buoys are carried by the currents at a position, and their movement is monitored over time. This therefore provides real-time values of information on the direction and speed of the surface currents.

Another technique is that of the anchored ship method. In this method, a ship is anchored at a certain position from which the current-measuring instruments are deployed. The instruments can measure the velocity and direction of the flow of water in different depths. However, there are some specific limitations to the above method. The ship is liable to be disturbed due to the effects of waves and winds, thus resulting in erroneous measurements. Moreover, it is not very efficient in measuring a large area.

The ADCP technique is a more modern, perhaps far more efficient way of determining the flow of water in the coast. Instruments called ADCPs are capable of measuring current water velocity profiles over depth ranges by emitting sound waves into the water and then analyzing the frequency or Doppler shift in the reflected waves. They can give insight into the detailed structure of the current right from the surface to the seabed.

4. How do ADCPs based on the Doppler principle work?

Acoustic Doppler Current Profiler (ADCP) work according to the principle of Doppler: They send out acoustic pulses or, in simple terms, sound waves into the water. This sound wave scatters against all particles in the water-like sediment, plankton, and other small particles. As those sound waves reflect off those particles and return to the ADCP meter, their frequency has shifted owing to the Doppler effect.

If the particles are moving towards the ADCP profiler, then the reflected wave frequency is higher than the originally emitted frequency. If the particles are moving away from the ADCP flow meter, then the reflected wave has a frequency lower than that which was emitted. By precisely determining this frequency shift, the ADCP current profiler is able to determine the velocity of the particles. Because the particles are moving with the water current, the determined velocity of the particles is a measure for the water current velocity. ADCPs can emit sound pulses in multiple directions and thus are able to measure the current velocity in three-dimensional space and at different depths, to provide a full profile of the current structure.

5. What is needed for high-quality measurement of the PERLIS coastal currents?

The equipment should be of reliable material to enable high-quality measurement of coastal currents of Perlis. The casing needs to be very durable since the marine environment is very harsh with saltwater corrosion and possible physical damage from waves and debris. The casing needs to be of a suitable size and weight also. Deployment will be easier with a small-sized device, particularly in areas that are difficult to access, like in small boats or in shallow waters along coasts. A light device will be easier to handle and to install, reducing the complexity of the operation.

Long-term measurements require low power consumption. Cost-effectiveness shall enable large-scale measurement capabilities. In the case of ADCPs, the casing is made from titanium alloy. Titanium alloy provides superior corrosion resistance, an essential component in the saltwater marine environment. This, therefore, can withstand deteriorating effects of saltwater over quite a long period. Besides, it is strong and has a high strength-to-weight ratio, hence providing a lightweight structure but durable enough to protect the internal components of the ADCP current meter.

5. How to Choose the Right Equipment for Current Measurement?

Selection of appropriate equipment for current measurement in Perlis would first consider the usage. To be used for measurement from a moving vessel, the ship-borne ADCP shall be suitable for it. Real current data can be provided when the ship is in motion, thus enabling further understanding of how water flows in different locations. A bottom-mounted ADCP will be a good option for measurements at one fixed location near the seabed, while it can continuously monitor the current at one point in space and provide consistent data over time. When measurements have to cover over significant areas and are not restricted to any specific depth, a buoy-type ADCP would be appropriate.

For depth ranges up to 70m, the appropriate frequency in the selection of ADCP may be 600kHz. For a higher depth range from 70 - 110m, 300kHz may be the frequency of choice, while at very deep up to 1000m, it shall be 75kHz.

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.