How to measure Indonesia's coastal currents?

1. What is the situation of coastal currents around Indonesia?

Indonesia is an archipelagic country, having a coastline extending in almost all oceans and seas. The situation of the coastal currents near Indonesia is very complicated because of a combination of reasons. This country falls within the equatorial region of earth, where the climatic and oceanographic conditions remain entirely different compared to any other geographical entity.

The warm, natural waters of the Pacific Ocean and the Indian Ocean interact around Indonesia, creating a dynamic system of currents. Monsoon winds also play an important role in the way the coastal currents are formed. The winds blow from the northeast during the northeast monsoon and from the southwest during the southwest monsoon. These winds can cause changes in direction and strength of the currents.

The complex bathymetry of Indonesian seas and oceans introduces more complexity into the coastal currents. Further splits, combinations, or even changes in directions of these currents are the result of the presence of islands, reefs, and shallow areas. Besides that, tides and larger-scale oceanic circulation also affect coastal currents.

2. What are the factors that influence the coastal water flow of Indonesia?

A number of factors have a cardinal effect on the flow of water on Indonesia's coasts:

Monsoon Winds: As highlighted earlier, the monsoon winds are among the key drivers of surface current movements. The shift in wind direction and velocity from one season to another tends to provide wide variations in currents along the coasts.

Oceanic Circulation: The large-scale oceanic circulation features, including the Indonesian Throughflow and the Equatorial Currents, carry various water masses of dissimilar temperatures and salinity. These interact with the coastal waters of Indonesia and affect local current systems.

The Tides: This is the periodic rise and fall of water level motion, a result of tidal friction, which in turn causes the tide current. The range and timing of tides vary along the coasts.

Bathymetry: The complicated bathymetry, in terms of multiple islands, reefs, and shallowness within Indonesia's seas and oceans, has a strong influence on the currents that occur along its coasts. These may be influenced by things such as narrow channels, shallow banks, and deep canyons.

River Discharge: Several great rivers that run into the ocean may, simultaneously, be another cause for variations in coastal currents. Along with freshwater discharge, salinity and temperature variations in the water will more than likely create local currents' patterns.

3. How to Observe the Indonesian Coastal Water Flow?

The measurement of Indonesia's coastal water flow is very important in providing insight into the marine environment, natural disaster forecasting - especially with regard to tsunamis and storm surges - and in coastal management. Coastal current observation can be done by several methods, though recently, the ADCP is a widely used instrument because of its precision and ease of operation.

3.1 How do Acoustic Doppler Current Profiler(ADCP) using the principle of Doppler work?

The principle behind ADCP is the emission of sound waves through water and the measurement of the frequency shift of the reflected waves. The frequency shift is due to the movement of the water particles, which is related to the velocity of the current. By analyzing the frequency shift at different depths, the ADCP are able to determine the velocity of the water current at each depth.

ADCP current meter normally consist of a projection of a transducer array that emits and receives sound waves. The transducer array is usually mounted on a ship, buoy, or another platform. A moving platform through the water enables the ADCP current profiler to measure the water velocity relative to the moving platform. By subtracting the velocity of the platform from the measured water velocity, the true velocity of the current can be determined.

3.2 What is required for quality measurement of Indonesia coastal currents? The following features are necessary to provide high-quality measurement of Indonesian coastal currents:

Reliability: The measurement equipment should be reliable in harsh marine conditions, such as resistant to corrosion, shock, and vibration.

Small Size and Light Weight: The small-size and lightweight equipment is easy to deploy and operate at remote or hard-to-reach areas.

Low Power Consumption: Low power consumption is of prime importance for long-term deployment as well as for minimising the cost and environmental impact of the measurement system.

Low Cost: Cost is always one of the constraints, especially for large-scale measurement campaigns. This is because inexpensive equipment allows the collection and analysis of more extensive data.

The ADCP doppler shell is best made of titanium alloy material. Titanium alloy enjoys many advantages: high strength, corrosion resistance, light weight, which makes it very suitable for ocean use because it would withstand the harsh conditions of the ocean and offer long-term protection to the sensitive electronics inside the ADCP flow meter.

3.3 How to Choose the right equipment for current measurement?

When one has to select the proper equipment to conduct the measurement of currents along coasts in Indonesia, several items must be considered, such as the following:

Intended Use: Define the application for which the measurement is required. For example, if the measurement has to be made from a ship, the best would be an ADCP meter installed on the ship. If the measurement is required over a long duration at a fixed location, an ADCP profiler fixed on the bottom or mounted on a buoy will be more appropriate.

Frequency Selection: Different frequencies suit different water depths. For shallow waters around the coast, a higher frequency ADCP, such as 600 kHz, would be good up to 70 meters in depth. To go even deeper in the waters, it may require a lower frequency of 300 kHz or 75 kHz ADCP.

Finally, as for ADCP manufacturers, there are not a few famous brands in the market. Some well-known brands include Teledyne RDI, Nortek, Sontek, and China Sonar etc..  Of them, from China Sonar PandaADCP is incomparable in quality, with all-titanium alloy construction while offering great value for money. The website for China Sonar is https://china-sonar.com.

Here is a list of some popular ADCP brands and models: