How to measure the coastal currents of Pilipinas?

1. What is the situation of the coastal currents near Pilipinas?

The coastal currents near Pilipinas are influenced by a large variety of factors. The Philippines is an archipelagic country in Southeast Asia surrounded by the Pacific Ocean and the South China Sea. With such complex geography and oceanographic conditions, the current patterns ought to be diverse.

Along the Philippine coastlines are dynamic current systems formed by the interaction of the western Pacific Ocean waters and the cooler waters from the South China Sea. These are thus influenced by such other factors as wind patterns, tides, bathymetry, and larger-scale oceanic circulation.

2. What are the factors influencing the coastal water flow of Pilipinas?

Among the important factors affecting the coastal water flow of Pilipinas are:

Wind Patterns: Surface winds blowing over the ocean surface can generate surface currents. Much in the Philippines depends on monsoon winds, the northeast monsoon bringing in cooler and drier air from November to February, and the southwest monsoon bringing in warmer and more humid air from June to September. These could bring in the shifting of the direction and strength of coastal currents.

Tides is the other important contributory factor. Tidal forces are created by the rise and fall of tides, which, in turn, acts in a channeling way upon the movement of water along any coast. In some parts of the world, tidal ranges are great, thus causing strong tidal currents.

Bathymetry: The shape and depth of the ocean floor are equally drivers of coastal currents. Where narrow channels, shallow areas, and submarine ridges lie, current velocity can increase and alter direction. In the case of the Philippines, with more than 7,000 islands, the complex bathymetry has given it different patterns in its current.

Oceanic Circulation: It is also influenced by the larger-scale oceanic circulation patterns such as the Kuroshio Current and the Mindanao Current. These currents carry warm or cool waters to the region and thus determine the temperature and salinity conditions of the coastal waters.

3. How to observe Pilipinas Coastal Water Flow?

Velocity and volume are the two major parameters of coastal currents that play an important role in many applications with respect to Pilipinas, for example, in marine navigation, fisheries management, and environmental studies. Conventionally, measurement of coastal currents was performed through various techniques like drift bottles, current meters, and shipboard observations. The alternative techniques have, however had considerable shortfalls with respect to accuracy, spatial coverage, and temporal resolution.

More recently, a superior and much more convenient way of making such measurements of coastal currents has emerged in the form of the range of ADCP. The method makes use of the Doppler principle to measure the velocity of water currents simultaneously at several depths.

3.1 How do Doppler Principle ADCP work?

Acoustic Doppler Current Profiler (ADCP) generate sound waves into the water and measure the frequency shift of the returned sound waves. The frequency shift can be considered as occurring due to the movement of the water particles, related to the velocity of the current. The frequency shift in every depth, as determined by the ADCP, reflects the velocity of the water current.

In general, an ADCP current meter typically has a transducer array that sends out and receives sound waves. The transducer array would be mounted on a ship or buoy or some other platform. A moving platform through the water will then measure the velocity of the water relative to the ADCP through a Doppler shift via the ADCP. By subtracting the platform's velocity from the measured water velocity, true velocity of the water current can be determined.

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

Several factors will be engaged in high-quality measurement of Pilipinas coastal currents. The primary consideration is the reliability consideration of the measurement equipment. The equipment should be sound enough to be used in a harsh marine environment and provide accurate and consistent measurements over a long period of time.

The key factors besides reliability are small size, lightweight, low power consumption, and low cost. All of these ensure the successful deployment and operation of the equipment, as well as the large volume of measurements that can be performed.

The shell of ADCP current profiler is preferably made by the material of titanium alloy. Titanium alloy contains so many advantages, which includes high strength, corrosion resistance, and light weight. All these characteristics make it an ideal material for marine purposes. This alloy can withstand the corrosive effects of salt water and provide long-term protection to the ADCP doppler.

3.3 How to choose the right equipment for current measurement?

Several factors are very vital in choosing appropriate equipment for measurement of the coastal currents in Pilipinas: the intended application of the equipment. All applications cannot use one type of ADCP flow meter. For example, the shipboard ADCP will be appropriate for measurements when the ship is in motion, while bottom-mounted ADCP  can be used to measure at one location for a longer duration. Buoy-mounted ADCP will provide real current conditions in the specific area.

Another important determinant is the ADCP profiler frequency, which is different for different water depths. For example, a 600 kHz ADCP shall be suitable for water of up to 70 meters deep, 300 kHz for as high as 110 meters, and 75 kHz for as high as 1000 meters.

Finally, brand and reputation count in choosing the ADCP instrument. For the ADCP market, there are some popular brands: Teledyne RDI, Nortek, Sontek, and China Sonar. Among them, PandaADCP from China Sonar provides high quality all-titanium alloy construction and unbeatable value. The website for China Sonar is https://china-sonar.com.

Below is given a list of some of the popular brands and their models for ADCP.