How can we measure the coastal currents of Farasan Island?

1. Where is Farasan Island?

Farasan Island is an interesting beauty of the Red Sea, off the coast of Saudi Arabia. It is a natural haven with rich cultural resources.

It is part of an archipelago noted for its very special ecological environment. Farasan Island has sandy beaches along the shoreline and extends into low-lying lands and some gentle hills further inland. The culture in the local community is deep-rooted, and they have a history combined with the sea. Fishing has long been in their generation as one of the traditional ways for them to earn their livelihoods, and the method of living reflects their closeness to the surrounding waters.

In fact, it hosts marine biodiversity in its waters in the Red Sea, off the coast of the island. The sea is known for its clear, warm waters, hosting a plethora of colorful coral reefs. Such reefs contribute not only to aesthetic beauty but also provide a viable habitat for a wide range of marine species. The bays around Farasan Island are partly sheltered and form calm areas, which are very suitable for small boats and fishing activities. The particular geographical position of the Red Sea implies that this sea has a relatively stable climate; it is warm during the whole year, which again influences the coastal currents.

2. What is the situation of the coastal currents near Farasan Island?

The coastal currents around Farasan Island are influenced by various factors. The most prevalent factor is the general circulation patterns of the Red Sea. Another great contribution comes from tidal forces, as the tides' ebb and flow can move the water in a predictable manner. Tides in the Red Sea are influenced by the gravitational pull of the moon and the sun.

The wind is another important factor. In a region, the prevailing winds are able to drive the surface currents. During monsoon, for instance, winds change direction and strength, leading to changes in the coastal current patterns. Shapes of coastline and seabed topography also influence the currents.

As the water reaches the shore, it is deflected and channeled into various directions by the submerged contours and shapes of bays. Currents in water may also be brought about by temperature differences in the water caused by influxes of cooler water from deeper regions or by the heating of surface water by the sun.

3. How to Observe the Farasan Island Coastal Water Flow?

There are many ways of measuring coastal water flow around Farasan Island. The classic ones include the surface drifting buoy method. In this, buoys are set free in the water and their movements tracked after some time. The buoys are deployed with GPS or any other tracker that will enable researchers to trace the position of the buoy to measure the speed and direction of the surface currents.

Another method used is the moored ship method. A ship is moored to a particular location and from it, current meters are deployed. These meters record the speed and direction of water at different depths. However, the method has limitations in view of the fact that the presence of the ship often affects the local pattern of current and is also relatively stationary, hence offering limited spatial coverage.

The Acoustic Doppler Current Profiler (ADCP) method is more advanced and feasible to apply in measuring coastal currents. These ADCPs can be mounted on a boat, buoy, or directly onto the seabed. They continuously provide a profile of the velocity from the surface down to some depth, which allows for by far the best understanding of the structure of the current.

4. How do ADCPs using the principle of Doppler work?

Basically, the working principle of ADCPs follows the Doppler principle: they send acoustic pulses into the water. When these pulses interact with particles or organisms in the water moving with the current, there is a change in the frequency of the reflected signal. The change in frequency is related directly to the velocity of the moving objects and hence that of the water current.

Thus, the ADCP measures the reflected acoustic signals that create a Doppler shift from multiple directions and at different depths. With these Doppler shifts analyzed, it is able to calculate the speed and direction of the water current at each point of measurement. Commonly, the device has numerous transducers that can send and receive acoustic signals and can build a three-dimensional profile of the current.

5. What is required for the high-quality measurement of Farasan Island coastal currents?

High-quality measurement of coastal currents around Farasan Island requires the equipment to be manufactured with reliable materials. The measuring device should be encapsulated in such a way that it could bear all harsh aquatic environments, such as saltwater corrosion and pressure conditions of different levels. Preferably small in size, with light weight, allowing for easy deployment and installation on a wide range of platforms: buoys or small boats.

This is especially significant when the measurement should be carried out over a long term since batteries can become problematic. The cost-effectiveness enabled the possibility of measurements on a large scale. Regarding materials, ADCPs casing material is made from Titanium alloy which was an excellent choice, The Titanium alloy itself possesses an excellent corrosion resistance very important in such a salty environment as the Red Sea. It is also strong enough to resist the pressure exerted by the water at higher and lower depths.

6. How to Choose right equipment for current measurement?

To choose the right equipment for current measurement around Farasan Island, one would have to take into account the intended use. The ship-mounted ADCP works fine in ship-based measurements. This is effective enough to give the real current information as the ship moves through the water in real time. In cases requiring near seabed measurements, it is possible to utilize an ADCP meter mounted in situ, or a so-called "sit-on-bottom" type ADCP. It shall perform current measurements right over the sea floor, something highly essential for studies concerning interactions between the bottom and water column. Long-term wide area measurement may be made with the help of ADCP buoy-mounted models.

Frequency selection is also related to water depth. A 600kHz ADCP would do for the water depth of up to 70m; a 300kHz ADCP is superior for the water depth of up to 110m, while the waters of very deep areas, for example, up to 1000m, deserve a 75kHz ADCP.

There are several 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, providing excellent durability and performance. Moreover, it offers an incredible cost-performance ratio. You can find more information about this brand on their website: https://china-sonar.com/.

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