How can we measure the coastal currents of Samtah?

1. Where is Samtah?

Samtah was a place with special geographical position. It was on the southern coast of Saudi Arabia. In the area of Samtah, there exists a beautiful coastal landscape characterized by sandy beaches with an arid mountain and plains backdrop.

The local culture in Samtah is very much affected by its vicinity to the sea. The fishing and maritime activities are part of the community's heritage that goes back ages. The waters that lie alongside the Arabian Sea are a great part of the area's identity. The Arabian Sea near Samtah is a dynamic body of water with an abundant marine life. It is home to many fish types, including species of utmost importance to the local fishing industry. The Samtah coastline contains several bays and inlets that provide sheltered areas for boats and are also very important in shaping the currents along the coast. The sea in this region experiences a range of weather conditions, from calm and sunny days to more turbulent times during the monsoon season.

2. What is the situation of the coastal currents near Samtah?

The coastal currents in the vicinity of Samtah have many influences. The tidal forces are a major constituent. The tides in the Arabian Sea are created by the gravitational pull of the moon and the sun. These tidal currents will vary in intensity and direction depending on the phase of the moon and other astronomical factors. Strong tides can indeed be responsible for significant changes in coastal current patterns.

Other decisive factors include the wind factor. Local predominant winds such as the monsoon winds are able to exert a very strong influence on the surface currents. The strong winds during monsoons cause water to travel in one direction and may even lead to the emergence of strong coastal currents at certain times. Seabed topography and shape of coastline play a deciding role. The underwater topography might also be deflecting or funneling the water, while the shape of bays and headlands can accelerate or decelerate the currents. Moreover, in gradients of water density that might be induced by factors such as temperature and salinity, differences in the movement of coastal currents may be caused.

3. How to observe the coastal water flow of Samtah?

There are a number of ways to observe the coastal water flow around Samtah. One of the ways is the surface drifting buoy method. Buoys are released into the water and are equipped with tracking devices such as GPS. As the buoys are carried by the surface currents, their movement can be monitored over time. By analyzing the position and speed of the buoys, the direction and velocity of the surface currents can be determined.

The other common method is the moored - ship method. A ship remains anchored in a location and current-measuring instruments are deployed from it. These instruments can measure speed and the direction of the water at different depths. However, this method has its drawback. The ship may influence the local current patterns and because it is kept stationary the area which can be measured is severely restricted.

The Acoustic Doppler Current Profiler (ADCP) method of measurement is more sophisticated and a lot easier to handle. They can also be installed on various carrier platforms such as boats and buoys, or deployed on the ocean floor. They measure a profile of the speed of the current from the water surface to a depth given by the instrument and should provide an even more holistic understanding of the current's structure.

4. How are the ADCPs applying the Doppler principle?

The operating principle of ADCPs is based on the Doppler principle. ADCPs transmit acoustic pulses into the water. Due to particles or objects moving in the current, some changes occur in the frequency of the reflected signal back from the target interrogated by the pulse. This frequency change, generally referred to as the Doppler shift, is proportional to the velocity of the moving target and, consequently, to the water current velocity.

The ADCP measures the Doppler shift of the reflected acoustic signals from multiple directions and at different depths. It calculates the speed and direction of the water current at each measurement point by analyzing these Doppler shifts. Usually, the device has a number of transducers that send and receive acoustic signals, thus enabling it to create a three-dimensional profile of the current.

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

Reliability of the materials should be used in the equipment for high-quality measurement of the coastal currents near Samtah. The casing of the measurement device should resist the corrosive action of the saltwater and the pressure exerted by the water at different levels. A small size and lightweight helps in easy installation and deployment on various platforms, either on buoys or small boats.

Especially for long-term measurement, the power consumption should be very low; cost-effectiveness is likewise relevant for large-scale measurement. One good option could be to use a titanium alloy for casing ADCPs. Because of its excellent corrosion resistance, the salty environment in the Arabian Sea is no problem for the use of a titanium alloy. It also can resist high pressure caused by a column of water.

6. How to Select appropriate equipment for current measurement?

The right equipment is selected based on its intended usage for the current measurement around Samtah. For ship-based measurements, the ADCP mounted on the ship shall be suitable to get the current information in real time when the ship moves across the waters. One bottom-mounted, or "sit-on-bottom," ADCP would also permit measurements near the seabed. This is necessary, because the currents measured at or close to the bottom are a crucial ingredient to understanding the interaction of the bottom and the water column. A buoy-mounted ADCP would be ideal to do both long-term and wide area measurements.

The choice of frequency also depends on the water depth. For water up to 70m in depth, a 600kHz ADCP is normally adequate. For depths to 110m, a 300kHz ADCP is typically better, and for deeper waters to 1000m, a 75kHz ADCP is typically more suitable.

There are well-known ADCP brands like 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.