How to measure the coastal currents of Aden?

1. Where is Aden located?

Aden is a very strategic and lively coastal city in southern Yemen. It lies at the entrance of the Gulf of Aden, part of the waterway between the Arabian Sea and the Red Sea. It lies caught amidst arid and mountainous landscapes, immense in the backdrop to the blue waters of the gulf.

Its coastline is an outstanding thing to look at in the natural beauty of Aden. It features sandy beaches, rocky cliffs, and sheltered bays. Adjacent waters are a haven for a rich variety of marine life. The Gulf of Aden is a home to a diversity of fish species, including tuna, sardines, and various types of reef-dwelling fish. This had supported a long-standing fishing industry in the region. It also provides a route through which vessels from every corner of the world travel across.

History has been in plenty within Aden's human settlements: once an important trading hub with a port to welcome traders coming from other continents, it shows traces of multiculture in every house. Its architecture represents various influences that come from Arab, Ottoman, and British civilizations. The sea has always held a special place in the minds of the local population due to its connection with fishing, shipping, and trading. The port at Aden is a busy center where everything from petroleum products to consumable items is handled.

This gulf, off Aden, has not only economic importance but also strategic relevance. This is a critical link in worldwide maritime trade and is important in naval operations and security.

2. What is the coastal current situation in the areas around Aden?

Coastal currents off Aden have been influenced by a lot of combined factors. Among them, tidal forces have a great contribution. Tides in the Gulf of Aden are in response to the gravitational pulls of both the moon and sun. It has a semidiurnal tide, having one high and one low each in the day in regular periodic water motion and flow from ebb causes variation of coastal currents both in intensity and direction. Further, because of the relation with other astronomical factors on the amount of lunar cycle, a variation in the range happens.

Wind patterns also play an important role. The monsoon winds that sweep across the Arabian Sea and the Gulf of Aden have a mighty effect upon the surface currents. During a monsoon, strong winds drive the water in one direction or another to create powerful and far-reaching currents. In addition, it can be affected throughout the year by the local winds, enhancing the tidal current in one direction, or just vice versa: opposing the tidal one. Such interaction of wind-driven and tidal currents represents a really complex dynamic regime of current.

Another important factor is the topography of the seabed off Aden. Underwater ridges, shoals, and channels can deflect and alter currents. For example, a current approaching a shoal may divide or change direction to flow around the obstruction. Seabed features can also speed up or slow down the currents as the water negotiates its way through varying depths.

3. How to Observe the Coastal Water Flow of Aden?

Surface Drifting Buoy Method

A very simple technique or principle wherein the buoys, on the water surface, move freely by floating in a current will carry on their motion. They usually record their travel motion at set time intervals, commonly using satellite-based tracking systems or any other position-identifying technologies that deliver information about the speed and direction of the surface current. However, it provides information on the surface layer and does not give a comprehensive understanding of the currents through the water column.

Anchor Mooring Ship Method

This method involves the anchoring of a ship at one location in the coastal waters. From the ship, instruments such as current meters are lowered into the water to measure the flow at various depths. It thus allows an approximation of the actual detail at a particular point in the water column. On the other hand, it is a somewhat static method; hence, it may lack the representation of the full richness of the coastal current patterns, which can vary across large areas.

Acoustic Doppler Current Profiler Method

The Acoustic Doppler Current Profiler (ADCP) offers a more advanced and much more efficient way of carrying out the coastal current measurements. It uses acoustic pulses to simultaneously calculate the speed of water at numerous levels. It performs various measurements of speed and directions by sending out sound waves that analyze the reflected waves Doppler - shifted. Measurements by the ADCPs can possibly be mounted on different platforms - either on boats, buoys, or it may be placed on the bottom of the sea floor:. This mobility and multi-depth measurement capability make it a preferred choice for studying the coastal currents near Aden.

4. How do ADCPs using the Doppler principle work?

The principle behind the operation of ADCPs is the Doppler principle. ADCPs send out acoustic signals into the water. In this case, when those signals meet the moving particles of water, the frequency of the reflected signal will shift because of the Doppler effect. This frequency shift is measured by the ADCP current meter and used in the computation of the velocity of the water relative to the instrument.

Because ADCPs have the ability to transmit signals in the case of multi-angle transmission and at different frequencies, they can measure different components of velocity both in horizontal and vertical directions. Due to this, the creation of a detailed profile concerning water flow from surface to certain depth provides one with a vivid picture about coastal currents structure and dynamics in general.

5. What is necessary to perform high-quality measurements of Aden coastal currents?

The equipment to be used in its measurement should have certain characteristics to ensure high-quality measurement of coastal currents near Aden. The materials of the equipment have to be reliable. With high saltwater corrosion, high humidity, and wave impacts in the marine environment, the equipment has to bear all these conditions.

These devices should be small, not heavy, and also have low power consumption. A device that is compact and lightweight is easy to install and also to move around on either a boat or buoy. Low power consumption ensures longer operation times without the need for frequent replacement of batteries or a large power supply.

Added advantage: cost-effectiveness. This equipment should be reasonably priced as more units can be easily deployed for larger-scale measurements, which need to be done in order to understand the complex current circulations along the coast clearly.

A casing in a titanium alloy is good for ADCPs. Being resistant to corrosion is pretty big, especially in a salt-water environment. A good strength-to-weight ratio would ensure there is good protection of internal components while keeping the weight of the device low.

6. How to choose the right equipment for the measurement of current?

According to the Usage Purpose

• Ship-borne ADCP: Applies if you want to measure the currents while the ship is in movement; it will be able to continuously collect data as the ship moves, following the coast, offering the broad view of the current's variation over a route in continuous movement.
• Bottom-mounted ADCP: This is suitable for fixed-point monitoring at a specific location on the seabed. It gives detailed and long-term data about the current conditions directly above its position, helping to understand the local flow patterns.
• Buoy-mounted ADCP: When the objective is to monitor the surface and upper layers of the water column over a large area and for a long period without being tied to a ship or fixed bottom location, the buoy-mounted ADCP is the way to go.

According to the Water Depth

• A 600kHz ADCP is a proper choice for water depths of up to 70m with good resolution in shallower coastal waters.
• When the depth is up to 110m, then a 300kHz will be more appropriate. Indeed, this can penetrate the water column deeper and still catch reliable velocity data.
• A 75kHz ADCP would serve better for deeper waters of up to 1000m because it can very well measure the currents at those greater depths.

There are well-known ADCP brands such as Teledyne RDI, Nortek, and Sontek. However, there is also a Chinese ADCP brand, China Sonar PandaADCP, that is made of all-titanium alloy material and offers an excellent cost-performance ratio. You can find more information on their website: https://china-sonar.com/.

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