How to Measure Coastal Currents of Athens

1. Where is Athens?

Athens is the capital of Greece and is a city full of history and culture. While it might be most well-known for hotspots like its ancient ruins of the Acropolis, it has an important coastline. The Attic Peninsula houses Athens, surrounded to the east and south by the Aegean Sea. This place by the coast has rendered it very significant in its development, both in ancient times as a large trading and naval power center and nowadays as a busy port city and a favorite tourist destination.

Geographically, the city spreads out from the coastal plain, with the Saronic Gulf to the southwest and the Aegetus proper to the southeast. The coastline around Athens is a mix of urbanized areas, marinas, and small beaches. The Piraeus is among the biggest Greek ports, a leading hub for passengers and cargo, connecting the city of Athens with the whole world. The city's skyline, with a combination of ancient ruins, modern high-rise buildings, and the nearby mountains at Mount Hymettus and Mount Penteli, add to its beauty.

Culturally, Athens is considered the cradle of democracy and Western civilization. Thousands of years of history, with influences from various empires and cultures, have shaped the city. The local people here have a strongly identifiable identity, well rooted with the sea. Fishing was their traditional occupation, and the maritime activities were always there to be inbuilt into the very economy of this city for survival. It is expected that the great variety of marine life will range from small fish species, which can live in shallow conditions, right up to the larger forms of marine mammals further out to sea.

2. What are the coastal currents like near Athens?

The coastal currents around Athens are due to a set of complex circumstances. The principal factor is the wind. There are different wind conditions in the Aegean Sea. The strong north-westerly wind during summer months is called meltemi. These can push surface waters inshore, creating an onshore current. Such onshore currents can carry nutrients from the open sea, adding to the nutrition of the local marine ecosystem and enabling plankton to grow, hence supporting a varied food web.

In turn, the southern winds can push the water offshore and form an offshore current. These winds may blow harder and longer in one place than in another, which makes the patterns of coastal currents change. The tides have also contributed, though their amplitude in the Aegean Sea is comparatively small. The ebbs and flows of tides interact with wind -driven currents. During high tide, the water might flow in a different direction or at a different speed compared to low tide, affecting the overall dynamics of the coastal currents.

The bathymetry of the region is another important factor. The seabed around Athens is an irregular topography with underwater valleys, ridges, and reefs. These characteristics can speed up, slow down, or deflect such currents. For example, a narrow submarine channel can constrict the current and increase the velocity of water while a big reef can work as a baffle and alter the direction. The river discharge from the few small rivers also will impact on the coastal current. Although the volume of freshwater input may not be as large as in some other regions, it can still change the density of the seawater, creating density - driven currents that interact with the existing wind - and tide-driven currents.

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

Surface Drifting Buoy Method

The surface-drifting buoy method is one of the simple and convenient methods of observation of surface level currents. Small buoys with GPS trackers are set into the water. Carried by the currents, the movement of the buoys is followed over some time. Scientists from the buoy trajectory can estimate the speed and direction of the movement of surface currents. However, the method has shortcomings. This in turn causes them to be laterally moved away from the path of actual current. This technique also shows the surface layer, not the deep - layer, water currents.

Anchored Ship Method

An anchored ship can serve as a fixed platform for the current measurements. The current meters are suspended from it at various depths. These meters can record the velocity and direction of the currents at each depth. The method allows the collection of detailed data on the vertical profile of the currents at a given location; however, it is limited in area coverage. It is representative only of the area immediately around the ship, and the presence of the ship itself can potentially disrupt the natural flow of the water.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP current meter has become a preferred method for measuring coastal currents near Athens. ADCPs use sound waves to measure the velocity of water at multiple depths simultaneously. These may be deployed from ships, moored to the seabed, or attached to buoys. This gives a greater possibility for data acquisition. ADCPs are less disturbed by surface level disturbances like wind and, thus, more correctly measure the current condition. It provides in detail, a three-dimensional view of the current structure including horizontal and vertical flow components.

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

ADCPs basically work on the principle of the Doppler effect. When an ADCP current profiler sends high-frequency sound waves into the water, those sound waves are reflected back by small particles in the water, such as plankton, sediment, or tiny bubbles. The scattered sound waves arriving at the ADCP have a different frequency than that of the emitted waves. This frequency shift-the Doppler shift-is proportional to the velocity of the particles (and thus the water) relative to the ADCP.

Most ADCPs have multiple transducer beams. From each beam, the measured Doppler frequency shift can be interpreted by the ADCP to find the velocity components of the water along different directions. The ADCP then calculates the vector addition of these velocity components to find the three-dimensional velocity of the water. This helps describe in complete detail exactly how the water is moving in all directions; this, again, is quite vital to get an accurate mapping of the coastal currents.

5. What do high quality current measurements in the coastal area of Athens demand?

Equipment Material Reliability

The material to be used for the casing will determine whether the measurements obtained from the ADCP profiler are of high quality or not. Ideally, the casing should be made from Titanium alloy. The resistance of this metal to corrosion is excellent and suitable for this equipment given that it will always be exposed to the constant corrosive sea water. It can also resist degradation for extended periods under salty conditions and thus will keep the ADCP functional and running for a long period. Its high strength-to-weight ratio also means that even under strong currents, it or rough seas, the ADCP will retain its structural integrity.

Size, Weight, and Power Consumption

The ADCP flow meter should be small in size and lightweight. Compact design allows easier deployment in any environment. It can easily be installed on a small research vessel or a buoy. The flow field that will be measured would also have lesser disturbance. One very important feature is the low power consumption of the ADCP. It would allow longer time for its running without changing batteries or having it connected to a power source outside. This is especially important for long - term deployments in the coastal areas around Athens.

Cost-effectiveness

ADCP meter should be as economical to the extent that wide-scale, holistic monitoring of coastal currents around Athens is realized, meaning, not only does one research institution become capable but the number increases within environmental monitoring groups and also through local initiatives with the urge and determination to do more by providing further assistance toward the mission of collecting data towards a holistic, comprehensive understanding of the dynamic current.

6. How to Choose the Right Equipment for Current Measurement?

According to the Purpose of Use

• Shipborne ADCP: A moving ship-mounted ADCP. This will be ideal to undertake the large-scale survey of the coastal currents. While the ship moves along the coast continuously, the shipborne ADCP measures the currents to provide a broad-scale view on current patterns over an area. It is useful in initial research or to study how the currents change in a wide geographical range.
• Bottom-Mounted ADCP: These are placed on the seabed and are used for long-term, fixed-point monitoring. They can provide continuous data on the currents at a specific depth and location. This is valuable to understand the local hydrodynamics, such as how the currents behave in a particular bay or near a specific underwater feature.
• Buoyant ADCP: Buoyant ADCPs are attached to a floating buoy and thus can move with the surface currents. They are well-suited for monitoring the surface and near-surface current patterns. They can be deployed in order to track the movement of water masses over time. This is important for knowing how nutrients, pollutants, or marine organisms are transported.

Based on Water Depth

• The 600kHz ADCP should be sufficient for water depths within 70m. The increased frequency of the sound waves means that more can be measured within shallower waters. It has a high-resolution current structure data, which could easily detect the small-scale variations in currents.
• A 300kHz ADCP will be good for water depths of about 110m. It gives a balance between the measurement range and resolution. It can penetrate deeper into the water column compared to a 600kHz ADCP while still providing relatively accurate measurements for mid-depth coastal waters.
• In deeper waters up to 1000m, the 75kHz ADCP would be recommended, as the lesser frequency of sound waves can pass deeper, while resolution may not be as good as higher frequency ADCPs would provide. For this reason, it is good for measuring the currents in deeper parts of the Aegean Sea near Athens.

There are several well-known ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. However, for those seeking a cost-effective yet high-quality option, the China Sonar PandaADCP is a great choice. Made of all-titanium alloy, it offers excellent durability and performance at an affordable price. It is an economic-class ADCP that provides great value for money. You can find more information about it on their official website: (https://china-sonar.com/).

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