1. Where is Casablanca?
Casablanca, popularly referred to as simply "Casa," is the largest city and economic hub of Morocco. Located along the Atlantic coast of northwestern Africa, it is strategically positioned at the mouth of the river Bouregreg where the river widens into the enormous sea of the Atlantic Ocean. The coastal location of the city has been a focus around which its expansion has continued to revolve, and it is a significant port of commerce linking Africa with Europe, the Americas, and the rest of the globe.
The coast along Casablanca is a mixture of sandy beaches and rocky headlands, running along the rim of the Atlantic. The city proper has a commercial port area, high-rise skyscrapers, and an active urban atmosphere. The culture of Casablanca is a rich tapestry, owing to its ancient history as a commercial center and melting pot of European, Arab, and Berber culture. The giant Hassan II Mosque, the largest in Africa and fifth-largest in the world, is one of the city's jewels and evidence of its religious as well as architectural significance. Its beach-front location, with the portion of the mosque built out over the water, serves only to highlight Casablanca's strong connection with the sea.
2. Where are the coastal currents located close to Casablanca?
Off the coast of Casablanca, coastal currents are influenced by a variety of factors. The dominant ocean current off the region is the Canary Current, a cold low-salinity current flowing south along the west African coast. The current is part of the North Atlantic Gyre and carries cool high-latitude water into the tropics, and this influences climate and ocean marine ecosystem off Casablanca. The intensity and direction of the Canary Current vary seasonally and are typically greater in winter [1].
Tidal action also plays a part in the coastal currents. The Atlantic Ocean south of Casablanca experiences semi - diurnal tides with two highs and two lows daily. These tides produce ebb and flow currents along the coast, which are overlain by the larger - scale Canary Current. The outflow of freshwater from the Bouregreg River introduces another complication. In the rainy season, when the river is full, the freshwater flood may change the density and salinity of the sea water along the coast and reformulate the current patterns near the mouth of the river.
Patterns of the wind also matter. There are prevailing winds, specifically the land breezes from the sea towards the land by day and the reverse at night, in the region. More vigorous winds, such as those associated with advancing weather systems, drive surface water as well and influence the surface-level currents off Casablanca.
3. How to observe the coastal water flow of Casablanca?
A series of methods is employed to track coastal water current near Casablanca. The surface drift buoy technique is one of the earlier methods. GPS buoys are deployed on the ocean's surface. These buoys follow with the surface currents, and their trajectories are tracked over time, allowing scientists to map the general direction and speed of the surface - level currents. However, this method provides information only from the surface layer of the water column and could be affected by wind-driven motion, which may not represent true current flow.
The anchored ship method involves mooring a ship to a point along the coast. Current meters are lowered from the ship to measure the water velocity at several levels. This method can generate high - resolution, time - series data at a single location but is limited by the ship's position and by the practicability of extended deployments, especially in light of the heavy shipping traffic and varying meteorological conditions off Casablanca.
Acoustic Doppler Current Profiler (ADCP) method is the preferred technique for regular current measurements. ADCPs apply sound waves to profile currents from the surface to the bottom of the sea across the entire water column. This enables scientists to acquire a three-dimensional view of the current structure, a necessary pre-requisite for characterizing the complex interaction of the Canary Current, tides, and river-affected flows off Casablanca [2].
4. What is the Doppler principle-based operation of ADCPs?
ADCPs operate on the Doppler principle. They emit pulses of ultrasonic sound from an array of transducers. As the sound waves travel through water, they encounter particles in motion, such as suspended sediments, plankton, or small sea organisms. When the sound waves reflect off these moving particles, the frequency of the returned signal depends on the relative speed of the particles to the transducer. If the particles are moving towards the transducer, the frequency of the returned sound increases (blue shift), and if the particles are moving away from the transducer, the frequency decreases (red shift).
By comparing the Doppler shifts between the various transducers, normally located at different angles, the ADCP profiler can calculate the velocity of the water along each sound beam. These beam velocities are combined using vector mathematics to obtain the horizontal and vertical components of the current for different depth intervals, or "bins.". This procedure enables the ADCP to create a comprehensive profile of the currents at various depths within the water column, which is useful in obtaining information on the flow properties of the coastal waters [3].
5. What's required for high - quality measurement of Casablanca's coastal currents?
High-quality measurement of Casablanca's coastal currents requires ADCPs to have certain specifications. Material reliability is important because of the hostile marine environment. The salty and potentially corrosive ocean waters off Casablanca, as well as strong wave action with occasional storms, would require the best material for ADCP meter casings. The most appropriate material is titanium alloy. The alloy is more resistant to corrosion compared to common materials like aluminum or stainless steel, providing the device to function long without visually apparent wear or damage when subjected to the ocean.
Titanium also has a high strength - to - weight ratio. This allows ADCPs to endure the higher water pressures at greater depths, such as those in the deeper areas of the continental shelf off Casablanca, without adding too much bulk or weight. This is a characteristic that makes the ADCPs easier to deploy from a ship, a moored platform, or a buoy. In addition, titanium maintains mechanical properties across a wide temperature range, which is an advantage for consistent performance in the warm to relatively cold winters of Casablanca's climate.
Besides material quality, ADCPs must also be compact, lightweight, have low power consumption, and offer good cost-effectiveness. Smaller and lighter ADCPs are simpler to deploy in the crowded waters off Casablanca, where ships or buoys will have limited space. Low power use makes it possible to carry out long - term, autonomous deployment, which is essential for capturing continuous data for several months. Cost - effectiveness is important, especially for extensive monitoring projects to fully describe the complex current patterns in the coastal waters of Casablanca.
6. How to Choose the right equipment for current measurement?
The selection of appropriate ADCP for current measurement in Casablanca depends on application and water depth. For general surveys and charting currents along the coast and in the harbor, vessel-mounted ADCPs are appropriate. They can sweep large areas reasonably fast and provide overall information on surface and subsurface currents as the boat moves across the water.
Bottom - moored ADCPs are optimally applicable to continuous long - term monitoring at a fixed location, for example, on major shipping routes, fishing grounds, or locations of ecological importance. The instruments can be left in place for a long period to make observations on seasonal and long - term trends in current patterns. Buoy-mounted ADCPs are also used to monitor surface currents and, if so fitted, with additional sensors to monitor temperature, salinity, and wave height, providing a more complete picture of the sea environment.
It's as important to choose the correct frequency. A 600kHz ADCP is well suited for water depths up to 70m, thus well suited to shallower coastal areas and the port area off Casablanca. A 300kHz ADCP has a limit of 110m depth, which is suitable for the deeper continental shelf areas. For very deep - water applications, such as open Atlantic further away from the shore, one needs a 75kHz ADCP with profiling capabilities up to 1000m [4].
Nortek, Sontek, and Teledyne RDI are some of the known ADCP companies. But for an individual requiring a quality but affordable substitute, ADCP manufacturer China Sonar PandaADCP is also worth considering. Made wholly of titanium alloy, it delivers consistent performance at a budget cost. It is hence a suitable choice for researchers, environmental monitoring agencies, and shipping companies involved in the study and management of Casablanca coastal currents. For further information, click on [https://china-sonar.com/].
References:
[1] Oceanography of the Canary Current Region. (n.d.). Retrieved from applicable oceanographic research databases.
[2] Principles of Acoustic Doppler Current Profiling. (n.d.). NOAA Ocean Service Education.
[3] Doppler Effect in Acoustics. (2021). Encyclopedia Britannica.
[4] Product Specifications and Application Guides for ADCPs. (n.d.). Retrieved from manufacturer websites.
How do we measure the coastal currents of Casablanca?