How do we measure Maceió's coastal currents?

1. Where is Maceió?

Maceió, Brazil's capital for the state of Alagoas, is located on the north-east coast of Brazil in the Atlantic Ocean. Approximately 9°40′S 35°42′W, the position of Maceió is quite good as a coastal settlement. The city boasts renowned beaches by which Maceió is renowned worldwide as a tourist town. The beaches are not merely an essential tourism component, but also of aboriginal ecology.

The geologic setup here in the area around Maceió consists of low lying in the coastal region and ancient sediments. The sea floor off this coast was also complex in the same way in terms of bathymetry due to irregular sea floor as well as numerous other hundreds of underwater features such as coral reefs and channels. The coral reefs are also important because they provide a diverse variety of marine fauna and contribute significantly to the coastal currents. The city is also influenced by the nearby São Francisco River, whose freshwater output into the sea affects the coastal salinity and water density.

Maceió is a diversified and rich city in terms of history. The Tabajara natives and other natives populated the area first. Portuguese conquerors found the region during the 16th century and established a town that expanded into the city of Maceió. Events like Portuguese domination, slave trade, and establishment of Afro-Brazilian culture left their impressions in the city for all these years. Maceió's economy is presently supported by an assortment of industries such as tourism, industry, and services.

2. How is the status of the coastal currents around Maceió?

There are a variety of controlling factors in the coastal region of Maceió that interact with each other and influence the coastal currents. A few of the controlling factors are the South Equatorial Current, which is a primary ocean current of the Atlantic Ocean. The South Equatorial Current is a westward-flowing current containing warm water that moves along the coast of Brazil. As it runs around the area in front of Maceió, it interfaces with the local bathymetry and topography. The South Equatorial Current breaks up into many small branches along the coast, creating an intricate coastal current regime.

Tides from the Atlantic Ocean dominate. The semi-diurnal tidal cycle creates distinctive water-level changes. Spring tides have more energetic tidal currents due to the greater gravitational attraction of sun and moon. Tidal currents combine with the South Equatorial Current and coastal shape, guiding the overall direction of coastal water. The tides also contribute to the generation of rip currents, narrow powerful streams flowing out from the coast. Rip currents are dangerous to swimmers and are an option for consideration at the coast.

Region-wide prevailing winds, the northeasterly trade winds particularly, guide the coastal currents. These winds are able to push the surface waters in a specific direction, therefore creating a wind-driven current. The wind-driven current is mixed with the South Equatorial Current and tidal currents, and the water movement pattern becomes more complex. Bathymetry in the seafloor surrounding Maceió, for example, coral reefs, sandbars, or channels, may deflect or disperse the current movement. For example, coral reefs create a barrier to deflect the flow of water around them, but a channel attracts more current.

3. How to monitor Maceió coastal water flow?

Surface Drifting Buoy Method

Surface drifting buoy method is a classic technique for coastal water flow monitoring. Researchers throw tracking devices-mounted buoys into the ocean. By following the movement of buoys with time, they can figure out the speed and direction of surface currents. The method is limited, however. It only gives information on the surface layer of the water column, and the buoys are very vulnerable to wind interference. The wind will make the buoys oscillate in a direction that is not the true direction of movement of the underlying currents.

Moored Ship Method

The moored ship method consists of employing a moored ship as a platform for current measurement. Equipment is lowered from the vessel to measure the flow of water at different depths. Although this technique can yield precise vertical profiles of the currents, it has a number of disadvantages. The spatial resolution is restricted to the vicinity of the moored vessel, and the presence of the vessel may disturb the natural flow of water, which could impact the quality of the measurements. Furthermore, it is logistically complicated and costly to keep a ship moored for a long time.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP current profiler has proven to be a more sophisticated and effective instrument for the measurement of coastal currents. ADCPs can measure water currents over a wide vertical range, providing detailed information regarding the velocity structure of the water column. They can be mounted on different platforms, such as ships, buoys, and the seafloor. Ship - mounted ADCPs can take data continuously as the ship travels, hence it covers large areas in relatively short periods of time. Bottom - mounted ADCPs can offer long - term fixed - location measurements, enabling researchers to look into long - term trends of coastal currents.

4. How do Doppler principle-based ADCPs work?

ADCPs operate according to the Doppler principle. They emit pulses of sound into the water. The pulses bounce off suspended particles such as sediment, plankton, or air bubbles in the water. In flowing water, the frequency of the returning pulse changes. On sensing this frequency shift, the ADCP measures the water's velocity relative to the instrument.

Most ADCPs have numerous transducer beams, generally four or more, angled in many directions. The multi - beam configuration enables the ADCP to measure the three - dimensional velocity of the water. Processing the output from these beams, the ADCP can create a full image of the current velocity at multiple depths in the water column. The data obtained by the ADCP can either be analyzed immediately or stored to be analyzed at a later time, providing valuable information on the dynamics of the coastal currents.

5. What's required for high - quality measurement of Maceió coastal currents?

For high-quality measurement of coastal currents of Maceió, the measuring equipment must have quite a number of vital characteristics. It must be made from stable materials, of small size, low weight, low power, and of low price. All these characteristics allow the deployment of a large number of instruments with comprehensive spatial coverage.

It is highly recommended to equip the vessel with ADCPs having casings made from titanium alloy. Good corrosion resistance is ensured by the alloy, which is essential for long - term deployment within the corrosive marine environment. Being corrosion resistant to saltwater corrosive action avoids damage to the ADCP's internal parts. The alloy has adequate strength and lightweight, giving the instrument the durability and portability required. The obtained combination of attributes allows one to acquire precise and long - term measurements of coastal currents around Maceió.

6. Selecting appropriate equipment for current measurement?

Choice Based on Application

The selection of ADCP meter is based on its application. For ship-borne measurements, ship-mounted ADCPs are the best option. They can deliver real-time data while the ship travels across the water, surveying a large area in a short space of time. In the case of fixed point long-term observation, the bottom-mounted ADCPs are the most suitable. They can provide data continuously for a long period, and researchers can study the long-term trends in the coastal currents. Floating ADCPs can be used for the observation of the displacement of the water masses over large domains, as it yields valuable information about the large-scale circulation patterns.

Selection Based on Depth

The ADCP frequency must also be established based on the depth of water. For depths less than 70m, 600kHz ADCPs are appropriate. They can also provide high-resolution values for shallow waters. For depths up to 110m, 300kHz ADCPs are most appropriate. For deeper depths, up to 1000m, 75kHz ADCPs are most appropriate.

There are also several good-known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. But for economical people,the ADCP supplier China Sonar's PandaADCP is ideal. It is constructed entirely of titanium alloy for long-lasting performance at a low price. It is ideal for stingy users who nonetheless desire to possess reliable ADCPs for coastal current measurement. You may find out more about them on their official website: https://china-sonar.com/.

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