How do we measure Barreirinhas coastal currents?

1. Where is Barreirinhas?

Barreirinhas is a municipality in the north-east state of Maranhão, Brazil. It shares a border with the Atlantic Ocean, in the center of the Lençóis Maranhenses National Park. This unique geography situates Barreirinhas in the intersection of land, sea, and vast coastal dune ecosystem.

Geologically, the area around Barreirinhas is characterized by gigantic sand dunes, some of the largest in the world. The dunes extend hundreds of miles along the shoreline, a beautiful sight to behold. In between the dunes, there are numerous lagoons that link with the sea, making for a water labyrinth. The shore itself has an assortment of sandy beaches, rock outcrops, and small estuaries. They help to maintain mangrove forests, which help to maintain the local ecosystem. They are nurseries for a great variety of fish and crustacean fauna, clean the water by filtering out pollutants, and help stabilize the shore against erosion.

Barreirinhas has a vibrant history. The area was initially occupied by native peoples, and their influence is still evident in local traditions, art, and mythology. Portuguese colonizers arrived in the area during the 16th century and brought with them new agricultural and trading practices. Over time, Barreirinhas developed into a small but vibrant seashore town, with fishing and tourism its main sources of revenue.

2. How is the condition of the coastal currents close to Barreirinhas?

The off-shore currents off Barreirinhas are shaped by a complex interaction of many variables. One of the world's largest ocean currents in the Atlantic Ocean, the North Brazil Current, is a significant contributor. This west-flowing, warm current flows into Barreirinhas, interacting with local topography and bathymetry. As it arrives on the coast, it can divide into smaller streams, creating a complex pattern of coastal currents.

Atlantic Ocean tides are also of great significance. The semi-diurnal tidal regime generates periodic variations in water level. Spring tides experience greater gravitational pull of the moon and sun, causing greater tidal currents. These tidal currents interact with the North Brazil Current and with the coastal geometry, which controls the general water movement along the coast.

The unique topography of the coast of Barreirinhas, lagoons and sand dunes, also determines the coastal currents. The dunes act as natural screens and alter the path of water flow. The ocean-tied lagoons hold and release water based on the tide, which makes it even harder to anticipate current trends. The seabed bathymetry, varying depths and topography of the sea floor such as sandbars, channels, and reefs, also plays a role in the dynamics of the coastal currents. Underwater features will either channel or disrupt the flow of the currents.

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

Surface Drifting Buoy Method

The surface drifting buoy method is a traditional method of observing coastal water flow. Scientists deploy buoys carrying tracking devices into the water. They can determine the direction and speed of the surface currents by monitoring the path of these buoys over a period of time. This method is not ideal, however. It only informs them regarding the surface layer of the water column, and the buoys are extremely susceptible to wind disturbance. The buoys are susceptible to deflection by the wind and may therefore make movements that are not representative of the actual movement of the currents on the underlying surface.

Moored Ship Method

The moored ship method employs a ship moored as a platform for the measurement of currents. Instruments are lowered from the ship to measure the water flow at various depths. While the method is able to measure exact vertical profiles of the currents, there are several disadvantages. The spatial range is limited to the area around the ship at anchor, and the presence of the ship can disrupt the natural flow of the water, thus distorting the accuracy of measurement. In addition, maintaining a ship in anchor position for an extended period could be logistically problematic and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP meter has been discovered to be a more advanced and less expensive device to utilize when measuring coastal currents. ADCPs can observe water currents over a broad vertical range and deliver high-resolution information regarding the velocity structure of the water column. They are deployable on numerous platforms, ranging from ships and buoys to the seafloor. Ship-mounted ADCPs have the ability to record data continuously as the ship travels, scanning a broad area in a comparatively short period. Bottom - mounted ADCPs can make fixed - point, long - term measurements, allowing researchers to study long - term trends in the coastal currents.

4. How do Doppler principle ADCPs work?

ADCPs employ the Doppler principle. They emit acoustic waves into the water. The waves are reflected off suspended particles such as sediment, plankton, or water bubbles in the water. Since the water is in motion, the frequency of the reflected wave changes. This frequency change is detected and employed by the ADCP profiler to calculate the speed of the water relative to the instrument.

Most ADCPs contain several transducer beams, typically four or more, at different angles. This multi-beam configuration allows the detection of the three-dimensional velocity of water. By combining the signals of these beams, the ADCP is able to create a complete image of the current velocity at different levels in the water column. The data collected by the ADCP can be calculated on - line or stored for post - analysis, providing valuable information in terms of dynamics of coastal currents.

5. What does high - quality measurement of Barreirinhas coastal currents require?

For precise measurement of Barreirinhas's coastal currents, the measuring instruments should have some key characteristics. They should be made of robust materials, be of small size, lightweight, low power, and inexpensive. These qualities enable one to deploy a large number of instruments, enabling good spatial coverage.

ADCPs with titanium alloy housings are highly recommended. Titanium alloy has good corrosion resistance, required for long-term deployment in the harsh marine environment. It resists the corrosive effect of seawater, preventing damage to the internal ADCP components. Titanium alloy is lightweight and also has high strength, which makes the instrument robust and portable. The characteristics facilitate accurate and long-term measurement of coastal currents around Barreirinhas.

6. Selection of the suitable equipment for measurement of current?

Choice Based On Application

ACDP choice is based on its application. In ship-borne surveys, ship-mounted ADCPs are optimal choice. They have the ability to provide real-time data while the ship traverses the ocean, covering an extended area within a relatively brief span of time. For long - term monitoring at a location, bottom - mounted ADCPs are used. They are able to provide continuous data over an extended period of time, allowing one to view long - term trends in the coastal current. Floating ADCPs are useful for tracing movement of water masses over long distances and providing useful information on large - scale circulation patterns.

Depth - dependent selection

The depth of water should also be considered in deciding the ADCP frequency. For water depth less than 70m, 600kHz ADCPs would be appropriate. They are able to measure at high resolution for shallow water. For a maximum depth of 110m, 300kHz ADCPs can be utilized. For greater depths, up to 1000m, 75kHz ADCPs would be the better option.

There are some popular ADCP brands in the market, including Teledyne RDI, Nortek, and Sontek. Nevertheless, for those who are looking for budget - friendly options, the ADCP supplier China Sonar's PandaADCP is greatly recommended. It is made of pure titanium alloy and provides great performance with a low price. It is a great option for users who are budget - friendly but still need quality ADCPs for coastal current observation. For further details, go to their official website at: https://china-sonar.com/.

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