How do we measure Kourou's coastal currents?

1. Where is Kourou?

Kourou is a coastal town on the French Guiana coast on the Atlantic Ocean. It is located near the mouth of the Sinnamary River, which is the region's main river. The outflow of the Sinnamary River into the ocean heavily influences the coastal ecosystem around it. Kourou is geographically bounded by dense rainforests and thus is an interesting mixture of terrestrial and marine ecosystems.

The town is full of history. The region was inhabited by indigenous people a long time before the arrival of European settlers. French settlers arrived in the region in the 17th century, settled, and introduced new agriculture and trading methods. Kourou is best known today for being home to the Guiana Space Centre, one of the world's top spaceports. The space centre has brought international attention to the town and also economically benefited the town.

The Kourou coastline comprises diversified land features that are constituted by sandy shores, mudflats, and extensive mangrove forests. Besides being an ecological balance stabilizer, the mangrove forests form a natural buffer against erosion in the coastal areas. They support diversified terrestrial and marine fauna from fish and crustaceans to diverse birdlife.

2. How are the coastal currents off Kourou?

The coastal currents off Kourou are characterized by a complex interaction of a variety of influences. One such significant control is the Sinnamary River mouth. The vast volume of freshwater discharges into the Atlantic Ocean and creates a plume. This plume influences the coastal water density and salinity and creates a distinct coastal current separate from the other oceanic currents surrounding it. Depending on the flow rate of the river, which in turn depends on the seasonal rainfall over the Sinnamary River catchment, the shape and dimensions of the plume may differ.

Atlantic Ocean tides also have their part to play. Semi - diel tidal activity produces periodic changes in water level. Spring tides have the increased moon and sun gravitation, leading to stronger tidal currents. The tidal currents encounter and interact with the river - plume current and influence the resulting motion of coastal waters.

Prevailing winds in the region push surface waters towards the west and are mostly the northeasterly trade winds. The wind-driven current merges with the river-plume current and tidal currents. The mix generates a complex water flow pattern. The sea bottom bathymetry, with its uneven depths and sea bottom features such as sandbars, channels, and reefs, contributes to the complexity of the coastal currents as well. These bottom characteristics may either direct or disperse the currents' flow, producing eddies and other complex flow structures.

3. How to observe Kourou's coastal water flow?

Surface Drifting Buoy Method

Surface drifting buoy method is a traditional method of observing coastal water flow. Scientists release tracking devices-equipped buoys into the sea. By monitoring the displacement of buoys over time, they are able to establish the direction and velocity of the surface currents. This method is not without its limitations, however. It requires that they only be told the information about the surface layer of the water column, and the buoys are extremely prone to wind disturbance. Wind has the tendency to make the buoys move in a direction that is not necessarily true reflection of the direction of movement of the underlying currents.

Moored Ship Method

In the moored ship method, there is a ship that is moored and utilized as the platform for measurement of currents. The equipment is dropped off the ship to measure the flow of water at different levels. Though the method can record high-resolution vertical profiles of the currents, it is prone to several disadvantages. The coverage is limited to the area in the vicinity of the moored ship, and the ship's presence can interfere with the natural movement of the water, thus affecting the quality of the measurement. Assisting a ship over an extended period is also logistically challenging and costly.

Acoustic Doppler Current Profiler (ADCP) Method

ADCP profiler is now an evolving and improved method of measuring coastal currents. ADCPs have the ability to monitor water currents at a broad range of height through high-resolution detail of the velocity profile of the water column. ADCPs are able to be installed on an array of different platforms, i.e., on ships, on buoys, or even on the ocean floor. Shipboard ADCPs are able to make continuous measurements while the ship is moving, charting a large region in a short period of time. Bottom-mounted ADCPs can also provide long-term, fixed-point measurements, allowing scientists to study long-term trends in the coastal currents.

4. How do ADCPs based on the Doppler principle function?

ADCPs operate on the Doppler principle. ADCPs transmit acoustic pulses into the water. The pulses bounce back from suspended particles such as sediment, plankton, or bubbles in the water. When the water is moving, the frequency of the returning pulses also shifts. From this shift in frequency, the ADCP current profiler can calculate the water velocity relative to the instrument.

Most ADCPs possess multiple transducer beams, typically four or more, that are pointed in different directions. The multi-beam configuration enables the determination of the three-dimensional water velocity. Through the combining of the signals from the different beams, the ADCP can create a comprehensive picture of the current velocity at different depths of the water column. Data collected by the ADCP can be processed in real - time or stored for later analysis, showing the dynamics of the coastal currents.

5. What's needed for high - quality measurement of Kourou coastal currents?

In order to obtain high - quality measurement of Kourou's coastal currents, the measuring equipment should possess some significant qualities. It should be made of rugged materials, small size, low weight, low power, and low cost. These characteristics allow one to use a large quantity of instruments, which gives good spatial coverage.

ADCPS that are very appropriate are those having titanium alloy housings. Titanium alloy possesses excellent corrosion resistance that is essential for long-term exposure to the aggressive marine environment. It withstands the corrosiveness of seawater, thereby saving the inner mechanisms of the ADCP from damage. Titanium alloy is lightweight and strong and offers the strength and portability of the equipment. This enables accurate and long-term measurement of the coastal currents around Kourou.

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

Selection Based on Use

ADCP selection is done according to its use. For ship-borne measurements, ship-mounted ADCPs are ideal. They can provide real-time information while the ship is moving through the water in a large area in a relatively short period of time. For long-term monitoring at a fixed point, bottom-mounted ADCPs are preferable. They can yield continuous information over a long duration, enabling researchers to investigate long-term trends in the coastal currents. Floating ADCPs are helpful for following the trajectory of water masses over vast regions, offering useful insights into large-scale circulation patterns.

Selection Based on Depth

The ADCP frequency also needs to be considered in relation to water depth. For water depths of less than 70m, 600kHz ADCPs would be appropriate. They can provide high - resolution measurements in shallow water. For water depths up to 110m, 300kHz ADCPs would be appropriate. For deeper waters, up to 1000m, 75kHz ADCPs would be the best option.

A few of the best ADCP brands in the market are Teledyne RDI, Nortek, and Sontek. However, for those on a budget, the ADCP supplier China Sonar's PandaADCP is highly suggested. Made entirely of titanium alloy, it offers excellent performance at low expense. It's an excellent choice for users on a budget who still require reliable ADCPs for coastal current measurement. You can find out more about them on their official site: https://china-sonar.com/.

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