How we can measure coastal currents of Lobito?

1. Where is Lobito?

Lobito is a lively seaport town located in western Angola on the shores of the South Atlantic Ocean. It is an important port city and a key economic hub in the region. Its location has made it a crucial focal point of commerce, and its new port facilitates the exportation of numerous products, such as oil, minerals, and agricultural produce.

The cityscape of Lobito is a mix of contemporary infrastructure and indigenous Angolan architecture. The city center itself is alive with activity, replete with seafood markets, handicrafts, and everyday staples. The populace is diverse and dynamic, the population having an innate connection with the sea. Fishing is a significant economic activity but also forms part of the traditional culture, as generations of fishermen have relied on the marine resources.

Geographically, Lobito is situated in a setting where the waters along the coast are determined by an interplay of factors. The proximal continental shelf with different width and depth plays a role in defining the conditions at sea. The seafloor south of Lobito is composed of sandy plains, rocky outcrops, and submarine canyons and provides habitats for a variety of marine life. From coral reefs with their colorful hues to shoals of fish, the marine ecosystem in the region is diverse and productive.

2. How is the condition of the coastal currents off Lobito?

The coastal currents off Lobito are dominated by a number of interacting factors. Tides are a significant force, and the region experiences semi-diurnal tides. These tides increase and decrease the sea level twice a day, creating strong tidal currents that flow in and out of the bays and along the coast. Water rushes in to the coastal areas at high tide and back out at low tide, carrying sediment and nutrients with it. These tidal currents can also potentially significantly affect the marine ecosystem in the region, shifting the distribution of aquatic life and erosion pattern along the coast.

The oceanic circulation on the broader scale also plays its part. Lobito's coastal waters are influenced by the Benguela Current system, though its influence is less strong than in areas further south. The Benguela Current is composed of cold, nutrient-rich water, which upwells to the surface and maintains a vibrant marine ecosystem. In Lobito's waters, however, the nature of the current may be altered by local topography and other factors.

Wind is another major factor influencing coastal currents. Seasonal variations may occur in prevailing winds in the region. During certain seasons, there are strong onshore winds that force surface waters, creating wind - driven currents. These winds can accelerate surface - level flow and reverse its direction, interacting with tidal and oceanic flows to produce complex flow patterns. The coastline of Lobito, composed of inlets, headlands, and bays, further deforms these currents, leading to areas of eddies and upwellings.

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

Surface Drift Buoy Method

One of the conventional means of observing Lobito's coastal water flow is the use of surface drift buoys. Surface drift buoys are equipped with GPS tracking devices. Once they are tossed into the ocean, they are moved about by the surface currents. The researchers can determine the direction and speed of the currents at the surface level by monitoring the movement of the buoys over time with the aid of GPS data. However, there are some limitations to this. It only provides data on the surface layer of the water column and is subject to significant wind-driven motion, which may not represent the true underlying flow of current. Surface drift buoys also can easily be pushed out of place by heavy seas or strong currents, reducing the quality of the data, especially in the more energetic waters near the port and along the open coast.

Moored Ship Method

The ship moored technique is the method where a ship is anchored in a fixed position near the Lobito coast. Current-measuring instruments such as current meters are dropped from this ship at varying depths. The speed and direction of the current at each depth are measured using these instruments, allowing for the construction of a vertical profile of the current. While this technique will yield detailed data at a given moment, the spatial reach is limited to around the anchored vessel. Further, the presence of the ship itself might interfere with the natural flows in the area, and readings would be confounded by movement of the vessel and by agitation from its engines.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is today a more advanced and affordable way of assessing coastal currents in Lobito. ADCPs are quite popular in oceanographic research because they can measure current velocity at different depths simultaneously across a wide volume of water. This technology allows the researchers to get a full picture of the three-dimensional configuration of the existing current that is required in order to precisely simulate the complex coastal circulation process in Lobito's waters. Compared to traditional methods, ADCPs allow for easy and accurate measurement of currents in different depths in a short period of time and provide valuable information about how currents vary vertically and horizontally and also how they interact with the area topography.

4. How do ADCPs operating on the Doppler principle work?

ADCPs work on the principle of the Doppler effect. The device emits acoustic signals, or sound waves, into the water column. As these sound waves interact with suspended small particles in the water, such as plankton, sediment, or bubbles, part of the sound energy is bounced back towards the ADCP flow meter. When the particles are carried by the current, the scattered sound waves will have a frequency different from the radiated wave frequency. The Doppler shift, which depends on the particles' speed, and consequently the current speed, is directly proportional to it.

Most ADCPs possess a few transducer beams, typically three or four, which are aimed at different angles. By measuring the Doppler shifts in each beam, the ADCP can calculate the components of the current velocity in three-dimensional space. The instrument divides the water column into individual depth bins, and for every bin, it calculates the current velocity. This method allows ADCPs to generate a high-resolution velocity profile of the current with depth and a wealth of information about the water flow in the coastal waters of Lobito. For example, it is capable of showing how the velocity of the current changes from the surface, which is wind-controlled, to the more subsurface layers that are oceanic circulation-controlled, and how these changes differ from area to area of the coastline.

5. What is necessary for high-quality measurement of Lobito coastal currents?

High-quality measurement of Lobito's coastal currents requires the measuring equipment to meet several vital requirements. Material reliability is the most important since the equipment will be exposed to the aggressive marine environment. Lobito's coastal waters are highly corrosive salt water, and equipment also has to be able to withstand the mechanical wear of wave action and biofouling. Equipment materials from which ADCPs have to be made must be highly resistant to these.

The equipment must be made as compact as possible so that its influence on the free flow of current is minimized and to allow it to be deployed with ease at various points, e.g., shallow waters off the coast and deeper channels in the open sea. Lightweight equipment is also preferred, as handling while deploying and recovering is easy, especially under the crowded port environment of Lobito and rough open-sea conditions. Low power consumption is paramount, especially for use in the field for extended durations since in some uses, the availability of power sources may be limited.

Cost-effectiveness is the second vital factor, especially where massive measurement is required. Expensive machinery will limit the number of instruments one can use to take measurements because the range of space the measurement covers will be constrained due to the limitation by economic considerations. Titanium alloy housing on ADCPs will be an excellent choice. Titanium alloy offers superior saltwater corrosion resistance and can withstand the harsh marine environment. Titanium alloy is also robust and light in weight, suitable for ship - mounted and buoy - mounted use. Although a high - performance material, advancements in manufacturing have made titanium alloy - cased ADCPs less expensive, rendering them a reasonable option for large - scale coastal current monitoring in Lobito.

6. Selecting Proper Equipment for the Measurement of Currents?

Proper equipment to be employed to measure currents in Lobito would vary according to application.

ADCPS Categorized Based on Usage

• Ship - mounted ADCP: Mounted onboard a ship, this kind of ADCP may be best applied to the wide - range Lobito coastal water surveys. When the vessel passes through the region, the ADCP can continuously monitor the currents along its trajectory and provide a large-scale description of the currents caused by tides, wind, and oceanic circulation. This can be used in operations such as marine navigation, ascertaining the general circulation of the waters of a region, and fishery management, as it would allow the identification of areas with dense concentrations of fish.
• Bottom-mounted (Sit-on-the-bottom) ADCP: These ADCPs are mounted on the ocean floor and are used for long-term, fixed-point measurements. They stay in one position for long periods of time, gathering information on currents at a particular point. This type of ADCP is useful in investigating the local, fine-scale current processes, e.g. the effect of underwater features on the flow of the current and temporal changes in current patterns. This information is significant in ecological investigations, environmental monitoring, and determining the impact of human activities, such as port operations, on the marine environment.
• Buoy-mounted ADCP: Mounted on a floating buoy, such ADCPs are free to follow the current and drift along with it, taking the velocity at several depths as it drifts. They are particularly useful for monitoring large-scale synoptic current structures of the open sea off Lobito or the motion of oceanic circulation controlled water masses over a large extent. This ADCP is able to provide valuable information for predicting the dispersion of pollutants, marine species migration, and the overall health of the marine ecosystem.

Selection of Frequency

The ADCP frequency should be chosen wisely relative to the depth of the water. A 600kHz ADCP would be suitable for waters up to a depth of around 70m, providing high-resolution measurements in comparatively shallow waters along the Lobito coastline. For depths of approximately 110m, a 300kHz ADCP would be appropriate, as it allows the acoustic signals to penetrate deeper within the water column but still has reasonable measurement accuracy. In very deep water, up to 1000m, a 75kHz ADCP is the one that is typically used. For Lobito's coastal waters, where the typical water depth would be less than 1000m, a 600kHz or 300kHz ADCP would most likely be required for most measurement requirements.

There are many well-known brands of ADCP in the market, i.e., Teledyne RDI, Nortek, and Sontek. Nonetheless, for cheap but high-quality ADCPs, the ADCP manufacturer China Sonar's PandaADCP is the best choice. Made of pure titanium alloy, it delivers superior performance and longevity at a very affordable cost. Being a low-cost ADCP, it is a perfect option for researchers, local fishermen, and environmental monitoring departments who are concerned with accurately computing the coastal currents of Viña del Mar. To know more, visit https://china-sonar.com/.

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