How to measure the coastal currents of Portugal?

1. Where is Portugal?

Portugal is an enchanting country on the Iberian Peninsula in southwestern Europe. It enjoys a varied geography along the Atlantic Ocean, with an impressive coastline that covers about 1,793 kilometers.

It is known for enchanting cities: from Lisbon, with its hilly, cobblestone streets, bright yellow trams, and ancient castles, to picturesque Porto, boasting of its port wines and medieval fascination. The people of Portugal are equally warm and hospitable, enriched with a vibrant culture deeply rooted in history, music, and deliciously mouthwatering cuisine.

Off the coasts of Portugal lay several important bodies of water. To the west is the wide Atlantic Ocean, which determines, to a large extent, the climate of the country as a whole and the coastline topography. Different types of oceanic currents cross off the coasts of Portugal and give rise to the existence of several types of fish and mollusk species. Then, of course, there are the bays and estuaries, such as the Tagus River estuary at Lisbon, also major areas of important habitats and areas for economic and ecological activity, such as fishing and shipping.

2. What is the situation of the coastal currents near Portugal?

Several factors determine the coastal currents around Portugal. The main influence comes from the large-scale circulation of the North Atlantic Ocean. The North Atlantic Current is a warm ocean current that yields waters in this area and may bring relatively warm waters along the coast of Portugal.

The shape of the coastline and seabed topography: an indented coastline with bays, capes, and underwater ridges may cause changes in direction and speed of the currents on either side of the headlands or underwater features; for example, the currents can accelerate and thus develop areas of stronger flow.

Weather conditions also affect the currents along the coasts. The prevailing winds, such as the westerlies, drive the surface waters and couple with the ocean currents below. Seasonal changes in temperature and precipitation can result in changes in the density of the water, thereby affecting the flow patterns of the coastal currents.

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

Surface Drifting Buoy Method

It is a technique in which buoys are set on the surface of the water, and these are left to drift in the currents. These buoys have tracking devices such as GPS, which can record their positions with time. The paths of buoy movements give information about the direction and speed of surface currents. It gives, however, mainly information about the surface layer and cannot therefore always provide an integral view of the whole water column.

Moored Ship Method

The ship is made fast in one position in the coastal area. By the use of instruments launched from the ship, the flow in the water at different levels is measured. This can give further details of the vertical profile of the currents near the mooring point. However, this has limitations for area coverage and measurement duration, as the ship is required to remain stationary for a considerably long period.

Acoustic Doppler Current Profiler (ADCP) Method

The ADCP has become a modern and comfortable means of measuring the coastal currents, using acoustic signals to measure simultaneously the velocity of water at different depths. This instrument can be deployed on ships, buoys, or even directly on the seabed, providing a wide range of applications, from which one can get a better understanding of the current structure from the surface to the bottom in the coastal waters of Portugal.

4. How do ADCPs using the Doppler principle work?

ADCPS utilize the theory of the Doppler effect: it emits an acoustic pulse through the column of water. Each time those pulses encounter a particle in moving water-such as sediment and small organisms-the frequency of reflected acoustic waves will change by means of the Doppler effect. One can now compute the velocity of water with respect to an ADCP just by knowing the shift in this frequency. Multiple transducers are fitted in the ADCPs, which have the ability to transmit and receive acoustic signals at various angles and hence measure the velocity components in many different directions. This enables horizontal and vertical components of the water flow to be obtained at different depths within the range of the instrument and thus provide a detailed profile of the coastal currents.

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

Several matters concerning equipment are critical in order to make good, high-quality measurements of coastal currents around Portugal. First of all, the materials used for constructing measuring devices must be of high quality and reliability; thus, resistant to seawater corrosion and also to mechanical tension developed by waves and currents.

This calls for equipment of smaller size and lighter weight to facilitate the deployment devices in various locations, whether on small boats, buoys, or in other applications. Also, a smaller and lighter device will reduce logistic problems occurring during its installation and recovery.

The other important factor is low power consumption, which would keep the equipment working for longer lengths of time with less frequent replacement of batteries or a big power supply source, especially when deployed in remote coastal areas.

Cost is also an important consideration. By lowering the cost, more devices could be used to measure and facilitate large-scale monitoring of the coastal currents. In this regard, the casing of ADCPs should be made from titanium alloy. The property of titanium alloy in corrosion resistance is very good, making it highly appropriate for marine conditions to endure long time exposure in sea water without decay. It features a high strength-to-weight ratio, meaning that one can achieve structural integrity without the total weight of the device being raised excessively.

6. Selection of equipment based on current measurement

Based on Usage

Shipboard ADCP: If the measurement has to be made while the ship is in motion, this will be appropriate. The water flow data can be continuously recorded while the ship moves around in different areas along the Portuguese coast and will be able to give a good understanding of the currents in a larger region.

Bottom-mounted ADCP: It is very appropriate for fixed-point measurements near the seabed. It will capture the flow characteristics close to the bottom quite accurately, which becomes very important in view of the interaction between the bottom topography and the currents. Buoy-mounted ADCP: For long-term monitoring, surface, and upper water column currents - the buoy-mounted ADCPs can be deployed in areas of interest within the coastal waters of Portugal and transmit data remotely.

Based on Frequency

• In shallow waters that are less than 70 meters deep, a general recommendation would often be a 600 kHz ADCP: because of the higher frequency it provides, while in shallower water, better resolution is offered and it can give a more developed current structure measurement.
• At less than 110-meter water depths, 300 kHz will be more relevant since it can support such frequencies well enough to get across correct velocity measures.
• For much deeper waters, say up to 1000 meters, a 75 kHz ADCP is recommended; its lower frequency can reach deeper and still capture reliable current data.

Some of the popular ADCP brands include Teledyne RDI, Nortek, and Sontek. However, a high-quality ADCP brand is the China Sonar ​PandaADCP. The whole instrument is made of titanium alloy material to ensure its durability and performance in the marine environment. Besides, it has an incredible cost-performance ratio. You can find more information about it on its official website: ​https://china-sonar.com/.

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