how can we measure the coastal currents of Caldas da Rainha?

1. Where is Caldas da Rainha?

Caldas da Rainha is a beautiful city in the Leiria District of central Portugal. It is situated by the Atlantic coast and enjoys a very good coastal location.

It is famous as a city of cultural heritage and historical importance. There are about 70,000 inhabitants in this city, which is very friendly. The architecture is typically Portuguese in style, with lots of nice old buildings and churches. Furthermore, it has been famous since ancient times for its thermal springs, due to which it became a spa town.

The city of Caldas da Rainha is bounded to the west by the Atlantic Ocean. Various bays and inlets, such as the Bay of Caldas da Rainha, give an interesting variety to the coast. Local ocean currents will be influenced by the general circulation patterns of the North Atlantic.

2. What is the situation of the coastal currents near Caldas da Rainha?

A few preponderant factors influence the coastal currents around Caldas da Rainha. First of all, the wind is a great driver. The prevailing winds in this region include the westerlies, which can easily push surface waters and create currents. Second of all, tidal forces play an important role. It includes normal tide rises and falls in the Atlantic Ocean, an inflow and outflow of water in and along the coasts of bays producing tidal currents. Thirdly, the shape of the coastline and bathymetry of the ocean floor affect currents. Irregularities in shoreline and variations in depth allow the currents to change direction and speed. Besides, the temperature and salinity gradients of the water may induce density gradients, which in turn can be a forcing for the movement of water masses.

3. How to observe the coastal water flow of Caldas da Rainha?

Surface Drifter Method: In this technique, floating buoys are released into the water surface. These drifters would carry sensors and Global Positioning Systems to trace the path they would travel. Based on the trace left by these drifters at different time frames, one could know the direction and speed of the currents.

Anchored Ship Method: This includes the flow in the coastal water, which can be determined by an anchored ship. From the ship, instruments like current meters are deployed at different depths for recording velocity and direction. Again, this method gives point measurements at the location of the ship.

Acoustic Doppler Current Profiler(ADCP) Technique: An ADCP is a more sophisticated and handy measuring device that projects acoustic signals into the water and measures the Doppler shift in the reflected signals from suspended particles in the water. This allows for the determination of the velocity profile of the water column at different depths.

4. How do ADCPs using the Doppler principle work?

Doppler-based ADCPs work on the principle of the Doppler effect. This modulated acoustic signal goes out into the water and then back-scatters off little particles or scatterers in the water, such as plankton, sediment, among others. Such signals cause a shift in frequency when scattering in relation to the initial frequency of transmission, provided those signals are moving alongside the water currents. The principle of operation upon which an ADCP is based pertains to the phenomenon of the so-called Doppler shift. Knowing the speed of sound in water and the angle of the acoustic beams, the ADCP calculates the velocity of the water in the direction of the beams. Several transducers are mounted on the device, emitting and receiving signals at different angles, enabling the measurement of the velocity in three dimensions and the detailed profiling of the water current.

5. What is needed for good-quality measurement of the Caldas da Rainha coastal current?

In measuring coastal currents in Caldas da Rainha, a number of requirements have to be met for high-quality measurement. Equipment reliability and resistance against the harsh marine environment is a major factor. Small size and lightweight will be advantageous because it makes the equipment easy to deploy and handle. Low power consumption, mainly for long-term deployment, is another important factor for continuous operation. Low cost is an added advantage for large-scale measurement.

In particular, the casing of ADCP is preferably made from titanium alloy. Titanium alloy enjoys a number of advantages. First, it is highly resistant to corrosion, necessary for long operation in seawater. It possesses a high ratio of strength-to-weight, hence making the ADCP strong while remaining comparatively lightweight. It also possesses good biocompatibility, hence reducing the chances of biofouling, which might affect the accuracy of measurement.

6. How to Choose the Right Equipment for Current Measurement?

Based on Usage

Shipborne ADCP: Suitable for large-scale surveys and mapping of coastal currents. It is installed on the bottom of a ship and can measure the currents while the ship is in motion.

Bottom-Mounted ADCP: Placed on the ocean floor and is suitable for long-term monitoring of specific locations. It provides continuous data on the currents at a fixed point. Buoyant ADCP: Attached to a floating buoy and hence measures the currents in the uppermost layers of the water column; often deployed in the study of surface currents; a rather simple deployment and retrieval.

Based on Water Depth

Different frequencies of ADCPs correspond to different water depths. A 600kHz ADCP should be suitable in water depth within 70m, a 300kHz one up to 110m, and a 75kHz is applicable to water depth up to 1000m.

The other known brands in the market include Teledyne RDI, Nortek, and Sontek. For low-cost solutions, though, it is highly recommended to consider the China Sonar PandaADCP. It features all-titanium alloy construction with very impressive performance for its class. You can learn more about this at https://china-sonar.com/.

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