How to measure coastal currents of Montpellier?

1. Where is Montpellier?

Montpellier is a vibrant, yet refined city, located in the department of Hérault, region of Occitanie in southern France. It stands very well placed as a coastal city facing the Mediterranean Sea and therefore enjoys a variety of rich natural beauty and strong maritime traditions.

The city is globally known for its warm and sunny weather; the city experiences a scorching long summer, whereas winters remain moderate. That is very alluring in terms of tourist attraction as well as settling down in town. Montpellier is steeped in history and thus acts as the juncture of cultures. As such, one may locate a lot of historical monuments, museums, art galleries, and rowdy street markets representing the glorious past and present.

Further east from Montpellier lies the Gulf of Lion, well-renowned and part of the Mediterranean Sea. The water around Montpellier is shallow towards the coast, gradually sloping towards deeper levels if one goes inside the sea further. There is crystal-clear water, blue in color, and rich in every type of marine life, making this place a real paradise for the divers and marine lovers.

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

The coastal currents near Montpellier are influenced by several factors. First, the prevailing winds in the region play a crucial role. The Mistral, a strong northerly wind that blows frequently in the area, can significantly affect the surface currents, pushing the water along and creating complex flow patterns.

Another important factor which is unique in this region, is tide: of course, tidal ranges within the Mediterranean Sea are relatively small when compared with other seas, yet tides still account for an ebbing and a flowing which is added to the general flow of the coastal currents.

Another factor is the topography of the seafloor. Irregularities and slopes of the seabed next to Montpellier can let the currents be deflected and changed in direction, with local eddies and areas with speedups or slowdowns. The presence of rivers running into the sea in proximity, like the Hérault River, may also influence coastal currents with additions of fresh water and changes in its density and flow.

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

Surface Drifting Buoy Method: In general, surface drifting buoys are used very much to trace the movement of ocean surface currents. GPS or other tracking devices fitted into buoys, set free in the water, simply drift with the currents and report continuously on the position to present data over the direction and speed of surface currents.

Moored Ship Method: An anchored ship deploys an array of instruments to include the current meters, which determine the flow at various depths of water. In doing this, these meters are being suspended below the ship, where they can stay for a longer period of time so that scientists can gather information on both velocity and direction of the currents at upper and lower levels.

Acoustic Doppler Current Profiler(ADCP) Method: Now, an advanced and more convenient measurement technique is ADCP. It has increased significantly in recent years because it is one of the most accurate techniques for measuring currents and simultaneously at different levels of depth.

4. Principles of ADCPs Working

The working principle of ADCPs is based on the Doppler principle. They transmit acoustic signals into the water. If these signals collide with moving particles in the water, such as suspended sediments or plankton, because of the Doppler effect, the frequency of the reflected signals is changed. This shift in frequency is measured by the ADCP and, from it, calculates the velocity of the water in which the particles are moving.

Thus, it will be able to create a profile of the current velocities at different levels within the water column by sending and receiving signals with variations in angles and depths that enable an appropriate determination of the precise vertical structure of the coastal currents.

5. What is required for high-quality measurement of Montpellier coastal currents?

From an equipment point of view, several aspects should be considered for high-quality measurement of coastal currents in Montpellier.

Material Reliability: Materials used in the equipment must be highly reliable, especially within the harsh marine environment. The casing of the ADCP is preferably to be made from a Titanium alloy. Corrosion resistance is very essential for long use in seawater, which titanium alloy material features. It also withstands high pressures at greater depths without deforming or losing its integrity.

Size, Weight and Power Consumption: The equipment must be compact in size and lightweight for the easy mobility of deployment and operation. The power consumption must also be very low, especially for devices intended to work for considerable lengths of time at sea, because of the low frequency of battery replacement or recharging.

Cost: It must be in such a reasonable cost to facilitate its equipment in large scales of measurement, so that one can cover most of the areas along the coast for more accurate coverage of data representation.

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

Determined by Usage:

Shipborne ADCP: convenient for current measurement during a ship survey. It can be installed on the ship's hull, which is advantageous when currents in relatively wide areas are measured in the moving ship.

Bottom-mounted ADCP: These are ideal for long-term current monitoring at a fixed position. The ADCPs are deployed on the ocean floor and record current data continuously at one point.

Floats ADCP: These are being used considerably in tracking surface currents and hence can become very important assets in acquiring information on the upper-layer movement of the ocean.

Frequency

600kHz ADCPs operate best for water within the depth of 70m, allowing for high-resolution measurements in relatively shallow waters.

300kHz ADCPs shall be appropriate to use in waters to a depth of up to 110m as they allow a good resolution-depth-of-penetration balance.

75kHz ADCPs operate in deeper waters and can work to a depth of 1000m.

Some of the well-known brands where ADCPs are sold include Teledyne RDI, Nortek, and Sontek. However, if cost-effective options are being researched upon, then China Sonar ​PandaADCP is highly recommended. Made of all-titanium alloy, the instrument has incredible cost performance and belongs to the economic type of ADCP. You can find more on their website: ​https://china-sonar.com/.

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