How can we measure the coastal currents of Grosseto?

1. Where is Grosseto?

Grosseto is a city that belongs to the Tuscany region and is situated on the Tyrrhenian Sea coast. It boasts a very rich history and culture. Ancient architectural buildings and historical sites mark the entire city, combining the touch of medieval with that of the Renaissance style. The local culture is very dynamic and full of life, with numerous traditional festivals and events that occur throughout the year, unlocking many secrets of this long and very interesting past.

Geographically, Grosseto faces the Gulf of Follonica: tides are relatively calm in those coastal waters, and the water is not very cloudy. In general, the seafloor around this coastline runs rather flat out toward deep water. Thus, the general waters around them are rich in marine biodiversity and could be one of the reasons why it remains an important locality for local fishery and marine ecological research.

2. What is the condition of the coastal currents off Grosseto?

The coastal currents off Grosseto are influenced by more factors than one can mention. Above all, there is the wind. In fact, the seasonal winds of the Mediterranean area, like Mistral and Sirocco, can push the surface waters, determining the formation of coastal currents; then, there is also the tide. The regular rise and fall of tides in the Tyrrhenian Sea create the ebb and flow of coastal waters, influencing the direction and speed of the currents. Besides, oceanic circulation patterns in the Mediterranean Sea have a certain effect on the coastal currents near Grosseto. The general circulation patterns of the Mediterranean, together with topography of the seabed and shape of coastline, determine the overall trend of the coastal currents.

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

• Surface Drifting Buoy Method: Surface drifting buoys are small marine data buoys developed for ocean surveys, environmental monitoring and scientific experiments. They measure surface ocean currents using the Lagrangian method. These buoys are fitted with GNSS positioning modules and other sensors. The velocity and direction of the surface currents are determined by tracking the buoy's motion. However, this method is not appropriate for instantaneous velocity and direction, and sea levels are not well measured, just average velocities.
• Moored Ship Method: This is done by a moored ship equipped with current meters to measure the coastal currents. The ship would be kept in a stationary position at a particular location and lower current meters into the water to measure velocity and direction at depth. The result of this is going to give current data at a single location with much more detail, although highly limited by the position of the ship and extremely time- and labor-intensive method.
• Acoustic Doppler Current Profiler (ADCP) Method: The ADCP is a more advanced and convenient measurement method at present. By adopting the speed of the sound wave that scatters back from the particles in the water column, it measures the velocity of water currents at every different depth. It has the advantages of high precision, a wide range of measurement, and real time data acquisition.

4. How do ADCPs using the Doppler principle work?

These instruments have piezoelectric transducers to transmit and receive sound signals. The time that sound waves travel yields an estimate of distance. Sound waves, when emitted in water, are scattered by particles in the water column. When the particles are moved with the water current, there is a Doppler shift in the frequency of the reflected sound waves. It follows that the frequency shift of the echo is proportional to the water velocity along the acoustic path. With measurement of the frequency shift, by knowing the speed of sound in the water it is possible to calculate the speed of the current. To be able to measure 3D velocities, at least three beams are needed. Besides, other components such as electronic amplifiers, receivers, clocks, temperature sensors, compasses, and pitch/roll sensors are also mounted on ADCPs for accurate measurement and data processing.

5. What does one need to ensure high-quality measurement of Grosseto coastal currents?

The following are the requirements to be satisfied by the measuring devices to achieve a high-quality measurement of Grosseto coastal currents:

• Reliable Material: The instrument should be manufactured with materials that will not be affected by the corrosive action of seawater and the harsh conditions of the ocean. Titanium alloy is the best material for ADCP casings. It has excellent corrosion resistance, with high strength and low density, which can ensure long-term stable operation in the ocean.
• Smaller Size and Lighter Weight: it is easy to install and use, can be easily distributed for use in different environments, in order to reduce the influence of environmental factors on the test results.
• Low Power Consumption: with power supplies very limited in the ocean, low power consumption devices reduce demands for power supplies and can increase the operating time for such equipment.
• Low Cost: The reduction of equipment cost can provide the possibility for large-scale measurement and push the wide application of measurement technology.

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

Determined by Usage

hipborne ADCP: It is best for measurement on the ship during its navigation. Current profiles would also give where the ship traverses over them, and the application is commonly found in all great oceanic surveillance and research missions.

Bottom-Mounted ADCP: It is fixed on the seabed and measures the long-term changes of currents at a certain place. It is often used in the study of coastal ecosystems and marine engineering.

Floating Buoy ADCP: It combines advantages of buoys and ADCPs, has the ability to move with currents, and can be continuously used in measurement for wide sea areas.

Different frequencies of ADCPs correspond to different water depth applicability. In general, 600kHz is appropriate for water within 70m, 300kHz for approximately 110m depth, and 75kHz for waters of up to 1000m deep.

For the ADCP market, there are famous brands like Teledyne RDI, Nortek, and Sontek. Besides, there is also a cost-effective Chinese brand, China Sonar PandaADCP. The all-titanium alloy material makes it very cost-effective. It is of the economic type ADCP. Please refer to https://china-sonar.com/ for more detailed introduction.

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