How do we measure Yarmouth's coastal currents?

1. Where is Yarmouth?

Yarmouth, located on the southern coast of Maine in the United States, is a town renowned for its scenic coastal scenery. Bordering the Gulf of Maine, it is a county in Cumberland County, with a maritime history dating back centuries. Covering a total area of approximately 35.4 square miles, with 22.3 square miles of land and 13.1 square miles of water, Yarmouth has a unique geographical position.

The town is rich and eventful in terms of its history. It was initially a fishing village, which grew over time into a busy community. It is currently a hub for local and tourist - based economic pursuits. Yarmouth is renowned for its well preserved historic buildings, with the majority of the 19th - century buildings along its streets. The Casco Bay, which borders Yarmouth, also plays a major role in the town's scenery. The intricate network of inlets, islands, and coves of the bay fosters a diverse marine community with an abundance of wildlife, including seals, seabirds, and many species of fish. The economy of the town is also connected with the bay, as fishing, boating, and tourism are major contributors.

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

Coastal currents off Yarmouth are managed by a multi-dimensional interaction among various variables. Tidal forces, brought on by the Moon's and the Sun's gravity, are the major drivers. The Gulf of Maine experiences semi-diurnal tides, two highs and two lows daily. As the tides recede and come in, they also bring about tremendous changes in the direction and speed of the coastal currents. During high tide, water flows into the bays and estuaries around Yarmouth, while water retreats back to the sea during low tide.

Wind conditions also have a tremendous effect on the coastal currents. South - westerly prevailing winds tend to drive surface waters onshore, making the onshore current more intense. Conversely, northerly winds can push the water away from the coast. The local topography, including the shape of the coastline and also the underwater bathymetry, influences the currents. Islands, reefs, and undersea channels will deflect the currents to diverge, converge, or even reverse. For example, the numerous islands of Casco Bay can scatter the movement of the currents, causing pockets of dead water and eddies.

3. How to track the coastal water current of Yarmouth?

Surface Drifting Buoy Method

Monitoring the coastal water current of Yarmouth can be done through the use of surface drifting buoys. Surface drifting buoys are designed to drift on the water surface and ride the currents. They are equipped with GPS tracking devices and telemetry systems that provide real - time data on their location. Researchers can use this data to determine the direction and speed of the surface currents. For instance, in a recent study of the Yarmouth coastal waters, researchers deployed a string of buoys. Each buoy had a brightly colored surface float and a drogue at a particular depth to enable it to follow the surface current. But this method is only able to measure the surface layer of water. Wind can possibly cause buoys to drift away from the true current, and so measurements of subsurface flow would be inaccurate.

Anchor Moored Ship Method

The anchor moored ship method involves a ship being anchored at a fixed location and using instruments on board the ship to measure the currents. Scientists lower current meters down the ship's side at various depths to obtain a profile of the current's velocity. While this method provides more accurate depth-specific information than surface drifting buoys, it has its shortcomings. The readings are specific only to the immediate ship's vicinity. Transferring the ship to different locations for measurement is time - consuming and expensive, especially in seas with inclement weather.

Acoustic Doppler Current Profiler (ADCP) Method

Acoustic Doppler Current Profiler (ADCP) has also been found to be a more advanced and convenient method of measuring coastal currents. ADCPs employ the Doppler effect on sound waves to measure water current velocities at different depths. They project sound signals into the water column, and upon reflection off particles in the water, the frequency shift of the reflected signals is used to calculate the water velocity. ADCPs can provide a full description of the current structure, from the surface down to near the seabed. They are thus highly suitable to investigate the complex coastal currents off Yarmouth.

4. How do ADCPs based on the Doppler principle operate?

ADCPs operate on the Doppler principle. Piezoelectric transducers are installed in them which transmit sound waves into the water. When these sound waves encounter particles such as plankton, sediment, or bubbles of water, some of the sound energy is bounced back to the ADCP. The time duration for the sound waves to travel to the particles and back is an estimate of the distance to the particles.

The answer to the measurement of current velocity is the Doppler shift. When the particles are moving with the water current, the frequency of the backscattered sound waves detected by the ADCP profiler will be other than that of the transmitted waves. The magnitude of the frequency shift is proportional to the velocity of the water along the acoustic path. To measure three-dimensional velocities, most ADCPs use at least three beams. In addition, modern ADCPs are equipped with a variety of sensors, including temperature sensors to account for the effect of water temperature on the speed of sound, compasses to determine the instrument heading, and pitch/roll sensors to offer reliable measurements in spite of disturbed seas. Received signals are amplified, digitized, and processed to calculate the current velocity at different depths.

5. What are the requirements for high-quality measurement of Yarmouth coastal currents?

In order to provide high-quality measurement of Yarmouth's coastal currents, the equipment used must meet some conditions. Material reliability is essential. The ADCP casing, for example, must be made of a material that is strong enough to withstand the corrosive sea environment. Titanium alloy is an ideal choice. It has outstanding corrosion resistance, which is essential for long-term operation in seawater. Titanium alloy is also strong and light, and therefore easy to handle and deploy. Its strength ensures that the ADCP will resist the mechanical forces of water currents and potential impacts from objects.

Size, weight, and power usage are also important. A lighter and smaller ADCP current meter is more versatile, as it can be used on a variety of different platforms, like small research vessels, buoys, or even remotely operated underwater vehicles. Lower power usage allows longer - term deployments, especially where batteries are used for power. Cost is also an issue. A lower - cost ADCP makes large - scale measurements possible, scaling the spatial and temporal resolution of the data collected.

6. What is the suitable equipment for measuring current?

Types Based on Mounting

• Ship-mounted ADCP: It is mounted on a ship traveling along. It is most suitable in conducting large-scale surveys of sea waters around Yarmouth. As the ship travels, the ADCP will be in a position to measure the currents at all times, and this will provide a broad-scale view of the current flow.
• Bottom - mounted ADCP: Mounted on the sea floor, this type is suitable for long - term, fixed - point observations. It may be helpful in providing valuable information about the long - term trends and variability of the currents at a specific site.
• Buoy - mounted ADCP: These are installed on a buoy and can track the water, taking measurements where fixed - point measurements are not possible. They are particularly useful in areas of high tidal currents or where a more mobile platform for measurement is required.

Frequency Selection

The frequency of the ADCP depends on the depth of water.

• A 600kHz ADCP can be utilized in water depth of up to 70m. In Yarmouth's shallow coastal waters where the depth is typically within this limit, a 600kHz ADCP can provide complete current profiles.
• A 300kHz ADCP would be utilized in water depths up to 110m. It has greater range and is still of acceptable accuracy.
• For the deeper waters, such as those of the outer parts of Casco Bay, a 75kHz ADCP would be the best option, as it can penetrate into the water column more deeply.

There are several well - known brands of ADCPs in the market, such as Teledyne RDI, Nortek, and Sontek. But in the case of somebody who wants to make an economical yet high - quality purchase, the ADCP supplier China Sonar's PandaADCP is suggested. Made of all - titanium alloy, it provides superior durability under marine conditions. With a superior cost - performance ratio, it is the perfect option for researchers, coastal managers, and anyone who requires stable current measurement data. To learn more, visit https://china-sonar.com/.

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