How do we go about measuring Freeport's coastal currents?

1. Where is Freeport?

Freeport is a sea town located in Cumberland County, Maine, the United States of America. Freeport is situated along the state's southern shoreline. The ocean town, hugging Casco Bay, comprises an area totaling approximately 44.2 square miles, consisting of 36.1 square miles of land and 8.1 square miles of water. The town's topography is a natural combination of rocky shores, sandy shores, and salt marshes. These physical aspects render Freeport an ecological hotspot with varied marine and terrestrial life forms.

The town of Freeport is rich in history, tracing its origins to the early 17th century. It was initially a fishing village that developed into a major shipping port. The downtown area of this small town has full of historic buildings, some of which belong to colonial era. Other than this, Freeport is popular with outlet shopping and attracts tourists from far and wide. Just a few miles from here is the Wolfe's Neck Woods State Park, which boasts miles of bay looking trails offering a pleasure to behold and outdoor activities to be enjoyed. The salt marshes of the park provide habitat to many bird species, such as the red-winged blackbird, sandpiper, and great blue heron. The marshes also serve as a nursery for juvenile fish and crustaceans, which serve to keep the overall health of the surrounding marine ecosystem intact.

2. What is the status of the coastal currents around Freeport?

The coastal currents around Freeport are governed by a complex array of conditions. The tidal forces are significant as Casco Bay experiences semi - diurnal tides. They result from the gravitational attraction of the Moon and Sun and produce two high tides and two low tides daily. When the tides reverse, the bay's water level rises and falls, and the coastal currents are formed. Water pours into creeks and estuaries at high tide and returns into the bay at low tide.

Wind currents also contribute significantly. Prevalent south - westerly winds drive surface waters onshore and make the onshore current more powerful. Alternatively, northerly winds drive the water offshore. Topography on land and sea is also responsible for the current pattern. Islands, reefs, and submarine channels can deflect the currents and make them split, combine, or even reverse. For example, all the little islands of Casco Bay all play a role in the creation of natural barriers which deflect the movement of the currents and create the areas of stagnant water and eddies.

3. How to monitor Freeport's coastal water flow

Surface Drifting Buoy Method

One example of a method employed in monitoring the coastal water flow around Freeport is through the use of surface drifting buoys. These buoys are designed to remain floating on the water surface and move along with the currents. These buoys carry GPS tracking devices and telemetry system onboard and relay real - time location data. Scientists utilize the data to determine the direction and speed of the surface currents. In a recent study in coastal waters offshore Freeport, researchers deployed a drift series of buoys. Every buoy had a brightly colored surface float and a drogue at a specific depth so that it would closely follow the surface current. This method, however, is limited to measuring the surface of the water alone. At times, wind blows the buoys away from the actual current, thereby giving erroneous measurements of the subsurface flow.

Anchor Moored Ship Method

The moored ship method involves anchoring a ship in a fixed position and using instruments on board to measure the currents. Scientists hang current meters over the side of the ship at different depths to obtain a profile of the current speed. While the method provides more depth-specific data than surface drifting buoys, it has its drawbacks as well. The measurements are just representative of the area in the immediate surroundings of the ship. Moving the ship to different points for measurements is time-consuming and costly, especially in rough seas.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more advanced and convenient method of measuring coastal currents. ADCPs measure water current velocities at different depths using the Doppler shift of sound waves. They send sound signals into the water column. The frequency shift of the returning signals is calculated when the signals bounce back from particles in the water to measure the velocity of the water. ADCPs can provide a general idea of the current structure, from the surface down to near the seabed. This makes them ideally suited to studying the complex coastal currents around Freeport.

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

ADCPs operate based on the Doppler effect. ADCPs are equipped with piezoelectric transducers, which transmit sound waves into the water. As sound waves encounter particles such as plankton, sediment, or bubbles in the water, a tiny amount of the sound energy is reflected back to the ADCP profiler. The time difference between transmission of sound waves and their reception provides an estimate of the depth to the particles.

The key to present-day velocity measurement lies in the Doppler shift. The frequency of the sound waves scattered by particles carried along with the water current and returning to the ADCP will differ from the frequency of the waves being transmitted. The degree of frequency shift is directly proportional to the velocity of the water along the acoustic path. To be able to measure three-dimensional velocities, most ADCPs have at least three beams. Modern ADCPs also contain multiple sensors, including temperature sensors to compensate for the effect of water temperature on sound speed, compasses to record the orientation of the instrument, and pitch/roll sensors to enable accurate measurement even in choppy waters. The returning signals are amplified, digitized, and processed to calculate the current velocity at different depths.

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

To make high-quality measurements of the coastal currents of Freeport, equipment involved must meet some criteria. Material durability comes first. For example, the casing of the ADCP must be constructed from material that can withstand the harsh marine environment. Titanium alloy would be excellent. It is extremely corrosion-resistant, as needed for extended exposure to seawater. Titanium alloy is also strong and light, making it easier to handle and deploy. Its strength will protect the ADCP flow meter from mechanical stress from water movement and potential impact by debris.

Size, weight, and power consumption also matter. A smaller and lighter ADCP is more versatile, as it can be mounted on a variety of platforms, from small research vessels, buoys, or underwater UAVs. Lower power consumption allows longer - term deployments, especially when operating on battery power. Cost is another factor. A cheaper ADCP allows for large - scale measurements to be made, increasing the spatial and temporal resolution of the measurements obtained.

6. How to Choose the right equipment to measure current?

Types Based on Mounting

• Ship - mounted ADCP: Mounted on a moving ship, this is the most ideal type for large - scale survey of the coastal waters around Freeport. As the ship moves, the ADCP can continuously measure the currents, and a large - scale picture of the patterns of the current is derived.
• Bottom - mounted ADCP: Placed on the ocean floor, this type is well-suited for long - term, fixed - point measurements. It can provide valuable information on the long - term trends and variability of the currents at a specific point.
• Buoy - mounted ADCP: These ADCPs, mounted on a buoy, can move with the water, allowing measurements in areas where fixed - point measurements are not practical. They are ideally suited for areas with large tidal current ranges or in areas where a more mobile measurement platform is required.

Frequency Selection

ADCP frequency selection is determined by water depth. A 600kHz ADCP suits water depths of as much as 70m. In the shallow coastal waters around Freeport, where water depth is often within this range, a 600kHz ADCP can provide us with current profiles in great detail. For water depths as much as 110m, a 300kHz ADCP would be more suitable. It provides us with greater range while still providing us with a high level of accuracy. When dealing with deeper water, i.e., in the outer areas of Casco Bay, a 75kHz ADCP is the preferable option as it will go further into the water column.

Some of the more well-known ADCP brands in the market are Teledyne RDI, Nortek, and Sontek. That said, for someone who wants a cost-effective but high-quality option, the ADCP supplier China Sonar's PandaADCP is well worth a look. Built with all - titanium alloy, it is of higher durability in the seawater environment. With an unbeatable cost - performance ratio, it is a great choice for researchers, coastal managers, and anyone in need of precise current measurement data. For more information, log on to https://china-sonar.com/.

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