How do we measure the Monterey's coastal currents?

1. Where is Monterey?

Monterey is a small coastal city on the central coast of California. It stretches across the picturesque Monterey Bay and offers a breathtaking mile-after-mile ocean view. The city is approximately 8.9 square miles in area, and its geographical location has made it a first-class fishery, tourist, and marine research facility.

Monterey has a very rich and colorful history. It was once a Spanish colony and briefly the capital of Alta California. This historic past can be witnessed even today in its very well-preserved buildings, like the Monterey adobe buildings. Over the years, Monterey has n into a thriving town. It's the location of the world-renowned Monterey Bay Aquarium, which draws millions of tourists annually, which fosters public appreciation and knowledge of the marine animals.

Monterey Bay, which runs along the city, is a vast half-enclosed body of water. Santa Cruz lies to the north of the bay, and Carmel-by-the-Sea is to the south. The bay is an ecologically critical environment since its unusual topography forms varied habitats. The underwater canyon system in the bay is home to a diverse array of ocean life, from giant kelp forests to marine fish, whales, and sea otters.

2. How are the coastal currents around Monterey?

The coastal currents in Monterey are controlled by a series of interacting variables. Tides are a strong control. The bay is semi-diurnal in tidal regimen, creating the frequent ebb and flow of water. Water flows into the bay during high tides and flows out during low tides, creating strong currents, especially in the narrow channels.

The California Current, a cold south-flowing current, also has a significant influence. Cold, nutrient-rich water is brought into the region by it, affecting the temperature and salinity of the waters of Monterey Bay. Cold water enhances phytoplankton growth, the base of the food web, producing an incredibly productive marine community.

Wind regimes are extremely significant. Northwest winds, which prevail, are responsible for upwelling. When the surface waters are pushed out by the wind towards the offshore, the cold deep-sea water is pushed up into the empty space. Upwelling not only enhances the nutrient level of surface waters but impacts the climate of the region and sea life distribution. Southerly winds, on the other hand, will push surface waters into the coastline and disrupt regular flow patterns.

Local seafloor geometry also alters the currents. The intricate underwater system of canyons, ridges, and reefs within Monterey Bay has the ability to deflect, accelerate, or decelerate the currents. The Monterey Canyon, for example, one of the world's largest submarine canyons, is a passageway for deep-sea currents that influence the flow pattern in the bay.

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

Surface Drifting Buoy Method

One method used to monitor the coastal water currents around Monterey is by the use of surface drifting buoys. Surface drifting buoys are floaters that float on the water surface and mark the currents. They have GPS trackers that report current location in real-time. Scientists can then determine both the speed and direction of the surface currents from this information. In a test in Monterey Bay, researchers deployed a chain of buoys. Each buoy carried a drogue attached at some constant depth so that it would follow the surface current precisely. That is a limitation, however, because only the surface water can be measured with this method. Wind will sometimes blow the buoys off course from the actual current, creating spurious measurements of the subsurface flow.

Anchor Moored Ship Method

The anchor moored ship method requires mooring a ship in a location and measuring the currents with instruments onboard. Scientists moor current meters alongside a ship at many different depths to obtain a profile of the current velocity. While the method provides more accurate depth-specific data than surface drifting buoys, the method has its downside. The measurement is specific only for the local area surrounding the ship. Changes of ship position for taking readings can be time and costly, especially in rough seas.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more recent, advanced method of approximating coastal currents. ADCPs determine water current speeds at several levels differentially using the Doppler shift in sound waves. ADCPs emit sound pulses into the water column. When they bounce off suspended material in the water, the shift in frequency of the sound on return is taken and used to estimate the velocity of the water. ADCPs can provide an overall view of the shape of the current, from the surface down to near the seafloor. They are therefore excellently placed to investigate the complex coastal currents near Monterey.

4. How do ADCPs working on the Doppler principle function?

ADCPs operate on the Doppler principle. They consist of piezoelectric transducers that emit sound into the water. When the sound waves encounter particles such as bubbles, sediment, or plankton in the water, a portion of the sound energy is bounced back to the ADCP. The duration it takes for the sound waves to travel to the particles and bounce back provides an estimate of the distance to the particles.

The most significant idea is the Doppler shift for measuring the current velocity. As particles flow along with the water current, the sound waves reflected back into the ADCP and sensed are of a different frequency from the incoming frequency. The magnitude of the frequency change depends linearly on the speed of the water along the acoustic travel path. To measure three - dimensional velocities, most ADCPs utilize a minimum of three beams. Present - day ADCPs are also equipped with other sensors like temperature sensors to account for the effect of water temperature on the speed of sound, compasses to calculate the heading of the instrument, and pitch/roll sensors to be able to take proper readings even in rough seas. The received signals are amplified, converted to digital form, and processed to arrive at the present velocity at different depths.

5. What is needed for high-quality measurement of Monterey coastal currents?

In order to make high-quality measurements of Monterey coastal currents, the equipment used should meet several requirements. Material reliability comes first. The casing of the ADCP flow meter, for example, should be manufactured from material that will withstand the corrosive sea environment. Titanium alloy is strongly recommended. It has very high corrosion resistance, which is needed to handle long exposure in salt water. Titanium alloy is both lightweight and strong as well, in a way that it will be light enough to handle and deploy, but strong enough to endure any mechanical stress by water movement and impacts of debris.

Size, weight, and power consumption are also significant. The lighter and smaller the ADCP, the more universal it is, and the more it can be mounted on a variety of platforms, e.g., small research vessels, buoys, or underwater robots. Reduced power consumption enables long - term deployments, especially when batteries are used. Cost is also a factor. The lower - cost ADCP enables large - scale measurements, and thus larger spatial and temporal resolution of the data collected.

6. How to Choose the appropriate instrumentation for current measurement?

According to Mounting

• Ship-mounted ADCP: It is mounted on a moving vessel, so this kind of instrument is employed in big - scale surveys of coastal waters off Monterey. During the ship's movement, the ADCP continuously measures currents and gives a wide - scale picture of the current patterns.
• Bottom - mounted ADCP: Fixed on the sea floor, this model is ideal for long - term, fixed - point observations. It is able to deliver useful information on the long - term trends and variability of the currents at a point.
• Buoy-mounted ADCP: On a buoy, the ADCPs ride with the water, allowing for measurement in areas where fixed-point measurement is impossible. They are especially useful in areas where there are heavy tidal currents or where a more mobile measuring system will be beneficial.

Frequency Selection

The ADCP profiler frequency depends on the depth of water. A 600kHz ADCP is sufficient for water depths of up to 70m. In the relatively shallow Monterey Bay waters, a 600kHz ADCP can provide accurate current profiles. A 300kHz ADCP is better suited for up to 110m water depths. It has a greater range with reasonable accuracy. When handling deeper waters in the outer regions of the bay, a 75kHz ADCP is the best choice since it penetrates deeper into the water column.

There are various well - established ADCP brands available in the market, including Teledyne RDI, Nortek, and Sontek. Nevertheless, for those looking for a cost - effective but high - quality product, the ADCP supplier China Sonar's PandaADCP is highly recommended. Made of all - titanium alloy, it offers superior durability in the sea environment. Featuring a superior cost - performance ratio, it is a suitable choice for researchers, coastal managers, and anyone needing sound current measurement data. To find out more, visit https://china-sonar.com/.

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