How do we measure the San Diego coastal currents?

1. San Diego where?

San Diego, located at California's south-west tip, is an ocean-going city renowned for its pleasant weather, attractive beaches, and strong seafaring tradition. Curving around 70 miles of Pacific shore alongside a rich spectrum of beach and coastland shapes, there are sandy beaches, rocky shores.

The area was first occupied by the Kumeyaay tribe and left behind a glorious heritage. Spanish settlers also arrived during the 16th century and formed the first European-settlement of California. The initial presence is evident in the buildings of the city, most of them with Spanish - colonial style features. San Diego also has a number of army bases, which have contributed significantly to the growth and economy of the city.

San Diego Bay waters are part of the general Southern California Bight. The region comprises many bays, such as San Diego Bay, Mission Bay, and Coronado Bay. San Diego Bay in particular is a big natural harbor and a major port for commercial shipping, military use, and recreational boating. The sea floor morphology of the bay is complex with a mix of shallow coastal regions and deeper channels middle-bay. Addition of man-made infrastructures in the form of piers, breakwaters, and jetties has augmented only altering the local coast line.

2. What are the coastal currents off San Diego?

Coastal currents off San Diego are controlled by a mixture of natural as well as man - related factors. Tides play an important role as well. The region enjoys a semi-diurnal tidal regime, with two highs and two lows each day. During high tide, water rushes into the bays and creates powerful flood currents. But during low tide, water rushes out and generates ebb currents. The tidal currents are maximum in narrow channels and estuaries, such as the mouth of San Diego Bay.

The California Current, a cold north-flowing current, is a strong inshore influence. The current is a pipeline that delivers nutrient-enriched water from the north to feed a successful sea food web. Periods of upwelling, sometimes induced by northwest winds, carry cold, nutrient-rich water to the surface. These nutrients promote phytoplankton growth, the basis of the food web. In addition to the tides and the California Current, local topography, both onshore and offshore, affects the movement of currents. Seafloor canyons, for example, such as the La Jolla Canyon, deflect the deep-sea currents, and this influences the overall circulation in the region.

Man-made constructions also play a significant part in influencing the coastal currents. The massive port constructions in the San Diego Bay, like piers, breakwaters, and channels, change the natural flow pattern of currents. The constructions have the ability to produce local eddies, change the flow direction of water, and affect the sediment and nutrient transport.

3. How to observe the coastal water flow of San Diego?

Surface Drifting Buoy Method

One way to measure coastal water currents around San Diego is using surface drifting buoys. Surface drifters are fixed to the surface of the sea and permitted to move with the currents. They have GPS tracking equipment, which gives real-time positions. Scientists analyze the data for analysis of direction and velocity of surface currents. There are a few limitations of the method. Wind can easily misguide the buoys from the true current, leading to inaccurate readings of the subsurface flow. Additionally, free-drifting surface buoys expose data only of the surface layer of the water column and therefore provide only a partial perspective of the entire current structure.

Anchor Moored Ship Method

Anchor moored ship method refers to having a ship moored at one location. Scientists drop current meters off the side of the ship at different depths to measure the speed of the current. This method provides depth - specific information on the currents. It is, however, time - consuming and expensive as it entails having a research vessel anchored in place. The readings are also only representative of the region around the ship and hence it is challenging to get a complete picture of the coastal currents over a big area.

Acoustic Doppler Current Profiler (ADCP) Method

The Acoustic Doppler Current Profiler (ADCP) is a more sophisticated and convenient tool to measure coastal currents. ADCPs utilize the Doppler effect of sound waves to estimate water current speed at several depths. They emit pulses of sound into the water column. When pulses bounce off water particles, the frequency shift of the back-scattered pulses is utilized to calculate the water velocity. ADCPs can provide a total view of the current regime, from the surface to near the seafloor. Therefore, they are extremely well-suited to examine the complex coastal currents in the San Diego area.

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

ADCPs operate on the Doppler effect. They use piezoelectric transducers that emit sound waves into the water. When the sound waves encounter particles such as plankton, sediment, or bubbles in the water, some of the sound energy is reflected back to the ADCP. The time taken for the sound waves to travel to the particles and return provides an estimate of the particle distance.

The key to the measurement of current velocity lies in the Doppler shift. If the particles are swept along with the water current, the frequency of the backscattered sound waves received by the ADCP will be altered from the frequency of the transmitted waves. The magnitude of this change in frequency is directly proportional to the speed of the water along the acoustic signal path. To measure three-dimensional velocities, most ADCPs have at least three beams. Modern ADCPs also possess some sensors, like temperature sensors to compensate for the effect of water temperature on the speed of sound, compasses for orientation in determining the instrument direction, and pitch/roll sensors to deliver accurate measurements even under rough seas. The signals received are amplified, digitized, and processed to calculate the current velocity at different depths.

##. 5. What does equipment for high-quality measurement of San Diego coastal currents require?

In order to measure San Diego's coastal currents at high quality, the equipment should have a number of prerequisites. Material reliability is a must. The ADCP is to be run from a casing of material with high resistance to the destructive sea environment. Titanium alloy is optimal. It has excellent corrosion resistance, which is required for long-term deployment in seawater. Titanium alloy is also lightweight and strong and therefore more manageable and deployable. It has the strength that ensures the ADCP can sustain the mechanical stress of water flow and potential contact from debris.

Size, weight, and power consumption are also important. A small and light ADCP is more versatile because it can be mounted on a variety of platforms, including small research vessels, buoys, or underwater vehicles. Lower power consumption allows for longer - term deployments, especially when battery powered. Cost is another factor. A cheaper ADCP enables large - scale measurements, which enhance the spatial and temporal resolution of data collected.

6. The selection of right equipment for the measurement of current?

By Mounting Types

• Ship-mounted ADCP: Fitted on a moving vessel, this type of model is best suited for the large-scale mapping of coastal San Diego waters. When the ship is moving, the ADCP can continuously measure the currents and provide a large-scale impression of the current pattern.
• Bottom - mounted ADCP: Fixed on the seafloor, this type is best suited for fixed - point, long - term monitoring. It can be employed to provide useful information about the long - term trends and variability of the currents at a point.
• Buoy-mounted ADCP: Placed on a buoy, they are able to ride with the water, so it is possible to take measurements where fixed-point measurements are impossible. They are particularly handy in areas of high tidal currents or where a more mobile measurement platform is required.

Frequency Selection

The frequency of an ADCP depends on the depth of water. One 600kHz ADCP can be applied to up to 70m water depth. In the relatively shallow coastal waters along San Diego, one 600kHz ADCP can have excellent current profiles. A 300kHz ADCP is better suited to up to 110m water depth. It has greater range but still an appreciable level of accuracy. For the deeper waters in the outer parts of the Southern California Bight, a 75kHz ADCP is most suitable as it penetrates deeper into the water column.

There are several renowned ADCP manufacturers in the market, such as Teledyne RDI, Nortek, and Sontek. However, for those who want a cost - effective and good - quality option,the ADCP supplier China Sonar's PandaADCP is highly recommended. Made of all - titanium alloy, it is extremely tough in the marine environment. Having a very good cost - performance ratio, it is very appropriate to be used by researchers, coastal managers, and anybody who needs precise current measurement data. For more information, visit https://china-sonar.com/.

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