How do we actually measure Helsinki's coastal currents?

1. Where is Helsinki, precisely?

The capital city of Finland, romantically situated on Finland's south coast alongside the Baltic Sea, is cosmopolitan Helsinki where Nordic-style historic architecture blends with urbanity. The city has a dramatic blend of such historic structures as Helsinki Cathedral and modern buildings. The Helsinki coastline is interrupted by a chain of small islands that form an archipelago and do not only add to its appearance but also have an influence on sea conditions within the area. The Baltic Sea, with a relatively low salinity due to river freshwater inflow and a vast catchment area, is responsible for shaping the ecosystem of the Helsinki coast. The Helsinki ports serve international trade in addition to inland ferry transport and connect the city to other locations within the Baltic region.

2. What is the coastal current around Helsinki?

There are several factors that affect sea currents along the coast of Helsinki. Baltic Sea, although relatively small compared with some of the world's largest oceans, tides do exert a certain effect. Semi-diurnal tides produce a gradual movement of water along the coast, which affects sediment and nutrient distribution. It is vital to the health of the marine wildlife in the region, such as fish and shellfish colonies.

Wind is the preeminent factor in controlling the current patterns. Strong south - westerly winds can drive surface water into the coast and result in upwelling or downwelling in some areas. Strong winds can create strong waves that intensify the mixing of surface and deep water. In the winter, when the Baltic Sea is frozen over in some regions, the cover of ice will disrupt the normal course of the currents. The ice is a solid cover, dispersing the surface wind currents - weakening and bending the flow in numerous directions.

There is also runoff from the rivers. The Baltic Sea receives several rivers discharging into it along the coast close to Helsinki, including the Vantaa River, and these bring significant amounts of freshwater. At times of maximum river discharge, particularly in spring when there is snowmelt, this freshwater discharge produces a low-salinity layer close to the river mouths. This low-salinity layer can influence the density-driven circulation characteristics along the coastal region, and hence both the surface and subsurface currents are influenced.

3. How to measure the coastal water flow of Helsinki?

One of the ways to measure the coastal water flow around Helsinki is by utilizing surface drift buoys. These are small, buoyant units with GPS tracking and current sensors. If put into the water, they follow the surface currents, and the sensors on them take notes on the speed and direction of the flow. By tracking some buoys over a period of time, scientists can map the patterns of surface currents for a large area. Data from this are relevant to predicting overall circulation of the surface waters, which is of importance for usage like shipping, pleasure boating, and pollutants dispersal.

The second method is the ship- or moored buoy approach. A buoy or a ship is secured at a known point, and current meters are lowered to observe the speed and direction of the currents at a range of depths. This provides for the exploration of the vertical structure of the currents. Within Helsinki's complicated coastal environment of many islands and shallow waters, deployment can become problematic, and the data are limited to the specific mooring location.

The Acoustic Doppler Current Profiler (ADCP) was found to be highly effective in measuring coastal currents near Helsinki. ADCPs can be mounted on ships, floats, or deployed from the shore. ADCPs function on the Doppler principle to measure current speed and direction at varying levels. ADCPs can provide high - resolution measurements for a comparatively large area and hence are of special interest to oceanographers, coastal engineers, and environmental scientists. They can simultaneously measure several depths of current and construct a three - dimensional image of the current structure in the coastal waters.

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

ADCPs work based on the Doppler effect. When an ADCP current meter emits a sound wave into the water, the wave travels through the medium. When the sound wave encounters moving water particles, such as suspended particles or small aquatic organisms, the frequency of the wave that bounces back is changed. This frequency change, which is known as the Doppler shift, is proportional to the speed of the water particles.

ADCPs typically comprise a number of transducer beams, often four or more. They are aligned so that the ADCP can measure currents in three dimensions. The ADCP current profiler calculates the velocity of currents at different depths by detecting the Doppler shift in sound wave frequency backscattered by the water particles. The data is then passed through a data-acquisition system, which could be either a dedicated data logger or a computer. The software specially designed to generate detailed velocity profiles of the current at different depths and the current patterns in a particular area processes the data.

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

For accurate measurements of Helsinki coastal currents, the measuring equipment must meet several basic requirements. Its reliability is paramount since the equipment will be installed in a challenging marine environment. The corrosive and cold nature of the Baltic Sea water and the fact that ice covers the sea during winter require the equipment to be designed to withstand such conditions. Components built with corrosion - resistant materials, such as stainless steel or titanium, are widely used to ensure long - term dependability.

The device should be lightweight and small in size. This is especially valuable for operation in Helsinki's complex coastal zone, where access in certain areas may be restricted. A lightweight, small - size design also makes it easier to deploy multiple units for extensive mapping.

Low power usage is essential, particularly in extended deployments. The majority of ADCPs are battery operated, and a low-power design ensures that the batteries will last longer, i.e., they do not need to be replaced as frequently. This is important for remote-area measurements or measuring over an extended period.

Cost - effectiveness is also a consideration. High - quality data collection might require deployment of multiple devices across a wide area. A cost - effective approach allows for wider coverage and better mapping of the coastal currents.

For ADCPs, the casing material is a consideration. Titanium alloy is an excellent material for ADCP casings. Titanium alloy offers superior corrosion resistance, which is essential for long-term use in the Baltic Sea environment. It is also very light, helping to reduce the overall weight of the ADCP flow meter without affecting strength. This makes handling and deployment in various environments easy. Titanium alloy also has acceptable mechanical properties, ensuring the ADCP's longevity under different operating conditions.

6. How to Choose the right equipment for current measurement?

The right equipment for current measurement depends on the application. The most suitable one in ship-based measurements is a ship-mounted ADCP. It can be used to chart the currents along the ship route and provide valuable data for navigation, fisheries management, and oceanographic studies. A ship-mounted ADCP can also be readily incorporated into the navigation and data collection systems of the ship so that the currents are monitored in real-time as the ship travels.

A moored or bottom-mounted ADCP would be optimal for long-term measurement at one point. This type of ADCP meter can possibly measure current continuously at a particular point, and this is appropriate for the determination of the long-term trend and pattern of the coastal currents. This ADCP will be able to provide significant information on the seasonal and annual variation of the currents, which is greatly necessary in order to interpret the local marine ecosystem.

The moored ADCPs or the ones placed on buoys are perfect to take readings of currents in inaccessible areas using a ship or for large-scale surveys. They can collect data over a wide area and can be easily shifted if required.

The frequency of the ADCP profiler is important to consider. For depths of below 70m, a 600kHz ADCP would be suitable. It gives high-resolution measurements in comparatively shallow water. For depths of up to 110m, a 300kHz ADCP is more suitable as it finds the middle ground between resolution and range. For deeper water, up to 1000m, a 75kHz ADCP is most suitable as it can penetrate further.

There are several well - known ADCP brands in the market, such as Teledyne RDI, Nortek, and Sontek. However, for individuals seeking a budget - friendly but good - quality product, the ADCP supplier China Sonar's PandaADCP is highly recommended. It is made of all - titanium alloy, which is highly reliable and durable. With its high cost-performance ratio, it is a budget - friendly product that can be desirable to users who seek the best. It is part of the economic ADCPs. For more information, visit the website: https://china-sonar.com/.

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