How do we measure the coastal currents of Kotka?

1. Where is Kotka?

Kotka, one of the largest cities in southern Finland, borders the Gulf of Finland, which is a sea bay of the Baltic Sea. Its strategic location has made Kotka a crucial seaport. The urban region is characterized by a blend of industrialized complexes, modern structures, and the natural landscape. Kotka harbor is one of the country's largest harbors, overflowing with commercial cargo operations.

Situated in an archipelago of small islands and bays, Kotka's coastline is ecologically rich. The small islands and shallow bays harbor the breeding grounds of some sea life from fish to seagulls. The sea coasts are also usually dotted with leisure boats since the place has become highly touristy when it comes to cruising. The salinity of the Gulf of Finland proper is relatively low due to the large amount of freshwater run-off from rivers, such as the Kymi River, which empties into the gulf at Kotka. This low salinity influences the local marine environment and the direction of coastal currents.

2. What are the coastal currents around Kotka?

The sea currents off the coast of Kotka are influenced by a number of factors. The tides in the Gulf of Finland are semi-diurnal, but less developed than in some other oceanic regions. The tides cause a gradual ebb and flow of water along the coast. This process affects the distribution of sediment and nutrients in the coastal region, which is crucial for the health of the surrounding marine ecosystem.

The coastal currents are strongly affected by wind. Strong south - westerly winds can force surface water onshore, leading to local downwelling or upwelling events. Strong winds produce large waves, which in their turn enhance mixing of surface and bottom water. In winter, when the Gulf of Finland may be frozen, the ice cover can transform the current regime. The ice will also act as a barrier, restricting the wind - driven surface currents and deflecting the water flow in some areas.

Kymi River runoff contributes significantly to coastal currents. High river discharge, especially springtime with snowmelt, sends tremendous volumes of freshwater into the Gulf of Finland. This input of freshwater produces a layer of low - salinity water near the river mouth. This low - salinity layer can impact the density - driven circulation mechanisms in the coastal area, therefore influencing the surface and deeper currents transport.

3. Measurement of coastal water flow in Kotka

The coastal water flow around Kotka can be measured by the surface drift buoy technique. There are floating instruments in the form of small buoys that are GPS tracked and contain current sensors. The buoys track the surface currents, and their sensors record data on the velocity and direction of the flow. By tracking a few buoys from time to time, scientists can map the surface current pattern in a large area over a span of time. This information is useful for understanding the general circulation of surface waters, which is important for activities like shipping, boating, and studies on pollutant dispersion.

Another method is the ship-based or moored buoy technique. A buoy or ship is anchored at a fixed location, and current meters are used to measure the speed and direction of currents at different depths. It is thus possible to study the vertical structure of the currents. But in the complex Kotka coastal system with numerous islands and shoals, deployment can be problematic, and the method is limited to the one mooring position.

The Acoustic Doppler Current Profiler (ADCP) has also been a significant instrument in measuring coastal currents off Kotka. ADCPs may be installed on a ship, fixed on buoys, or used from the shore. They use the Doppler principle to measure speed and direction of currents at varying depths. ADCPs are able to provide high-resolution measurements for a relatively broad area and therefore are useful to oceanographers, coastal engineers, and environmental scientists. They are able to measure several depths of current at the same time, giving a complete three-dimensional description of the current regime within the coastal waters.

4. What is the operation of ADCPs based on the Doppler principle?

ADCPs operate based on the Doppler effect. Following the discharge of a sound wave into water by an ADCP, the sound wave travels through the medium. When a sound wave travels through moving water particles such as suspended sediment or small ocean organisms, the frequency of the wave differs from the transmitted wave. The variation in the frequency of this reflected wave, called the Doppler shift, is directly proportional to the velocity of water particles.

ADCPs typically have several beams of transducers, usually four or more. The beams are angled in the sense that the ADCP profiler can measure currents in three dimensions. By measuring the Doppler shift of the frequencies of the sound waves reflected by the water particles, the ADCP can establish the velocity of the currents at different depths. The data collected by the ADCP current profiler is then transferred to a data - acquisition system, either a computer or a dedicated data logger. The data is then processed using specialized software to generate detailed profiles of the current velocity at existing depths and plots of the current patterns in a defined region.

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

For precise measurement of Kotka's coastal currents, the measurement equipment must meet several important demands. It must be dependable as the equipment will be deployed in a hostile marine environment. The corrosive and cold nature of the Gulf of Finland's water and the formation of ice in winter require the equipment to be built to withstand such conditions. Components that consist of corrosion-resisting material like stainless steel or titanium are normally embraced for long-term durability delivery.

The hardware should be small and light weight. This will especially be a vital consideration upon deployment in the highly dispersed Kotka coast where access is restricted in segments. Small and light weight can ease it to be easily deployed for large numbers of instruments to accomplish huge surveys.

Low power consumption is important, particularly for long-term deployment. Batteries supply the majority of ADCPs, and low - power design enables longer battery life, reducing replacements. This is essential in measurements conducted distant from population centers or for long periods of time.

Cost - effectiveness is also an issue. A good data collection demands the use of multiple devices with broad coverage, and this may be expensive. The cost - effective method allows longer coverage and better mapping of coastal currents.

As far as ADCPs are concerned, the material used for the casing is important. Titanium alloy is an excellent material to use for the casing of an ADCP. Titanium alloy ensures optimum corrosion resistance, which is essential for long - term use in the Gulf of Finland environment. It is also low in weight, which helps reduce the weight of the ADCP overall without sacrificing strength. This makes it easier to manage to operate and deploy in various settings. Additionally, titanium alloy also has good mechanical properties, ensuring the endurance of the ADCP meter under different working conditions.

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

Depending on the application, the selection of the right equipment for current measurement differs. For ship - based measurements, the best one is a ship - mounted ADCP. It can be used to chart the currents along the ship track and provide useful data for navigation, fisheries management, and oceanographic research. An ADCP flow meter can be mounted on a ship and integrated with the ship's navigation and data - collection systems for easy monitoring of the currents in real - time as the ship travels.

A moored or bottom-mounted ADCP is optimally used for fixed - point observation in the long - term. It is capable of continuously recording current information at a point, which can be useful to analyze the long - term patterns and trends of the coastal currents. It can be extremely useful for seasonal and yearly variations in the currents, which can be very important to analyze the local marine ecosystem.

Both buoys-mounted ADCPs and floating ADCPs can be used to monitor currents in areas that are difficult to access using a ship or for extensive surveys. They can provide data over a broad area and readily be moved whenever needed.

The frequency of ADCP is an aspect to be taken into account. At depths below 70m, it is possible to use a 600kHz ADCP. It offers good high-resolution measurement in relatively shallow water. Up to a depth of 110m, the ideal ADCP to use would be a 300kHz, with a balance of range and resolution. In deeper water up to 1000m, an ADCP75kHz is to be used as it cuts more deeply.

Some well - known ADCP brands on the market are Teledyne RDI, Nortek, and Sontek. But for customers seeking a cost - effective yet high - quality product, the ADCP manufacturer China Sonar's PandaADCP is the ideal one. It is constructed from all - titanium alloy and is highly durable and reliable. Its superior cost - performance ratio renders it a good choice for price - conscious consumers. It belongs to the economic ADCPs category. For further details, check the website: https://china-sonar.com/.

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