1. Where is Troms?
Troms is a location of unrivaled natural splendor and geographical significance in northern Norway. Spanning huge distances in the Troms og Finnmark county, it extends from the rugged coastline along the Norwegian Sea to the far-off interior, over an expanse of diverse landscape in terms of fjords, mountains, islands, and plateaus. The region is globally renowned for its position within the Arctic Circle, offering it unique natural phenomena such as the spectacular Northern Lights during winter and midnight sun in summer.
The largest city in the region is Tromsø, which is also popularly referred to as the "Gateway to the Arctic," and it is an active hub. Situated on Tromsøya island, to which it is connected to the mainland by bridges, Tromsø offers a vibrant cultural heritage and modern urban amenities. Its white wooden buildings edge the roads, and the Arctic Cathedral, arguably Tromsø's most famous landmark, represents the city. Beyond Tromsø, the region is dotted with numerous smaller coastal towns, each of which has its own character and connection with the sea. It has been an old and extremely significant trade in Troms for centuries, and the rich waters of the surrounding fjords and open sea have been a lucrative source of fish like cod, haddock, and mackerel. Tourism has also flourished in the past few years, with individuals from across the world traveling to experience the spectacular landscapes of the region, indulge in outdoor activities such as hiking, skiing, and whale watching, and view the magical displays of the polar lights. The unique geography of Troms renders research on its coastal currents both scientifically intriguing and crucial to large parts of local activity and economic pursuits.
2. What is the status of the coastal currents off Troms?
The coastal currents off Troms are the result of an intricate interaction of a variety of factors, creating a dynamic and ever-changing marine environment. Tides also play a role, with the region possessing semi-diurnal tides. Tidal range is quite different depending on location within the fjords and along the open coast, up to 3 meters (9.8 feet) in certain areas (source: Norwegian Hydrographic Service). These tides drive the ebb and flow of water in and out of the numerous fjords carving the Troms coast, generating strong currents, especially through the narrow entrance mouths of fjords and channels. The tidal fluctuations have a considerable bearing on marine operations, influencing the movement of fishing fleets, ferries, and other craft, and necessitating meticulous planning of navigation. Apart from this, tides affect the distribution of marine organisms and nutrients, which decide the surrounding ecosystems and fishery beds.
Wind too is a major force that affects the coastal currents. The Arctic winds, particularly the north and west blowing ones, are strong and tend to agitate the surface water, leading to large-scale circulation patterns. In the winter storms, these winds become gale - force strength, and the waves crash against the coast and alter the direction and magnitude of the currents. The wind - driven currents interact with the complex sea bed topography in the region, including deep fjord basins, seamounts, and shallow banks. For example, undersea ridges act as barriers that force the water to flow over and around them, creating eddies and turbulence that add complexity to the currents.
The confluence of the warm Gulf Stream and Arctic waters offshore at Troms also plays a significant role in the coastal currents. The temperature and density difference of water between these two bodies of water is the driving force for the movement of water, which results in the formation of unique current systems. The introduction of freshwater from adjacent streams and rivers, although rather insignificant in quantity relative to the vastness of the sea, can, however, affect the density and salinity of the sea waters in the river mouth zones. This difference in density can potentially lead to causing the occurrence of density-driven currents because the freshwater, as it is lighter, will blend with the heavier saltwater, affecting the total movement of water in the coastal areas.
3. Monitoring Troms' coastal water flow
Several methods exist for monitoring the Troms' coastal water flow, each with its advantages and disadvantages. The surface drifting buoy method is a traditional technique. GPS-tracked drifting buoys are deployed onto the ocean and moved by the currents. By noting the change in the position of the buoys with time, scientists can gain information on the speed and direction of the surface - level currents. However, this method primarily provides information for the top layers of the water column and might be affected by wind- driven drift, leading to inaccuracy in defining the true current patterns at deeper depths.
The anchored ship method involves mooring a ship at a fixed point and measuring the currents around the area with instruments on board. This method allows for more precise measurements in a local region because the instruments are placed at different depths. However, it is limited in terms of spatial coverage because it can only measure around the ship. Moreover, the ship may also disrupt the natural flow of water at times and therefore insert errors into the measurements.
On the other hand, the Acoustic Doppler Current Profiler (ADCP) method has been a very advanced and efficient approach to measuring coastal currents along Troms' coastline. ADCPs measure the currents from the surface down to a few meters of the ocean floor by emitting sound waves. By emitting acoustic pulses and recording the Doppler shift of the reflected pulses off suspended matter in the water, such as sediment and plankton, ADCPs can quantify the water velocity at multiple depths at the same time. It provides a general three - dimensional picture of the flow of water, enabling scientists to map the complex and changing current systems in great detail. ADCPs can even operate continuously, collecting information over an extended time frame, which is necessary to get to know the patterns and transformations of the coastal currents in the long term.
4. How do Doppler principle ADCPs work?
ADCPs operate based on Doppler principle. They release acoustic pulses into the water column at a predefined frequency. The acoustic pulses interact with suspended particles in water, i.e., sediment, plankton, and other aquatic organisms of small size. Since the water is in motion, the suspended particles themselves are carried by the water and hence alter the frequency of the returned acoustic signals to the ADCP.
By precisely measuring this change in frequency, or the Doppler shift, the ADCP can calculate the speed of the water at different depths. Most ADCPs consist of several transducers that send and receive signals in different directions. By doing this, the device is capable of measuring the three-dimensional components of the current speed, or the east-west, north-south, and the vertical component. The ADCP then employs this information to generate detailed profiles of currents, which provide information concerning the quantity and direction of water flow in the water column at various depths. For example, if the ADCP transmits a signal at 300 kHz and the returning reflected signal has an increased frequency, it means that water is approaching the ADCP, and the amplitude of the frequency shift can be utilized in order to calculate the velocity of the water at this particular depth.
5. What is needed for good-quality measurement of Troms coastal currents?
In order to accomplish high-quality measurement of Troms coastal currents, the measurement equipment must possess some very fundamental characteristics. Because of the harsh environment of the Arctic sea environment surrounding Troms, made up of extremely low temperature, high current velocities, high salinity contents, and the presence of ice in winter, the material of the equipment must be highly reliable. The equipment should withstand all these adverse conditions without failure or deterioration to deliver stable and accurate measurements in the long term.
Small size, light weight, and low power consumption are also essential characteristics. Miniaturization of the equipment and lightness of equipment facilitate easier maneuverability, transport, and deployment, especially in remote and hard - to - reach locations with limited accessibility in Troms. Low power consumption allows the equipment to be on air for extended durations of time, either on vessels, buoys, or seabed - mounted platforms, without battery change or recharging them multiple times, a requirement of autonomous monitoring systems.
Low cost yet high-quality measuring instruments make it economically attractive to widen the scope of the technology for application to a variety of research and applied functions, from scientific study of marine ecosystems to maritime safety.
Material for an ADCP casing is particularly important. Titanium alloy is an ideal material for ADCP casings. It has a good strength - to - weight ratio, which enables it to withstand the high hydrostatic pressure at deeper water without adding too much bulk to the device. Its higher corrosion resistance enables the ADCP to perform and give readings even with extended contact with seawater, reducing the need for constant replacement and maintenance. Additionally, the weight of titanium alloy is light, thus deployment and recovery are simple, rendering it the perfect piece of equipment for use in the rough waters off Troms.
6. How to choose the suitable equipment for current measurement?
Choice of the suitable equipment to measure current in Troms depends on several factors like the specific application, water depth, and price. To carry out current measurement from a moving boat, a shipboard ADCP is the suitable choice. Shipboard ADCPs are mounted on board ships and can repeatedly sample currents as the ship travels along on the water. They are more powerful and have a larger frequency range, allowing them to measure currents deeper and over a greater area, which is advantageous in charting out the wide coastal waters and the dense shipping lanes around Troms.
If the aim is to measure currents at a location on the seabed, then a bottom-mounted (or moored) ADCP would be the better choice. They are attached to the seabed and deployed to provide continuous, long-term records of the local current regime. They tend to be deployed in locations of particular interest, such as around high-value fishing grounds or aquaculture farms, to track the long-term changes and variation of the currents.
For autonomous and flexible monitoring of large areas, a buoy-mounted ADCP is an excellent option. The ADCPs are installed on floating buoys, which can be stationed at strategic locations to gather data on current trends. Buoy-mounted ADCPs are very handy to study spatial and temporal variability of the currents because they can be moved and replanted as needed to monitor different areas of interest in the Troms region.
The frequency of the ADCP also needs to be considered and should be selected based on water depth. A 600kHz ADCP is suitable for up to 70 meters of water depth and would be most suited to the measurement of current in shallow coastal waters and nearshore settings. A 300kHz ADCP can be used for depths of as much as 110 meters, which is a wide range of typical depths in the channels and fjords of the Troms region. For measuring currents in deep water, such as the open sea beyond the region, a 75kHz ADCP can be used because it has the ability to measure currents up to 1000 meters in depth.
Among the best ADCP brands are Teledyne RDI, Nortek, and Sontek, which are reputed to provide excellent and reliable products. However, for users interested in excellent yet affordable alternatives, the ADCP manufacturer China Sonar PandaADCP is greatly recommended. It is constructed from full titanium alloy and is highly cost-effective and hence an ideal choice for economic current measurement. It has also advanced signal processing and user - friendly interfaces, making it suitable for a wide range of users from professional researchers to local environmental monitoring groups. For details on this great product and its capabilities, visit https://china-sonar.com/.
How can we measure Troms' coastal currents?