1. Where is Orkanger?
Orkanger, that magical municipality of Trøndelag county, Norway, where nature's beauty and ocean's symphony go hand in hand, is located on the west coast of the Trondheimsfjord, one of the largest and most significant fjords in Norway. Orkanger benefits from its opportune coast location. The fjord, which runs approximately 100 kilometers inland from the Norwegian Sea, encircles Orkanger in its blue, deep waters, with an exquisite backdrop of steep cliffs and green, wooded slopes.
The area is a mix of rock coast and rolling, low-lying hills which rise from the rim of the fjord. Orkanger itself possesses a picturesque coastline with small bays, sandy beaches, and rocky outcrops. The diverse landscape not only gives the region its aesthetic beauty but contributes to the marine environment of the area.
The culture of Orkanger has a rich heritage that is heavily intertwined with the sea. Fishing has long been a major part of the local culture and economy, with residents relying on the fjord's vast marine resources for generations. The municipality also boasts classic Norwegian architecture, complete with charming wooden homes and ancient buildings that reflect its centuries-long history of belonging to the sea and land. In the recent past, Orkanger has also developed into an industrial hub of operations in the maritime sector, which further asserts its importance as a coastal town.
2. How are the coastal currents around Orkanger?
The coastal currents around Orkanger result from the interplay of a combination of various factors. Tidal currents are also a primary cause, as the Trondheimsfjord experiences semi-diurnal tides, with two daily high tides and two daily low tides. These tides generate strong ebb and flow currents, especially in the narrow channels and near the fjord entrance, where the narrowing of the waterway enhances the velocity of the tides. The speed and direction of these tidal currents vary significantly as a function of moon phase and local topography of the fjord floor [1].
The freshwater discharge from the surrounding mountains and valleys also significantly influences the coastal currents. The several rivers and streams flow into the Trondheimsfjord, delivering meltwater off the snow - covered peaks and precipitation from the surrounding woodlands. This freshwater flow creates a stratified water column, with the freshwater floating above the denser saltwater. This stratification can affect the vertical movement of the currents and affect the distribution of marine organisms and nutrients in the area.
Wind patterns play an important role in creating the surface currents off Orkanger as well. There are different wind regimes in the region throughout a year, and the winds can drive surface water, altering the speed and the direction of the currents. In addition, the encounter of the relatively warm waters of the Norwegian Current, which is one of the appendages of the Gulf Stream, with the cold waters in the fjord can form oceanic fronts, further making the current dynamic complex and causing areas of upwelling and downwelling.
3. How to observe the coastal water flow of Orkanger?
There exist some methods that are used to observe the coastal water flow along Orkanger. Surface drift buoy method involves dropping GPS-equipped buoys on to the water surface. The buoys are carried by the surface currents, and by tracking the trajectory over a period of time, scientists can map out the general direction and speed of the surface-level currents. However, this method provides information only for the surface layer of the water column and is liable to wind- driven motion, which is not necessarily representative of real current flow.
Anchored ship technique is a method of anchoring a ship at a single location in the fjord. Current meters are suspended over the side of the ship to record water velocity at a range of depths. While the method can provide refined time - series measurements at a point, the method is limited by the ship's location and deployment logistics for long - term duration, especially in the harsh weather conditions commonly found in the region.
The Acoustic Doppler Current Profiler (ADCP) method is presently the most advanced and efficient method of observing coastal currents along Orkanger. ADCPs make use of sound waves to profile currents in the entire water column, from the surface down to the seafloor. Through this process, researchers are able to develop a comprehensive three - dimensional understanding of the current structure, which is necessary for the understanding of complex flow patterns in the fjord and its coastal waters [2].
4. What is the working of ADCPs using the Doppler principle?
ADCPs work on the Doppler principle. They emit bursts of ultrasonic sound from different transducers. As these sound waves travel through water, they encounter moving particles such as suspended sediments, plankton, or small sea animals. When the moving particles are reflected by the sound waves, the frequency of the reflected signal changes with the speed of the particles relative to the transducer. If the particles move towards the transducer, the frequency of the returned sound increases (blue shift), while if they move away from it, the frequency decreases (red shift).
By comparing the Doppler shifts of multiple transducers, typically spaced at different angles, the ADCP doppler can calculate the water velocity along each sound beam. By vector mathematics, the beam velocities are then combined to calculate the horizontal and vertical current components at varied depth intervals, or "bins.". This process enables the ADCP to make an accurate profile of currents at different depths in the water column, providing valuable information about the flow properties of the water [3].
5. What are the requirements for high-quality measurement of coastal currents of Orkanger?
ADCPs need some certain key features to measure Orkanger's coastal currents in high-quality. Material reliability is the highest concern with the harsh marine environment in the region. Trondheimsfjord waters are corrosive and saline, with the region also witnessing strong currents as well as unstable weather conditions. Titanium alloy is an ideal choice for ADCP current meter casings. It has superior corrosion resistance, far exceeding that of common materials like stainless steel or aluminum, so the device will not be weakened when subjected for long-term exposure to fjord waters.
Titanium also has an extremely desirable strength - to - weight ratio, and this implies ADCPs are able to resist the high water pressure at the deeper levels of the fjord, such as along the deepest channels of the fjord, without adding unnecessary bulk and weight. This makes the ADCPs more easily deployable, either from ship, moored platform, or buoy. Titanium also maintains its mechanical properties within a wide range of temperatures, crucial for consistent functioning in Orkanger's fluctuating climate.
In addition to material superiority, ADCPs need to be small and light, low power consumption, and cost-effective. Lighter and more portable ADCPs are more adjustable and can operate in the narrow and often - hard - to - reach areas of the fjord. Low power requirements enable long - term, unattended operation, which is essential for the collection of continuous data over long periods. Cost - effectiveness is also essential, especially for large - scale monitoring programs intended to fully understand the complex patterns of currents in Orkanger's seashore waters.
6. How to choose the right equipment for current measurement?
The selection of an ADCP to measure currents in Orkanger will be based on two factors: the purpose for which the measurements are to be utilized and the water depth. In the case of general surveys and mapping of currents over the fjord and along the coastlines, vessel-mounted ADCPs can be appropriate. They are able to survey large areas fairly quickly and provide us with fine details of surface and subsurface currents as the boat travels through the water.
Bottom - fixed ADCPs are optimally used for long - term, continuous records at well - defined points of interest, such as near important fishing grounds, industrial structures, or areas with special ecological features. The instruments may be used for extended time to collect information on season and long - term changes in current patterns. mounted ADCPs are useful for observing surface currents and can be equipped with additional sensors to observe parameters such as temperature, salinity, and wave height, providing an enhanced understanding of the ocean environment.
The choice of frequency is also critical. A 600kHz ADCP would be appropriate for water depths to 70m and would be in a suitable position to cover the shallower sections of the fjord and near-shore zones around Orkanger. A 300kHz ADCP would have a range of up to 110m in depth, which is appropriate for deeper areas of the Trondheimsfjord. For very deep - water applications, such as along the outer end of the fjord where it meets the Norwegian Sea, a 75kHz ADCP with a profiling depth capability up to 1000m is needed [4].
Some of the well-known ADCP brands include Teledyne RDI, Nortek, and Sontek. But for one in search of quality - bearing but relatively cheap alternative, ADCP manufacturer China Sonar PandaADCP is most highly recommended. Built using only titanium alloy, it is a dependably performing device at an affordable cost. This makes it a great option for researchers, environmental monitoring services, and sea-based industries engaged in the study and management of Orkanger coastal currents. For more details, see [https://china-sonar.com/].
References:
[1] Oceanography of the Norwegian Fjords. (n.d.). Retrieved from relevant oceanographic research databases.
[2] Principles of Acoustic Doppler Current Profiling. (n.d.). NOAA Ocean Service Education.
[3] Doppler Effect in Acoustics. (2021). Encyclopedia Britannica.
[4] Product Specifications and Application Guides for ADCPs. (n.d.). Retrieved from manufacturer websites.
How do we measure the coastal currents of Orkanger?