Strömmar

Den akustiska strömmätaren på tröskeln in till Byfjorden är upptagen eftersom projektet är avslutat.

The current-meter is now recovered since the project is finished. A current profiler has been placed at the sill of the Byfjord. The instrument is located att approximately 14 metres depth. The profiler is an ADCP which stands for Acoustic Doppler Current Profiler. As the name implies the current above the instrument is measured acoustically by emitting a sound pulse. When the pulse hits particles in the water it is reflected back to the instrument where it is registered. By using the knowledge of the Doppler Effect the instrument can calculate the velocity and direction of the particle. As the particles is assumed to move with the same speed as the true current they therefore act as proxies. Depending on the time from a pulse is emitted to it returns by reflection the instrument also calculates the distance, and hence the depth of the current. A sound pulse is emitted a few times per minute. Below you can study the last seven days of current measurements. The contour plot shows all measurements over the past week into (redish colours – positive values) and out of the fjord (blueish colours – negative values). You can easily distinguish the regular in/outflow pattern created by tidal movements.  The thick blue line denotes the water surface. Click on the figure for a larger version.