Uncertainties in Current Measurements in the Northern North Sea

Abstract

A met-ocean measurement program of waves and current profiles at five locations in the northern North Sea was performed over a period of approximately 5 years. Despite quality control, the measured current speed data contained more noise than expected and large discrepancies were observed between overlapping current speed data measured by different current profilers at the same locations and water depths. Some of the noise and discrepancies can be explained by the influence from surface waves. The current measurements from instruments attached to a surface buoy indicated that these suffered from the influence of surface waves. Further investigations of the uncertainties in current speed data were carried out through three phases of a current verification study, where both additional current measurements and data analysis were done. Comparisons of overlapping measured current speed showed large deviations, suggesting that the accuracy of current measurements is not as good as the user expects. These presented results are in contrast to previous studies of overlapping current measurements.

Simulated wind-generated inertial oscillations compared to current measurements in the northern North Sea

“…Inertial oscillations with smaller Cs are also observed. These wind-generated inertial oscillations resulting in large Cs August 2014 with Cs around 60 cm/s and 80 cm/s, respectively, Bruserud and Haver (2017a) found that the current conditions at Location 1 differ from the three other locations. As Location 1 is located further north in the northern North Sea in an area with steeper bottom topography and larger water depths, than the other 3 locations, other phenomena than wind-generated inertial oscillations such as large-scale current contribute to the current conditions here.…”

“…The measured current data showed that currents from wind-generated inertial oscillations dominate the current conditions in the northern North Sea and also generate the largest observed current speeds (Bruserud and Haver 2017a). Following this, a simple mathematical model for wind-generated inertial oscillations can be applied to simulate current conditions of a longer duration for the northern North Sea.…”

“…1. A brief summary of the measurement campaign is given here and more details can be found in Bruserud and Haver (2017a ADCP and a RDI 1200 kHz Workhorse (WH) ADCP to measure the Cs and CsDir throughout the entire water column and near seabed, respectively. Sea temperature and salinity measurements were also done near seabed.…”

“…The extensive measured wave and current data set from the northern North Sea has been analyzed to describe and give new insight about both the general and inter-annual current conditions at three selected water depths (40 m, 80 m and 3 m above seabed) at the four locations; see Bruserud and Haver (2017a); Bruserud and Haver (2017j) for further details.…”

“…A metocean measurement programme has been performed at five locations in the northern North Sea for nearly five years, initiated early 2011 and completed late 2015 (Bruserud and Haver 2017a; Haver 2017j). However, challenges related to the quality of measured current data have been reported lately and it has been suggested that the accuracy of measured current data might not be as good as the user initially anticipated (Bruserud and Haver 2017g).…”