Uncertainties in Current Measurements in the Northern North Sea

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.