This paper quantifies the system damping of a offshore meteorological mast supported by a Mono Bucket foundation based on a long-term experimental campaign. The structure is located at Dogger Bank west, North Sea, and equipped with a measurement system monitoring acceleration, strain, inclination and sea surface elevation. Natural frequencies and corresponding damping ratios are assessed using different operational modal analysis techniques, enhanced frequency domain decomposition and stochastic subspace identification. Application and results from both methods are compared and discussed. Research shows that the total damping ratio of the lowest eigenmode is normally distributed with mean value of 1.11% of critical damping. Linear correlation between the damping ratio and the significant wave height is observed.