A method of estimating a position of at least a part of a rotor blade of a rotor of a wind turbine during operation of the wind turbine is provided. The rotor blade is deflected due to a deflection motion of the rotor blade towards a tower of the wind turbine and the position is indicative of the deflection. The method includes measuring a first parameter indicative of an absolute and/or a relative position of at least a second part of the rotor blade or of a further rotor blade of the rotor. The method further includes measuring second parameters indicative of an absolute and/or a relative position of at least a third part of the rotor blade or of the further rotor blade of the rotor. The method further includes estimating a state of the rotor blade and deriving the position from the estimated state of the rotor blade.

The present disclosure is related to methods for determining a frequency of an oscillation mode of a wind turbine, comprising: determining a motion of a first mass of a first tuned mass damper in the wind turbine and deriving the frequency of the oscillation mode of the wind turbine at least partially based on the determined motion of the first mass. The present disclosure further relates to methods for operating a wind turbine, and to wind turbines, particularly offshore wind turbines, comprising tuned mass dampers.