A method of operating a wind turbine , the wind turbine comprising a rotor with one or more pitch adjustable rotor blades , where each blade comprises a pitch actuator for adjusting the pitch angle (θ), the method comprising: actively promote blade vibrations by imposing a pitch actuation signal to the pitch actuator ; determining at least one parameter relating to the blade vibration, the rotor is rotating a controlled speed, and wherein the active blade vibration promotion is conducted while the rotor is rotating; characterized in that the active blade vibration promotion is conducted by: receive an edgewise load signal (BL 1 , BL 2 , BL 3 ) for each of the adjustable rotor blades, the edgewise load signal being measured in a rotating reference frame; apply an m-blade coordinate transformation (T) to the edgewise load signal to transform the signal to a whirling reference frame along a first and a second reference direction (s 1 , s 2 ); select the signal component of either the first or the second reference direction to obtain a selected signal component (s); filter the selected signal component at either a backward whirling frequency or a forward whirling frequency to obtain a filtered signal component (fs); apply an inverse m-blade coordinate transformation (T -1 ) to the filtered signal component to obtain the pitch modification signal; set the pitch modification signals as the pitch actuation signals for each blade to actively promote blade vibrations. actively promote blade vibrations by imposing a pitch actuation signal to the pitch actuator ; determining at least one parameter relating to the blade vibration, the rotor is rotating a controlled speed, and wherein the active blade vibration promotion is conducted while the rotor is rotating; characterized in that the active blade vibration promotion is conducted by: receive an edgewise load signal (BL 1 , BL 2 , BL 3 ) for each of the adjustable rotor blades, the edgewise load signal being measured in a rotating reference frame; apply an m-blade coordinate transformation (T) to the edgewise load signal to transform the signal to a whirling reference frame along a first and a second reference direction (s 1 , s 2 ); select the signal component of either the first or the second reference direction to obtain a selected signal component (s); filter the selected signal component at either a backward whirling frequency or a forward whirling frequency to obtain a filtered signal component (fs); apply an inverse m-blade coordinate transformation (T -1 ) to the filtered signal component to obtain the pitch modification signal; set the pitch modification signals as the pitch actuation signals for each blade to actively promote blade vibrations. receive an edgewise load signal (BL 1 , BL 2 , BL 3 ) for each of the adjustable rotor blades, the edgewise load signal being measured in a rotating reference frame; apply an m-blade coordinate transformation (T) to the edgewise load signal to transform the signal to a whirling reference frame along a first and a second reference direction (s 1 , s 2 ); select the signal component of either the first or the second reference direction to obtain a selected signal component (s); filter the selected signal component at either a backward whirling frequency or a forward whirling frequency to obtain a filtered signal component (fs); apply an inverse m-blade coordinate transformation (T -1 ) to the filtered signal component to obtain the pitch modification signal; set the pitch modification signals as the pitch actuation signals for each blade to actively promote blade vibrations. <EOS>