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 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 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 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.