Monitoring of blades in wind turbines

A method for detecting a status of a rotor blade for a wind turbine, the rotor blade including at least an aerodynamic device for influencing an airflow flowing from a leading edge to a trailing edge of the rotor blade, the aerodynamic device being movable between a first configuration and a second configuration, the method comprising:

• measuring an output signal measured by at least one sensor installed on the wind turbine;
• moving the aerodynamic device between the first configuration and the second configuration;
• measuring a change in the output signal induced by the moving of the aerodynamic device between the first configuration and the second configuration;
• post-processing the measured output signal for performing an analysis of the change in the output signal, wherein the post-processing step is performed in a frequency domain and includes:
• deriving a frequency spectrum of the output signal, and
• calculating an upper spectrum interval of the frequency spectrum above a frequency threshold value, wherein the frequency threshold value is a frequency at which an amplitude of the frequency spectrum starts decreasing rapidly when the aerodynamic device is in the first configuration, and the upper spectrum interval includes amplitudes at frequencies greater than the frequency threshold value when the aerodynamic device is in the second configuration;
• comparing the upper spectrum interval with a reference frequency spectrum above the frequency threshold;
• and
• deriving a status of the rotor blade based on the comparing.