A system and method for the verification and calibration of wind turbine sensor systems is provided. The system comprises an optical capture device provided on a wind turbine which is arranged to record the position of at least one light source provided at the wind turbine during operation of the wind turbine. The motion of the light source relative to the optical capture device can provide an indication of relative motion of a portion of the wind turbine during operation, which can then be used as an input to a calibration and/or a verification system for a sensor system of the wind turbine.