Conventionally, modal monitoring of Wind Turbine Rotor Blades is primarily based on the evaluation of
eigenfrequencies. Beyond this, combining a sensor network with the Operational Modal Analysis (OMA)
method, mode shape and parallely a local component are utilized here. In addition it is expected that the
damping, which is also determined by the OMA method, will give a lead on damage development at the rotor
already at an early stage. Modal monitoring by means of measurement is combined with FEM simulation and
with the comparison of results obtained from measurement and simulation. Moreover, this will establish a
connection between the engineer and the design data of a rotor blade, which also are based on FEM analyzes.
A further significant increase regarding error resolution is possible by combining the global modal methods with
locally sensitive monitoring methods, based on guided elastic waves. These assume plate-like structures through
which elastic waves propagate in the low-frequency ultrasonic range (10 - 100 kHz) in certain modes. These
different wave modes interact distinctively with inner structural damages such as web fractures and
delaminations. It is differentiated between piezoelectrically excited waves (acousto ultrasonics), and waves
produced by energy released at fractures, delamination etc. (acoustic emission). Applying a moderate number of
sensors, the combination of both methods can allow an effective monitoring of the global structure.