  Due to swish and thump amplitude modulation, the noise of wind turbines cause
more annoyance than other environmental noise of the same average level. The
wind shear accounts for the thump modulation (van den Berg effect). Making use
of the wind speed measurements at the hub height, as well as at the top and the
bottom of the rotor disc (Fig.1), the non-standard wind profile is applied. It
causes variations in the A-weighted sound pressure level, LpA. The difference
between the maximum and minimum of LpA characterizes thump modulation (Fig.2).
