Mitigation of low-frequency groundnoise from runways

With the extra runway at Amsterdam Schiphol Airport, introduced in 2003, the noise nuisance for local residents increased due to increased groundnoise. In a case study the effect of enhanced ground absorption on the propagation of low-frequency noise from aircraft ground operations, e.g. departing aircraft, has been investigated. The study was initiated by Amsterdam Schiphol Airport, and has been performed by TNO and Alterra. By means of ground impedance measurements, performed at areas of 200 by 200 m near the runway, it was demonstrated that a ploughed ground surface shows an increased ground absorption compared to an unprocessed ground surface. The frequencies of interest are mainly in the 31 and 63 Hz octave bands. Further, is has been shown numerically that for propagation distances up to 3 km from the runway a noise reduction of 5 to 10 dB can be achieved if such a ploughed ground is employed. This reduction occurs for downwind conditions when the sound levels are highest. The study has contributed to the discussion of the airport and the residents in their search for a solution and to the understanding of the effects of airborne groundnoise.