Multi Channel Measurements for the Qualification of Noise Barriers In Situ, Discussion of Uncertainty Factors Gottfried K. Behler a) Pascal Dietrich b) Michael Vorländer c) Institute of Technical Acoustics, RWTH Aachen University Neustraße 50, D-52056 Aachen, Germany In the context of the European FP7 research initiative in 2009 the project QUIESST (QUItening the Environment for a Sustainable Surface Transport) was scheduled [1]. The aim of this project is the assessment and optimization of noise barriers. A certain focus is set onto the acoustic behavior and its characterization. The existing and established measuring method Adrienne (ISO 1793) shall be improved and replaced by a new and more reliable multichannel approach in future. The old standard defines a sequential scan of the barrier using single channel measurements in order to derive the reflectivity of the surface. The new approach shall measure 9 distributed locations in front of the wall at once, thus leading to a faster and more reliable result. For the application of the method several aspects e.g. the source directivity and angle dependent reflection properties have to be investigated. A detailed model of the measurement scenario is used in this work to analyze uncertainties separately. The method will be discussed with respect to the signal processing demands and the limitations created by the multi-microphone array technique. 1 INTRODUCTION The basic principle of the applied measurement system goes back to the idea of measuring absorption coefficients on location by separating the reflected sound from the incident sound by a subtraction method combined with windowing technique [2]. The subtraction was introduced to allow a very close placement of the microphone in front of the surface under investigation so to reduce effects of limited samples size. This leads to overlapping signals (incident and reflected sound) with a very short time delay. For the separation of the reflected portion the incident sound a) Email: gkb@kustik.rwth-aachen.de b) Email: pdi@akustik.rwth-aachen.de c) Email: mvo @akustik.rwth-aachen.de