Accurate determination of acoustic ground impedance is essential for predicting sound propagation over outdoor surfaces. However, the measurement process is affected by uncertainties arising from the experimental setup, particularly from variations in source and receiver positioning. The objective of this thesis is to investigate how geometric uncertainties propagate through impedance measurement procedures and influence the resulting acoustic quantities.<\/p>\n
An experiment is conducted to characterize geometric positioning uncertainties under practical measurement conditions. The resulting probability distributions are used as input for the Monte Carlo (MC) uncertainty propagation framework. The uncertainty analysis is performed using a simulation based on the analytical Weyl\u2013Van der Pol sound propagation model. Two impedance deduction approaches from the standard ANSI\/ASA S1.18-2018, namely the template method and the direct method, are investigated, with the template method serving as the main focus. The propagation of geometric uncertainty is analyzed from the measurement setup to the complex pressure ratio, level difference, impedance, and reflection factor. Boundary analysis is used to evaluate worst-case scenarios, and the influence of repeated measurements is investigated through a grouping approach based on multiple geometric realizations.<\/p>\n
The results show that uncertainty arising solely from geometric setup variations is relatively small but strongly frequency-dependent. In general, the uncertainties of both the real and imaginary parts of the impedance are larger at low frequencies than at high frequencies. The resulting frequency-averaged standard uncertainty in the reflection factor remains well below 1 dB.<\/p>\n
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