  This paper proposes a framework for the estimation of the transport and
elastic properties of open-cell poroelastic media based on sound absorption
measurements. The sought properties are the Biot-Johnson-Champoux-Allard model
parameters, namely five transport parameters, two elastic properties and the
mass density, as well as the sample thickness. The methodology relies on a
multi-observation approach, consisting in combining multiple independent
measurements into a single dataset, with the aim of over-determining the
problem. In the present work, a poroelastic sample is placed in an impedance
tube and tested in two loading conditions, namely in a rigid-backing
configuration and coupled to a resonant expansion chamber. Given the
non-monotonic nature of the experimental data, an incremental parameter
estimation procedure is used in order to guide the model parameters towards the
global solution without terminating at local minima. A statistical inversion
approach is also discussed, providing refined point estimates, uncertainty
ranges and parameter correlations. The methodology is applied to the
characterisation of a sample of melamine foam and provides estimates of all
nine parameters with compact uncertainty ranges. It is shown that the model
parameters are retrieved with a lower uncertainty in the multi-observation
case, as compared with a single-observation case. The method proposed here does
not require prior knowledge of the thickness or any of the properties of the
sample, and can be carried out with a standard two-microphone impedance tube.
