How much sound does a vegetated roof absorb? To answer that question an appropriate measurement method is needed. In our recently published Applied Acoustics paper by Chang Liu, Fotis Georgiou and Maarten Hornikx, the acoustic impedances of greens roofs were retrieved by fitting parameters of a surface impedance model by measurents on the roofs. It is shown that a combination of multiple source-microphone configurations does lead to a unique prediction of the impedance model parameters, yielding predictions of the absorption of the vegetated roof between 200 Hz and 1600 Hz. Interested? The open access paper can be found here