Whereas usual meteorological observations, such as satellite images or surface temperature measurements, are instantaneous, the low frequency sounds propagates in the atmosphere during long time scales (>1000 s), and so cannot be considered as instantaneous. We present here how the sensitivity of acoustic wave observations, such as propagation time, varies with space and time along its propagation in the atmosphere. Consequently, we compute where the different time steps of an atmosphere model are sensitive to the same acoustic observation. Examples are provided for infrasound generated by a surface explosion and recorded 300 km away. We also discuss how the current atmosphere modelling methods can take into account these observations spreading their constraints over time and space.