Noise in the PACS-100 μm (top panel) and PACS-160 μm (bottom panel) maps as a function of exposure time. Empty circles represent the total noise σ_T of the maps. The total noise is fitted with two noise components added in quadrature: an instrumental noise σ_I component following a t^-0.5 trend (dashed line and empty squares) and an constant confusion noise σ_c component. The dotted lines present the two components fitted to σ_T. The dot-dashed lines present the two components fitted to σ_T made in Berta et al. (2011) and illustrate the smaller exposure time range probed in their study.