Field G300.86-9.00 as an example of the τ(250 μm) bias estimation with radiative transfer modelling. Upper row: relative error between the model predicted surface brightness and the observations at 250 μm, 350 μm, and 500 μm. Lower frames: colour temperature and τ(250 μm) maps calculated from the synthetic observations and the relative bias in τ(250 μm) obtained by comparison with the actual τ(250 μm) values in the model.