Empirical fit of the noise model, ηd(x) + υ^ron, directly from the data. Panel a: Visualisation of the arcs centred on the main object on which the model is fitted. Panel b: Approximated map of the noise after removing a median filter on the data. Panel c: Estimated noise model (black curve) compared with the true model (dashed curve). In blue (resp. red): points that are kept (resp. discarded) by the robust fit. The green box is a zoom on the relevant points.