  Full 3D inversion of time-domain Airborne ElectroMagnetic (AEM) data requires
specialists' expertise and a tremendous amount of computational resources, not
readily available to everyone. Consequently, quasi-2D/3D inversion methods are
prevailing, using a much faster but approximate (1D) forward model. We propose
an appraisal tool that indicates zones in the inversion model that are not in
agreement with the multidimensional data and therefore, should not be
interpreted quantitatively. The image appraisal relies on multidimensional
forward modelling to compute a so-called normalized gradient. Large values in
that gradient indicate model parameters that do not fit the true
multidimensionality of the observed data well and should not be interpreted
quantitatively. An alternative approach is proposed to account for imperfect
forward modelling, such that the appraisal tool is computationally inexpensive.
The method is demonstrated on an AEM survey in a salinization context,
revealing possible problematic zones in the estimated fresh-saltwater
interface.
