shallow water, which exhibits a strong in?uence by the cutoff frequency. It has an even larger effect on the modelled ef?cieny of mitigation systems. The ef?ciency of the mitigation strongly depends on the source pro?le, since the attenuation is frequency dependent, with maximum reduction at mid frequencies (300–4000 Hz). Using a different source pro?le derived from Bellmann et al. (2020) altered the results. Further issues that add to the uncertainty of results result from the interaction with the seabed, which is site speci?c and in?uences the contribution of the sea-bottom thus altering the performance of the mitigation system. Using unrealistic source spectra potentially introduce deviations of about 10 dB in the estimate of the ef?ciency of the mitigation system. Conclusions As result from the data harmonization, regional case studies, and quality assessment, it was demonstrated that a quantitative assessment of exposed marine habitats by impulsive sound based on available data in noise registries would be directly applicable for all EU regions and sub-regions. Further, a time-dependent assessment of the environmental status regarding D11C1 for different time-scales was identi?ed as a realistic goal for a harmonized assessment approach in all marine areas within EU MSFD responsibility. A key characteristic of the habitat-based approach identi?ed as basis for harmo- nization was its potential to assess and limit impacts due to underwater noise by setting spatial and temporal thresholds for noise in certain habitats or parts of habitats (e.g., national reporting units, subregional units). Furthermore, the approach can be applied in line with the precautionary principle. For preventing impacts on marine Fig. 4 In?uence of the bottom properties on the acoustic propagation in a shallow-water context at 63 Hz 16 C. Juretzek et al.