rated to be not in line with current assessment priorities and the regional focus of the MSFD. Hence, a quantitative assessment of marine habitats and marine regions exposed to impulsive noise on the basis of available data in noise registries was evaluated to be directly applicable and feasible for all EU regions and sub-regions. Further, an assessment of the environmental status regarding D11C1 on different time scales, i.e., ranging from days to years, was identi?ed as realistic ambition level for a harmonized assessment approach in all marine areas within EU MSFD responsibility. The general procedure of an immediately applicable assessment approach is described by the following steps (Müller et al. 2021): • De?nition of the Management Area (MA), e.g., Marine Reporting Units (MRU). • Determination of the assessment area/habitat of the indicator species. • Evaluation of completeness and quality of the data. • Determination of Level of Onset of Biological adverse Effect (LOBE). • Selection of a propagation model to estimate sound pressure ?elds, effect ranges, or scienti?cally justi?ed effect ranges (prede?ned ranges). • Determination of the temporal and spatial noise pressure. • Calculation of exposure using assessment/habitat area and noise pressure and determining the exposed habitat (% area and time exposed). • Assessment of the environmental status based on threshold values for tolerable temporal and spatial exposure. Decision Scheme for Noise Propagation Modelling The general objective of the noise propagation modelling in the context of the D11C1 assessment is to quantify the spatial exposure of noise-sensitive species in marine habitats due to one or more impulsive sound events. Sound propagation from a sound source to a receiving point is largely determined by various parameters including the source location and duration, the source depth, the type of source, the source spectra and distribution of energy, the bathymetry and seabed, the oceano- graphic conditions (such as temperature and salinity), currents, tides, the weather conditions such as wind and waves and the receiver location. An important prerequisite for harmonization was that the determined exposed areas (in 2D) or the volume (in 3D) are comparable, i.e., lie in the same result range, regardless of the sound propagation modelling approach used. To achieve such comparable results, also the input data have to be well de?ned and accurate. For the selection of appropriate propagation models in a regional assessment, a decision scheme was developed as illustrated in Fig. 2. The decision scheme follows four interlinked steps (Müller et al. 2021), which are summarized in the following. Scope of application: Depending on indicator species and marine region, the approach for the noise propagation modelling needs to consider that: 8 C. Juretzek et al.