The choice of the frequency discretization during the calculation of the propaga- tion had a signi?cant impact on the precision of the calculation. While the average deviations observed were close to zero, differences of up to 20 dB appeared locally. It is possible that these deviations affect the surface layers and the deep layers more frequently. The choice of an appropriate frequency discretization for sound propa- gation calculations hence corresponds to a compromise between the desired accu- racy of the results and the time allocated to the calculation. Test case 2 addressed underwater explosions in the Baltic Sea. Underwater explosions occur in different contexts (e.g., civil engineering such as rock excava- tion or fragmentation before drilling, military activities such as detonations of unexploded ordnance or ship shock trials) and are among the noisiest man-made activities in the seas. The objectives of this test case were to analyze the effect of sediment variability, the effect of bathymetry, the in?uence of source pro?les, and the frequency dependence of underwater propagation as described in Table 4. The joint in?uence of sediment variability and bathymetry has a strong impact on sound propagation, as demonstrated by the choice of two different bottom types (rock or sand) and two different bathymetric pro?les for the modeling of scenarios 02A-B-C-D. Figure 4 shows the in?uence of the bottom properties on the acoustic propagation in a shallow-water context at 63 Hz. Overall, the rocky-type sediment was found to be more favorable for sound propagation, especially at low frequencies. The difference in transmission loss with respect to the sandy-type sediment reaches 80 dB for the lowest frequency of 32 Hz. This causes a difference on the broadband level received at 100 km from the sound source of up to 35 dB. These results highlight two strong in?uenceing factors on the propagation of sound: the cutoff frequency onone hand, which has the effect of blocking the propagation of energy below the cut-off frequency. The value of which depends on the water level and the type of sediment. The second phenomenon is the interaction of the acoustic wave ?eld with the seabed. The re?ection coef?cient determines the proportion of energy that is re?ected back into the water column and thus not lost in the sediment. At long distance, the repeated interactions of sound and the seabed make the effect of the re?ection coef?cient signi?cant. Further, comparison of two different modeled source pro?les has highlighted the importance of including the frequency distribu- tion of the acoustic energy emitted by the source in the assessment. Test case 3 addressed pile driving activities in North Sea, which involves repeat- edly pounding long steel pipes into the ocean ?oor to support other structures, such as bridges, piers, and wind turbines (Table 5). A large hammer is used to strike the top of the pile, generating vibrations in the air, water, and sediment. The objectives of this test case were to study the effects of different technical noise abatement measures and their effectiveness depending on the source pro?le used. Details on technical noise mitigation solutions and examples of their associated mitigation effectiveness as observed at speci?c sea sites as also used in this case study are described in a cross-project experience report for offshore windfarm construction projects in Germany (Bellmann et al. 2020). The considered source spectrum has a large effect on the modelled distribution of the underwater noise generated at the pile. Mainly because piling is performed in 14 C. Juretzek et al.