## 2 The Experimental Data  
In this study, we utilized the raw data of two 2D seismic lines of the EMED and ISEM surveys offshore Israel (Figure 1). EMED data were acquired by Spectrum Energy & Information Technology Ltd. of Woking, Surrey, UK, onboard the R/V Geo Baltic on 11 July 2000 (EMED-003) and 2 September 2000 (EMED-054), using a 7200 m-long HLA of 576 hydrophones with 12.5 m spacing that started at an offset (i.e., the distance from the source) of 150 m and was towed at a depth of 10 \(\pm\) 1 m. Nine-seconds-long signals were recorded at the sampling interval of 2 ms. The sound was radiated with a Sodera G-Gun consisting of 4 sub-arrays of air guns with a working pressure of 2500 psi and located at a depth of 6 \(\pm\) 0.5 m, with a shooting interval of 50 m. ISEM data were acquired by TGS-Nopec Geophysical Company onboard the R/V Northern Access on 11 November 2001, using a 7200 m-long HLA of 576 hydrophones with 12.5 m spacing that started at an offset of 150 m and was towed at a depth of 5 m. Nine-seconds-long signals were recorded at the sampling interval of 2 ms. The sound source consisted of 4 sub-arrays of air guns with a working pressure of 2500 psi and located at a depth of 5 m, with a shooting interval of 25 m. The source signal bandwidth was 20 and 70 Hz with a peak frequency of 35 Hz (Figure 3). The raw data were loaded into the Emerson Paradigm seismic processing software and geometry was assigned based on the sources' P190 file coordinates and the HLA layout parameters. Subsequent data processing utilized the Echos modules, including the application of Notch and High-pass filters at the frequencies of 1 and 8-36 Hz, respectively, for noise reduction. The seismic lines were depth-migrated (Figure S1 supplementary information) in order to constrain the depth model to be used in the subsequent analysis of the raw gathers of records from a single source (source gather). A subsequent velocity analysis focused on areas of simple geology (Figure 1), away from significant seafloor structures that might bias the velocity estimations. Areas of simple geology imply relatively monotonous bottom and sub-bottom geological structure and stratification over the entire seafloor stretch that was insonified by the source-receiver layout (the seafloor 'footprint' of this source). Figure 2: Typical sound-speed profiles for the study area, which were calculated by the equation of Chen and Millero from CTD measurements made near the study are in 2018 [54; 55]. These July and November sound-speed profiles were used as the summer- and winter-velocity profiles, respectively, in the top layer of our model. This footprint coverage area extended approximately to half the length of the HLA (i.e., \(L/2=3600\) m; red dashed line in Figure 4a). Travel times of the relevant phases were then chosen, assisted by reduced travel-time displays of the data. The reduced travel time is given by:  
\[T_{reduced}=T_{arrival}-\frac{x}{c_{reduced}}, \tag{1}\]  
where \(T_{reduced}\) and \(T_{arrival}\) are the reduced and original recording times, respectively, \(x\) is the source to the receiver offset, and \(c_{reduced}\) is the reduction in sound speed assumed by the user. The travel-time choices were exported into MATLAB for subsequent comparison with simulations. To consider ray deviation in the water column, characteristic summer and autumn sound speed profiles were calculated from CTD measurements that were obtained near the study area in July and November 2018 [54], using the equation of [PERSON] and [PERSON] [55]. The resulting velocity profile in the water column (Figure 2) was comprised of three layers: (1) a surface layer a with sound speed of 1538 m s\({}^{-1}\) in November and 1545 m s\({}^{-1}\) in July; (2) a sharp summer thermocine at a depth of \(\sim\)30 m in July and \(\sim\)70 m in November, with a minimum at a depth of \(\sim\)400 m; and (3) a slow but constant increase of sound speed with depth. The sound-speed profile becomes independent on the season after \(\sim\)180 m of the water depth.