## 2 Algorithm for Optimal Deployment
### Modeling of the Underwater Acoustic Channel Impulse Response  
The underwater communication channel is characterized by multipaths caused by the acoustic interactions with the sea surface and bottom interfaces, as well as the water medium itself, which causesthe ISI, and resulting in serious distortion of communication signals. The ISI makes demodulation of the communication signal complex and difficult. Therefore, it is necessary to determine the optimal deployment scheme based on the communication PS estimated via communication channel modeling. The model input parameters associated with the ocean environmental information, including sound speed profiles, bathymetry, and sediment properties, are needed for accurate underwater acoustic channel modeling. Here, the bathymetry in the targeted area is extracted from ETOPO1, which is a global relief model of Earth's surface integrating land topography and ocean bathymetry supplied by NOAA (National Oceanic and Atmospheric Administration) [24; 25], with a spatial resolution of ~100 m. The sound speed profiles are extracted from the GDEM (Generalized Digital Environment Model) with a 1/4\({}^{\circ}\) horizontal grid resolution and a monthly time resolution [26]. The values of sediment mean grain size are obtained by interpolating the mean grain sizes measured from surficial sediment samples taken directly from 14 positions within the targeted area. The mean grain size values of the surficial sediment were converted to the sediment sound speed, density, and attenuation coefficient using the empirical formula developed by [PERSON] and [PERSON] [27]. Figure 1a shows the targeted area selected in this paper. The size is 22 km \(\times\) 22 km and its western boundary is ~10 km away from the eastern coast of Korea. The targeted area was divided into 100 grid points, for which environmental data were extracted from the database for eight azimuthal angles (Figure 1b). Figure 2a,b shows the interpolation maps of bathymetry and mean grain size (expressed by \(\phi\), where \(\phi\)\(=-\log_{2}(d~{}/d_{0})\), \(d\) is the grain diameter in millimeters, and \(d_{0}\) is the reference length, equal to 1 mm) for the targeted area. Figure 2c shows examples of sound speed profiles and bathymetries for eight azimuthal angles of a grid point located at 36\({}^{\circ}\) 79\({}^{\circ}\) N and 129\({}^{\circ}\) 68\({}^{\prime}\) E. The deterministic channel impulse responses for the eight azimuthal directions are predicted using BELLHOP, which is a ray-based acoustic propagation model [28]. The BELLHOP model is a highly efficient and rapid acoustic ray tracing model suitable for higher frequency and range-dependent ocean environments. Figure 1: (**a**) Location of the targeted area and (**b**) 100 grid points in the targeted area. The lines in (**b**) indicate the directions of eight azimuthal angles at each point. Figure 3a,b shows the eigenray tracing results for the azimuthal angles of 90\({}^{\circ}\) and 270\({}^{\circ}\), respectively, at a grid point located at 36\({}^{\circ}\) 79\({}^{\circ}\) N and 129\({}^{\circ}\) 68\({}^{\prime}\) E. The eigenray tracing results for the source-receiver ranges of 100 m, 1 km, and 2 km are shown in the top, middle, and bottom plots, respectively. The source and receiver are assumed to be positioned 2 m above the bottom for both azimuthal angles. The main difference between the two different azimuthal angles is that the sound propagates into the up-slope direction for the azimuthal angle of 90\({}^{\circ}\) and the down-slope direction for the azimuthal angle of 270\({}^{\circ}\). Figure 3c,d shows the channel impulse responses as a function of arrival time for the source-receiver ranges between 100 m and 2.5 km for the azimuthal angles of 90\({}^{\circ}\) and 270\({}^{\circ}\), respectively. The first arrival includes direct (D) and bottom (B) paths. The second arrival includes the paths associated with single sea-surface bounce path, such as sea surface (S), bottom-surface (B-S), and surface-bottom (S-B) paths.