The long-term MIT-MSEAS goals of the two phases of the S-DUCT effort are to (i) employ and develop our high-resolution MSEAS modeling system in ocean regimes with surface ducts to provide high-fidelity non-hydrostatic/hydrostatic sound speed fields for acoustic studies, (ii) develop and utilize our coupled oceanographic-acoustic probabilistic modeling based on rigorous Dynamically-Orthogonal (DO) differential equations for the stochastic characterization of surface ducts, (iii) employ and advance our coupled Bayesian data assimilation (GMM-DO filter and smoother) for the joint dynamic ocean-physics-acoustics inversion and next-generation tomography, (iv) apply our theory and schemes based on Bayesian mutual information fields to predict the placement of assets that maximize information and optimize the probability of detection, and (v) quantify the sound speed and transmission loss variability in surface duct regions (e.g. mixed-layer depth variations, internal wave effects scattering acoustic energy out of the surface duct, etc.) and investigate models of such effects that are useful for naval applications.