Geometrically constrained underwater environments abrogate the simplifying acoustic modeling assumption that energy can be modeled in a two-dimensional vertical plane. In these environments, current tools to perform navigation and passive and/or active sonar mission planning are inadequate. Furthermore, channel complexity makes it difficult to model acoustic communications. HRC proposes to upgrade the current Navy Standard Comprehensive Acoustic System Simulation, currently used in the Navys tactical decision aids for ASW sensor performance predictions and Acoustic Communications planning, to model propagation loss, reverberation, performance, and communications effectiveness in complex, 3-dimensional environments. HRC and its academic partner, ARL:UT, will first design upgrades to the reflection and scattering modeling and bookkeeping in the model, implementing upgrades in a prototype that will then be compared to academic, closed-form, and/or measured data sets, to determine the level of fidelity achieved by this initial set of upgrades. Next, the one-way propagation loss and eigenray model will be upgraded and validated. Once the modeling has been completed and validated, it will go through the Navys OAML process, during which the upgrades are subject to independent validation, and then implemented in Navy sensor performance and communication prediction systems, and through OAML, be made available for additional DoD applications.
Benefit: The primary benefit of an efficient, accurate, 3D propagation model is that it can provide useful sensor performance, navigation, and communications predictions in a larger range of environments than is currently possible. Furthermore, because our proposal suggests the use of a current Navy standard model, the process of approving improvements to this model will be streamlined. Finally, because the CASS and GRAB models are not only high fidelity but also efficient, the extension to a full 3D environment should provide a model that combines the accuracy needed by operational scenarios with the speed needed for the pace of operations. By the end of Phase II we will have a 3D propagation model for use in the 3D performance prediction model when necessary, a good sense of when a 3D propagation model is necessary, and a simpler, and faster, Nx2D propagation model otherwise. Commercialization strategy involves both government and private uses: Collision avoidance in constrained environments Improved Marine Mammal protection Ocean database development While private use of this model will require US government permission, there is significant precedent for this in the release of the CASS/GRAB model to several foreign countries; at this point, CASS and GRAB are used as academic benchmarks as well as tactical decision aids by many universities, laboratories, and operational commands. The models are owned by the US Government, completely free from any proprietary or classification issues. Additionally, the current model architecture allows for an executable that can be compiled and released without sharing source code, a fact that improves the likelihood of release to third parties in many cases. One possible commercial application for the 3D model is in collision avoidance. As sonar systems on exploration and transport ships become more sophisticated, gaining the ability to not only detect bottom depth using a fathometer, but to use side-scanning sonars, three-dimensional propagation can become significant in complex, constrained environments. The use of sonar as an adjunct to visual and radar cues can improve ship safety in conditions such as heavy fog and bad weather, especially when he use of sonar is in conjunction with a 3D propagation model. Another potential commercialization opportunity is in controlling the damage to marine mammals by active sonar systems, and possibly from collisions with military and nonmilitary surface ships. A mid-frequency 3D propagation model could be used to estimate the propagation of active sonar pulses into constrained environments, and the strength of the signal as it attenuates in the environment. In areas where horizontal refraction and near-vertical boundaries contribute to the focusing of energy, the 3D model will provide higher-fidelity results than will any Nx2D model. Collisions with mammals can be minimized when mammals are audible on sonar, by using the better localization estimates provided by a 3D model. When mammals are detectable with active sonars, the same principals can be applied to better estimate where the mammals are, and the active CASS can be used to predict when and at what range mammals, or groups of mammals, will be detectable in constrained environments. A third, strong possibility, is to use a 3D propagation and reverberation model upgrade The Naval Oceanographic Offices (NAVOCEANO) ability to create environmental databases. Currently, NAVOCEANO uses the Navy Standard PE model to invert acoustic measurements to estimate low-frequency bottom loss parameters. With a 3D model, these parameters, and high-frequency bottom loss parameters could be generated more accurately in complex, constrained environments.
Keywords: Complex Acoustic Environment, Complex Acoustic Environment, OAML, 3-D Acoustic Modeling, Eigenrays, Reverberation, CASS/GRAB, Scattering
