An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> A. HAMILTONIAN 3D RAY TRACING PROGRAM FOR THE OCEAN (HARPO) <s> Abstract Explosions of 300 lbs of TNT at 1 km depth off Perth, Australia were recorded on Bermuda hydrophones, demonstrating 30 years age the feasibility of global acoustic transmissions. Climate-induced changes in ocean temperature (and hence in sound speed) can be monitored by measuring travel time changes of acoustic signals from remote powerful sources. Warming induced now at the sound axis by CO2 and other greenhouse gases is estimated at 0.005°C per year, too small to be measured locally in the presence of 1°C rms noise from gyre scale and mesoscale fluctuations. The associated rate of decrease in travel time from greenhouse warming (a global measure of temperature rise) is estimated at 0.1 to 0.2 s per year. This climatic signal should be detectable above the gyre and mesoscale noise (less than 1 s rms), given a program of measurements carried out over a decade. An acoustic source at Heard Island in the south Indian Ocean has direct oceanic paths into all five ocean basins—westward to South Georgia... <s> BIB001 </s> An Overview of Next-Generation Underwater Target Detection and Tracking: An Integrated Underwater Architecture <s> A. HAMILTONIAN 3D RAY TRACING PROGRAM FOR THE OCEAN (HARPO) <s> Abstract : Ray equations based on an acoustic Hamiltonian, and formulated by Jones et al. (1986) for spherical coordinates in NOAA's three dimensional ray tracer HARPO, are adapted to ellipsoidal coordinates in the oceanic waveguide. The ensuing modified HARPO is used to model very long range (up to antipodal) acoustic paths in which the difference between geodesics and great circles is measurable. The eventual objective of this modeling is to extract the predictable part of the travel time trend and fluctuations along several long paths that will be used to monitor hypothetical global warming effects. The requirements for easy assimilation and representation of realistic environmental inputs are discussed. These requirements, when coupled with the possibility of classical chaos in the ray paths, dictate a new software architecture. We use the existing software, however, to breadboard and test features of new ray tracers in the global boundary layer, and to support the experimental design of a forthcoming pilot experiment that will use a transmitter located at Heard Island in the Indian Ocean near Antarctica. <s> BIB002
HARPO is a fully 3D ray tracing program to model very long-range acoustic paths for long-term monitoring of global warming effects. This concept of long-range ocean warming was described by Munk and Forbes BIB001 and summarized by Gibbons  . The longest paths reveal some chaotic behavior that need to be suppressed by using this tracing model; however, the suppression degrades the model practicality. VOLUME 7, 2019 Also, 3D modeling is more likely to create chaotic behavior than 2D modeling; nevertheless, 3D modeling keeps the practicality of the model. HARPO has the characteristic to solve Hamilton equation on an elliptical Earth. But, these calculations of ray paths on curved Earth present complexities. Six variables are used to define ray trajectory in 3D by using non-linear Hamiltonian equations, where three define the position (radius, colatitude, longitude) and other three define the local components of the wavenumber. The interest of the developers of HARPO is to model the long-range sound propagation topology closely related to the geometry of the planet as it provides best topology. The accuracy of the model is limited to moderate ocean environment and it does not consider bathymetry effects. Also, HARPO does not generate eigenrays products (e.g., transmission loss, multipath travel time, phase, and propagation direction). Alternative software is still required to overcome the flaws of HARPO as it does not seem to be a viable model for long-range monitoring when it comes to execute it for non-smooth oceanic medium BIB002 .