Sonobuoy Improvements for Multistatic Active Sonar -- 21-013

The U.S. Navy’s Multi-Static Active Coherent (MSAC) sonobuoys provide a critical capability for battlespace awareness. Active source buoys (such as the AN/SSQ-125) and receive buoys (such as the AN/SSQ-101 ADAR buoy) stream information to the P8 aircraft platform where sonar operators use advanced tactical decision aids (TDA) to detect, classify, localize and track undersea targets. Several physical factors can conspire to undermine the performance of this processing chain, which stem from a lack of reliable information about the state of the buoys and of the surrounding oceanography. To that end, Metron and APL-UW propose to add motion and temperature sensors to the AN/SSQ-125 source sonobuoy. These sensors will provide a direct measure of array tilt, give some insight into buoy drift, and provide much greater spatial and temporal coverage of sound velocity field over the operation area (OPAREA). Monte Carlo simulations will be used to assess the extent to which these measurements can improve the accuracy and reliability of detection processing, with an objective of a 25% improvement. The proposed team has gained specific experience in MSAC data analysis and environmental modeling through a NAVAIR-sponsored STTR titled Detection Rate Improvements Through Understanding and Modeling Ocean Variability (N18A-T002). In that project, which is now in Phase II, the same team consisting of Metron and APL-UW are investigating the physical and oceanographic causes of transmission loss (TL) variability, with the goal of producing physics tools that will improve TL modeling accuracy. Key insights gained from that research suggest that unmodeled source buoy tilt, coupled with differences between ocean models and the actual ocean environment, are together responsible for often-observed large, unexplained, fluctuations in TL. This can happen in certain environments in which the source buoy, which is a vertical line array with a directional beam pattern, projects its acoustic energy through the environment in unexpected ways. Tilt information can be used to flag questionable pings, improve acoustic predictions, or even potentially adjust each ping produced from a tilted array in real time so as to stabilize its radiated beam pattern. These approaches are listed in order of difficulty and sophistication, and the proposed work plan addresses each of them in stages.