Passive acoustic sensing of the ocean

Underwater signal processing and signal detection schemes require well characterized spatial and temporal ambient sound field properties to operate effectively. Additionally, a detailed understanding of the sound field in the ocean has led to the development of passive methods for querying physical properties of the ocean, seabed and sub-bottom as well as investigation into the fundamental physics and statistics of sound source mechanisms such as wave breaking, rainfall, and earthquakes. Recently, ambient sound has been used to study the ecological health of the oceans, from tracking individual animals to monitoring the acoustic activity of entire ecosystems. Ocean technology development, at-sea data collection, ocean observatories, and acoustic modelling efforts will be combined in support of a long-term research program on the generation, propagation, and nature of ambient sound in a complex ocean environment. The objectives of this program are to develop and demonstrate signal processing methods for dissecting the underwater sound field and retrieving oceanographic information from passive acoustic recordings and to answer the question "What can we learn about the ocean by listening?" The complimentary objective is to improve and validate analytical and portable computational noise models, or ask "How can we predict ocean noise?" Over the proposed research period, autonomous recording platforms will be deployed in support of several field campaigns. They will be used in the acoustic monitoring of hydrothermal vents, passive acoustic inversions of seawater and seabed properties, and the exploration of deep ocean trenches. The platforms carry small acoustic arrays capable of assigning energy in the soundscape to persistent (breaking waves, distant shipping) and transient (local shipping, animals) sources. This source partitioning method allows the precise estimation of the human-made contribution to the marine soundscape. The measurement of the spatial variability of noise can be used to characterize the ocean. A method for inferring the depth integrated ocean acidity from a profiling acoustic vehicle will be validated. A simple method for measuring seawater pH over large areas (~ 10's of km^2) is required for monitoring carbon sequestration efforts key to reducing the effects of global warming and climate change. Passive listening methods will also be used to measure the composition and structure of the seafloor and nature of the ice canopy, and to remotely sense properties of hydrothermal vents. Accurate source levels per unit area of wind generated wave noise and rain fall noise are required as inputs to predictive portable ambient noise models. Applying source partitioning methodologies to long-term data sets collected at ocean observatories will improve estimates of these parameters and quantify their uncertainty. Real-time acoustic observatories will be used to develop a data-assimilative noise forecast for the Salish Sea.