Measuring and Modeling Internal Wave Properties and Their Effects on High-Frequency Imaging Sonar
Abstract
Our overarching objective for the work proposed is to combine oceanographic data and modeling and acoustic measurements and modeling, to improve our understanding and modeling, inversion, and, if possible, mitigation capabilities for both linear and non-linear inte,rnal waves and related features such as boluses. We also aim to quantify spatial and temporal characteristics of shoaling and breaki,ng internal waves on the inner shelf via inversion of SAS data and to compare these measured characteristics to those predicted by a,nalytical or numerical models as well as emulate their effects on high-frequency imaging and bathymetric sonar systems. These object,ives are based on the proven ability of acoustic systems to directly sense properties related to internal waves as evidenced in the,images below and our previous work on inverting SAS data to obtain quantitative measures of these properties. AUV mounted systems ca,n offer large area surveys of internal wave features as they move into and on the inner shelf, including their 3D shape. Fixed acous,phic and acoustic modeling. The ability to make measurements via SAS or fixed location systems over many days would allow the dynami,cs of shoaling internal waves to also be measured, e.g., frequency, forcing, speed, change in speed, size, and change in shape. Inte,rferometric SAS system offer the ability to measure co-located high-resolution bathymetry so that the dynamics of shoaling internal,waves could be directly related to the 3D topography along inner shelf regions. It is not an understatement to say that the proposed, novel high-resolution measurements provided by the SAS systems would yield a previously unattainable level of detail on linear and,non-linear waves in shallow water which would be a huge addition to data collected by traditional ship-based measurements of oceanic, properties.Aside from the important oceanographic effects mentioned above, of most interest to the Navy are the degrading effects t,hat internal wave features such as boluses have on high-resolution imaging sonar systems used in MCM target detection and classifica,tion. Internal waves and related features such as boluses change the water column sound speed structure and therefore will affect im,ages of the seafloor by focusing or defocusing transmitted acoustic energy. Shadows in areas of defocus, can make any targets esse,ntially invisible as there will be little acoustic energy hitting regions,t patches which may cause issues for ATRs in a similar fashion to ripple fields. Coherent and incoherent change detection, which are, currently being explored by other ONR research programs as a possible method for target detection, would also be negatively impacte,d by shoaling internal waves and related features. Change detection compares images taken at different times to optimally detect cha,nges in each scene. Propagating features in the water column would cause differences between images acquired at different times, adv,ersely impacting target detection using change-detection methods. A more complete understanding of linear and non-linear shallow-wat,er internal waves and their interactions with topography, such as shoaling and breaking, is therefore absolutely required to aid in,the development of techniques designed to detect and mitigate the impacts of internal waves on naval sonar systems and to provide a,predictive capability for use in operational planning and performance estimation. Synthetic aperture sonar based high-resolution int,erferometric bathymetry will also be adversely affected by internal waves and related features (e.g., boluses).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Dec 10, 2021
- Source ID
- N000142212030
Entities
People
- Anthony P. Lyons
Organizations
- Office of Naval Research
- United States Navy
- University System of New Hampshire