Targets encountered during synthetic aperture sonar (SAS) surveys may exhibit elastic scattering behavior and re-radiate sound after initial interrogation. These re-radiated returns are often described as “late-time” energy, as they reach the sonar after the initial geometric returns. Range-specific focusing methods can enhance acoustic features such as late-time energy, but these methods typically make a monostatic sonar approximation that may not hold in very shallow water sensing geometries. This presentation will discuss the development of a late-time reconstruction algorithm applicable to bistatic sonar geometries. Using both simulated and experimental sonar data from monostatic and bistatic collection geometries, this work will first quantify the differences between traditionally beamformed imagery and late-time-focused imagery using common image quality metrics. Next, we will quantitatively compare the impact of collection geometry on the performance of late-time focusing algorithms. Finally, the work will describe methods that use information from a multi-static collection to compress late-time energy down to a high-contrast, spatiallycondensed point. The analysis of these signal processing strategies will focus on their potential applications to automatic target recognition.

An electronic speckle pattern interferometer (ESPI) is an optical system used to investigate vibrating objects and can be a great educational tool for visualizing mode shapes. At the Pennsylvania State University, the Acoustical Society of America student chapter acquired funds to build an ESPI for classroom and outreach use. The design of the ESPI was based on previously published work using equipment purchased for less than $5000. To approach this project, students were split into two groups where one developed a MATLAB application to collect and process images while the other arranged the optical components of the ESPI. To test the system, interferometry was performed on a banjo head which matched mode shapes found using a scanning Laser Doppler Vibrometer (LDV). Future work includes adapting our ESPI system to obtain images in real-time, developing educational demos involving the ESPI, and further refining the MATLAB application. This presentation provides a model for a multi-disciplinary project that could be implemented at the undergraduate or graduate level.

No abstract

No abstract