FPGA Data Processing Platforms for Photoacoustic Airborne Sonar

Traditional sonar can be used to produce underwater images with high fidelity, depth, and resolution. However, it suffers from one major drawback: the sonar module must be in contact with the water surface. This means the underwater imaging process is limited by the size, maneuverability, and cost of the carrying ships. This makes large area coverage very expensive and more invasive to local ecosystems, among other drawbacks. A much more scalable solution would be to create an airborne platform that can image underwater (i.e on a drone); however, all sensing methods in use today suffer from physical limitations that prevent their usage for imaging across the air-water boundary with sufficient range and resolution. A new imaging modality shows promise: by using a pulsed laser focused on the water surface to generate acoustic waves via the photoacoustic effect, it is possible to collect strong acoustic signals and thereby make sonar possible through the air-water boundary. Acoustic refraction from a non-planar surface in hydrodynamic conditions can be addressed with an auxiliary sensing system that employs traditional sonar to map the water surface. However, there are no off-the-shelf solutions for robust detection of either of these acoustic signals at the required spatial and temporal resolution. Instead, custom systems must be designed to reach key sensing goals. This research thesis describes the design, creation, and characterization of two hardware back-ends that can control and interpret two custom-designed sensor arrays and deliver the data robustly to downstream reconstruction software.