Towards a Seafloor Passive Acoustic Geodetic Marker for Underwater Surveying

Deploying and relocating reference points are a core capability in terrestrial surveying. These references are useful for monitoring environmental changes over time and co-registering multiple surveys conducted at different times. Similar approaches for monitoring changes over time have been developed for underwater surveys. These references are especially critical in the GPS-denied deep ocean and can take different forms dependent upon sensing capabilities. Terrain-based alignment approaches and active acoustic beacons have been researched and demonstrated for acoustic surveying conducted with multibeam echosounders. However, these approaches are either limited in their operational environments, expensive to deploy, or only useful for short periods of time. As such, the development of a passive acoustic geodetic marker provides promise for improved change detection in underwater surveying. The proposed passive acoustic geodetic marker is a cross-shaped marker made up of sealed air volumes designed to be easily detectable with a 400kHz MBES, deployable for long periods of time at low cost, and have a low environmental impact. By deploying proposed marker designs in known locations around a site prior to an acoustic survey, they can serve as reference points for long-term monitoring or alignment across multiple surveys of the same area.