Synthetic Aperture Sonar Nadir Gap Coverage with Centimetric Resolution

Synthetic aperture sonar (SAS) is an acoustic imaging technique capable of providing constant resolution over a wide swath. Similar to sidescan sonar, SAS has a coverage gap directly below the system known as the nadir gap. Developing nadir gap coverage technologies for SAS is challenging because it is difficult to match its altitude and resolution capabilities. In this paper, we introduce a unique gap reduction technique that combines a short-range SAS designed to reduce the nadir gap, with an auxiliary sensor to provide complete nadir gap coverage. Two different auxiliary sensors are investigated: a 3D laser profiler and a multibeam echosounder. Results indicate that all three gap fill solutions are capable of providing high (centimetric) resolution for a high speed towed SAS system operating at 10 m altitude. When combined, the sensors can provide full swath coverage that results in a 33% increase in area coverage rate.