Synthetic aperture sonar (SAS) is a form of sonar technology that is designed to make up for the shortcomings of traditional side scan sonar, which provides decreasing image quality and resolution as the distance from the sensor’s transducer array increases. Increasing the quality of the image at a particular distance for a side scan sonar would require a larger array, which will eventually be limited by the size and capability of the host vehicle.
Synthetic aperture sonar shares similar operating principles with synthetic aperture radar, using the forward motion of the platform it is mounted on to create an artificially larger aperture. Unlike traditional sonar scanning, which sends out one ping at a time and waits for the return echo before sending out another one, SAS sends out multiple pulses, making multiple measurements at each location, and combines the returned signals. The overlap results in highly detailed images with resolution that can exceed that of side scan sonar by an order of magnitude.
SAS for Unmanned Systems
SAS systems may be mounted on UUVs (unmanned underwater vehicles) such as ROVs (remotely operated vehicles) and AUVs (autonomous underwater vehicles), as well as USVs (uncrewed surface vessels) and towfish.
As the increased number of pings draws more power and the data processing is computationally intense, synthetic aperture sonars may be better suited to larger AUVs and other vehicles with less restrictive SWaP (size, weight and power) budgets. Errors in the measurements of SAS systems can be reduced by fusing with data from an INS (inertial navigation system), so vehicles with high-accuracy inertial sensors on board are also well-suited to the technology.
Synthetic aperture sonar is used for a range of military and civilian applications, including bathymetry, mapping, mine counter-measures (MCM), underwater archaeology, and environmental research.