Low-Frequency Synthetic Aperture Sonar System for the Detection of Objects Buried in Mud

Naval mines, underwater improvised explosive devices (UW-IEDs), and underwater unexploded ordnance (UW-UXO) are concerns for harbour security. In conditions without burial, existing commercial systems, such as the REMUS unmanned underwater vehicle equipped with a (very) high frequency side scan sonar (900/1800 kHz), may be deployed for detection and classification. However, it is common that bottom conditions in harbours are such that objects may become covered by mud and sometimes by sand. In the case of burial, a high-frequency sonar system cannot detect objects due to its limited penetration depth. To counter the threat of buried objects in mud, a low frequency (LF: 4-26 kHz) side looking synthetic aperture sonar (SAS) demonstrator system has been developed. This type of system has a bottom penetrating detection potential, combined with a considerable swath. Even with a limited speed of advance (e.g. 2-4 kts) an operationally relevant area coverage rate can be obtained. The system performance has been evaluated in trials in the Haringvliet, an estuary in the Netherlands, conducted in close collaboration with the Royal Netherlands Navy (RNLN). In these trials, it is confirmed that the LF SAS system is capable of detecting buried objects that are not detected by REMUS. Furthermore, buried objects are detected at ranges up to four times the water depth, indicating that a relevant area coverage rate can be achieved