Sidescan high-frequency (HF) sonar (i.e., with frequencies higher than 100 kHz) is ideally suited for providing high-resolution images of the seafloor. However, since sound does not penetrate into the sediment at these frequencies, such systems cannot be used for the detection of buried objects, such as naval mines, improvised explosive devices (IEDs), and unexploded ordinance (UXO). Sidescan low-frequency (LF) sonar is a promising technology for the detection of objects buried in soft seafloor sediment. Acoustic energy is attenuated less by the sediment at lower frequencies and can therefore penetrate deeper, facilitating the detection of buried objects. Furthermore, a side-looking configuration yields a much higher area coverage rate compared to downward-looking systems (e.g., the BOSS system [1]), thus enabling efficient surveys. In practice there are two fundamental issues with sidescan LF sonar. The resolution of conventional sidescan sonar is poor at low frequencies due to the lower directivity of the beams. Moreover, in addition to the targets of interest, many clutter contacts are also observed, including other buried objects (e.g., boulders) and geological features below the mud (e.g., sand ripples). Thus, a means of classification is necessary to distinguish between targets and clutter and to suppress the false alarms. Synthetic aperture sonar (SAS) processing is essential for attaining adequate image resolution and for facilitating object classification in order to realise an operational capacity.
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