Digging up the dirt on buried waste
The objective of the SITAR project has been pursued through the development of acoustic methods and oceanographic instrumentation for the imaging of water containers of small dimension buried in unconsolidated sea sediments. This effort was based on the development of a new type of sonar system, using the principle of the bottom-penetrating parametric sonar, but with the imaging capabilities of the traditional side-scan sonar. Parametric sonars are instruments capable of transmitting acoustic signals in the water with a very narrow beam and almost no sidelobes. Parametric sonars for sub-bottom profiling are being used to achieve higher spatial resolution than conventional sub-bottom profilers. Parametric side scan sonars (PSSS) comprise a new evolution in this technology. In PSSS high frequency primary signals are used to produce a conventional side scan image of the seabed, while the parametrically generated difference frequency (low frequency) is used for penetration into the sediments in the same area. Depth information is acquired after the interferometric processing of the signals received by two receiver arrays. The received signals are processed by specialized software developed in the context of the project, providing a 3-D synthetic aperture sonar-processing package. PSSS will assist the efforts to assess the threats posed by toxic dumpsites and improve the surveying and detection of buried or partly buried objects such as waste, sources of pollution, mines etc. In this way, monitoring and decision-making will be facilitated with beneficial environmental and economic consequences for marine life and human related activities.