Toxic dumpsites on the seafloor are causing increasing environmental concern, in particular around Europe. But a major obstacle toward realistic and quantitative risk evaluation at known dumpsites is the low efficiency of existing technology in determining the extension and location of objects in unconsolidated sediments. The EC project SITAR developed innovative solutions to this challenge, in particular through the development of acoustic methods and instrumentation for imaging waste barrels/containers of small dimensions. The study and experimental verification of ?Multiple-Aspect Scattering? techniques were achieved through scaled experiments in our tank facilities, using real types of seabed representative of European shores and scaled targets. High-frequency (238 kHz) bistatic scattering is investigated with a 5-degree of freedom robotics system, enabling the positioning of the source and hydrophones at different distances from each other, and at different depths in the water column. This set-up is a scaled-down version of the SITAR sea trials performed in September/October 2003 in the Stockholm Archipelago, except that it offers a totally controlled laboratory environment. We measured the acoustic scattering of the targets and the background (silt) seabed, imaged with a highly directional beam at 45° grazing angle. These measurements were taken as a function of the bistatic angle (in-plane, 10° and 20° away) and the scattering angle (22° to 73°). The results presented here focus on the variations of target scattering with target orientation (end-on, diagonal, broadside-on, as well as vertical) and target type (e.g. solid vs. fluid-filled, plain vs. ribbed). The relative orientation of the targets can be deduced from the variations with scattering angle. Their shape and content yield distinct acoustic characteristics when viewed at different bistatic angles. These results are discussed in the wider framework of other full-scale trials and the SITAR sea trials.
|Publication status||Published - Jun 2007|
|Event||Underwater Acoustics Measurements 2007 - Heraklion, Crete|
Duration: 1 Jun 2007 → …
|Conference||Underwater Acoustics Measurements 2007|
|Period||1/06/07 → …|