Detection and classification ofburiedtargets and sub-bottom geoacoustic inversionwith anAUV carriedlow frequencyacoustic sourceand atowedarray

An innovative bottomacoustic surveytechnique involving an AutonomousUnderwaterVehicle(AUV) is presented. Inthistechnique, theAUV carries alowfrequency broadbandacoustic sourceanda towedacoustic arrayand operates close totheseabed. Theproposed technique hasgreat potential toimprove thecapability ofdetecting andclassifying buried orhalfburied targets, andproviding amorereliable sub- bottomgeoacoustic inversion methodovera largeareafor geological andgeophysical surveys. Specifically, since thesource andthereceiving arrayareveryclose totheseafloor, avariety of surface andreflected waveswithgoodSNR isexpected tobe received bythehydrophone array. Allofthese waveshavetheir own uniqueacoustic characteristics, whichcanbeusedfor seafloor andsub-bottom geoacoustic inversion. Results from numerical simulations basedonsynthetic datawill bepresented todemonstrate howthegeometric andphysical properties ofthe seafloor, sub-bottom, andburied targets influence thereceived echoes ineither thetimedomain, thefrequency domain, orboth. Thesimulation results will bediscussed.. I. INTRODUCTION An innovative acoustic survey technique involving an Autonomous Underwater Vehicle (AUV)ispresented inthis paper. Inthis technique, theAUV carries alowfrequency broadband acoustic source andatowedacoustic array, and operates close totheseabed (preferably within anacoustic wavelength) Theproposed technique hasagreat potential to improve ourcapability ofdetecting andclassifying buried or half buried targets, andproviding amorereliable sub-bottom geoacoustic inversion method overalarge areaforgeological andgeophysical surveys. Sincetheacoustic transmitter is mounted ontheAUV,thepositions ofthehydrophones inthe towedarray relative totheacoustic source canbeprecisely determined. Suchaconfiguration canimprove beamforming operation andcanalso beusedforasynthetic aperture sonar operation. Inaddition, theAUV canbeeasily deployed and operated toflywithin 1-2m abovetheseafloor sothat even withamodest source level, thesignal-to-noise ratio (SNR)of thereceived echoes fromtheseafloor, theinterfaces ofthe sub-bottom layers, andtheirregular andburied targets canbe