?url_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rft.relation=http%3A%2F%2Fwww.eledia.org%2Fstudents-reports%2F363%2F&rft.title=A+Qualitative+Two-Step+Inversion+Approach+for+the+Reconstruction+of+Subsurface+Defects&rft.creator=Donelli%2C+Massimo&rft.creator=Benedetti%2C+Manuel&rft.creator=Lesselier%2C+D.&rft.creator=Massa%2C+Andrea&rft.subject=TU+Technical+Reports+and+Publications&rft.description=The+detection+of+subsurface+objects+such+as+landmine+or+archaeological+find%2C+the+location+of+sedimentary+layer+for+geological+inspections%2C+or+the+identification+of+cracks+and+voids+in+host+structures+are+some+examples+of+applications+where+the+reconstruction+of+the+position+and+the+shape+of+unknown+targets+embedded+in+inaccessible+regions+is+required.+In+this+framework%2C+the+imaging+methods+based+on+electromagnetic+inverse+scattering+theory+can+play+a+key+role+%5B1%5D.+As+a+matter+of+fact%2C+the+electromagnetic+and+geometric+properties+of+the+region+under+test+can+be+quantitatively+reconstructed+starting+from+the+observation+of+the+scattered+field.+Unfortunately%2C+the+problem+at+hand+presents+several+drawbacks+such+as+non-linearity+and+ill-posedness+that+need+to+be+taken+into+account+especially+when+dealing+with+complex+scenarios.+However%2C+a+considerable+amount+of+a-priori+information+is+generally+available+in+nondestructive+testing+and+evaluation+(NDT%2FNDE)+applications%2C+since+the+crack+to+be+reconstructed+is+located+in+a+known+host+medium+%5B2%5D.+Such+a+peculiarity+can+be+profitably+exploited+in+order+to+cope+with+the+lack+of+information+characterizing+the+inverse+problem.+In+such+a+framework%2C+microwave+methodologies+based+on+the+use+of+heuristic+optimizers+and+on+the+exploitation+of+the+a-priori+information+have+been+effectively+used+for+the+detection+of+a+crack+in+a+known+host+structure+%5B3%5D+or+when+dealing+with+more+complex+and+realistic+scenarios+characterized+by+multiple+defects+%5B4%5D.+The+proposed+approaches+demonstrate+their+feasibility+and+effectiveness+in+providing+a+coarse+estimation+of+the+targets+in+a+qualitative+fashion%2C+but+they+are+not+suitable+for+the+retrieval+of+complex+shapes.+In+this+work%2C+a+two-step+procedure+successfully+adopted+for+NDT%2FNDE+problems+%5B5%5D+has+been+employed+for+the+qualitative+reconstruction+of+complex+subsurface+targets.+In+particular%2C+at+the+first+step+the+target+is+localized+and+its+shape+is+roughly+estimated+starting+from+the+knowledge+of+the+scattered+field.+Then%2C+the+second+step+is+aimed+at+refining+the+contour+of+the+target+by+means+of+a+shape+optimization+technique+characterized+by+the+evolution+of+a+level+set+function+%5B6%5D.&rft.date=2011-01&rft.type=Technical+Report&rft.type=NonPeerReviewed&rft.format=application%2Fpdf&rft.language=en&rft.identifier=http%3A%2F%2Fwww.eledia.org%2Fstudents-reports%2F363%2F1%2FDISI-11-185.C182.pdf&rft.identifier=++Donelli%2C+Massimo+and+Benedetti%2C+Manuel+and+Lesselier%2C+D.+and+Massa%2C+Andrea++(2011)+A+Qualitative+Two-Step+Inversion+Approach+for+the+Reconstruction+of+Subsurface+Defects.++%5BTechnical+Report%5D+++++