Scatteringattenuationinshortwavelengthshaslongbeeninterestingtogeophysicists.Ultrasoniccodawaves,observedasthetailportionofultrasonicwavetrainsinlaboratoryultrasonicmeasurements,areimportantforsuchstudieswhereultrasonicwavesinteractwithsmallscalerandomheterogeneitiesonascaleofmicrometers,butoftenignoredasnoisesbecauseofthecontaminationofboundaryreflectionsfromthesideendsofasamplecore.Numericalsimulationswithaccurateabsorbingboundarycanprovideinsightintotheeffectofboundaryreflectionsoncodawavesinlaboratoryexperiments.Thesimulationofwavepropagationindigitalandheterogeneousporouscoresreallychallengesnumericaltechniquesbydigitalimageofporoelasticproperties,numericaldispersionathighfrequencyandstrongheterogeneity,andaccurateabsorbingboundaryschemesatgrazingincidence.Toovercomethesedifficulties,wepresentastaggered-gridhigh-orderfinite-difference(FD)methodofBiot’sporoelasticequations,withanarbitraryeven-order(2L)accuracytosimulateultrasonicwavepropagationindigitalporouscoreswithstrongheterogeneity.Anunsplitconvolutionalperfectlymatchedlayer(CPML)absorbingboundary,whichimprovesconventionalPMLmethodsatgrazingincidencewithlessmemoryandbettercomputationalefficiency,isemployedinthesimulationtoinvestigatetheinfluenceofboundaryreflectionsonultrasoniccodawaves.Numericalexperimentswithsaturatedporoelasticmediademonstratethatthe2LFDschemewiththeCPMLforultrasonicwavepropagationsignificantlyimprovesstabilityconditionsatstrongheterogeneityandabsorbingperformanceatgrazingincidence.TheboundaryreflectionsfromtheartificialboundarysurroundingthedigitalcoredecayfastwiththeincreaseofCPMLthicknesses,almostdisappearingattheCPMLthicknessof15grids.ComparisonsoftheresultingultrasoniccodaQscvaluesbetweenthenumericalandexperimentalultrasonicSwaveformsforacylindricalrocksampledemonstratethatthe
