简介：

简介：Twoassumptionsaretypicallymadewhenradarechosignalsfromprecipitationareanalyzedtodeterminethemicro-physicalparametersofraindrops:(1)theraindropsareassumedtobespherical;(2)multiplescatteringeffectsareignored.Radarcrosssections(RCS)areusuallycalculatedusingRayleigh'sscatteringequationwiththesimpleadditionmethodintheradarmeteorologicalequation.Weinvestigatetheextenttowhichconsiderationoftheeffectsofmultiplescatteringandofthenon-sphericalshapeswithinactualraindropswarmswouldresultinRCSvaluessignificantlydifferentfromthoseobtainedbyconventionalanalyticalmethods.First,weestablishsphericalandnon-sphericalraindropmodels,withGamma,JD,JT,andMPsizedistributions,respectively.WethenuseXFDTDsoftwaretocalculatetheradarcrosssectionsoftheaboveraindropmodelsattheS,C,XandKuradarbands.OurXFDTDresultsarethencomparedtoRCSvaluescalculatedbytheRayleighapproximationwithsimpleadditionmethods.Wefindthat:(1)RCSvaluescalculatedusingmultiplescatteringXFDTDsoftwarediffersignificantlyfromthosecalculatedbythesimpleadditionmethodatthesamebandforthesamemodel.Inparticular,forthesphericalraindropmodels,therelativedifferencesinRCSvaluesbetweenthemethodsrangefromamaximumof89.649%toaminimumof43.701%;forthenon-sphericalraindropmodels,therelativedifferencesrangefromamaximumof85.868%toaminimumof11.875%.(2)OurmultiplescatteringXFDTDresults,comparedtothoseobtainedfromtheRayleighformula,againdifferatallfoursizedistributions,byrelativeerrorsof169.522%,37.176%,216.455%,and63.428%,respectively.Whennonsphericaleffectsareconsidered,differencesinRCSvaluesbetweenourXFDTDcalculationsandRayleighcalculationsaresmaller;attheabovefoursizedistributionstherelativeerrorsare0.213%,0.171%,7.683%,and44.514%,respectively.RCSvaluescomputedbyconsideringmultiplescatteringandnon-sphericalparticleshapesarelargerthanRayleighRCS