简介：AnewFFTalgorithmhasbeendeduced,whichiscalledthebase-6FFTalgorithm.TheamountforcalculatingtheDFTofcomplexsequenceofN=2rbythebase-6FFTalgorithmisMr(N)=14/3*Nlog6N-4N+4formultiplicationoperationofrealnumberandAr(N)=23/3*Nlog6N-2N+2foradditionoperationofrealnumber.TheamountforcalculatingtheDFTofrealsequenceisahalfofitwiththecomplexsequence.

简介：Thereexistthreetypesofconvolutionformulaefortheefficientevaluationofgravityfieldconvolutionintegrals,i.e.,theplanar2Dconvolution,thespherical2Dconvolutionandthespherical1Dconvolution.Thelargestdrawbackofboththeplanarandthespherical2DFFTmethodsisthat,duetotheapproximationsinthekernelfunction,onlyinexactresultscanbeachieved.Apparently,thereasonisthemeridianconvergenceathigherlatitudes.Asthemeridiansconverge,theΔφ,Δλblocksdonotformarectangulargrid,asisassumedin2DFFTmethods.Itshouldbepointedoutthatthemeridianconvergencenotonlyleadstoanapproximationerrorinthekernelfunction,butalsocausesanapproximationerrorduringtheimplementationof2DFFTincomputer.Inordertomeettheincreasingneedforprecisedeterminationoftheverticaldeflections,thispaperderivesamorepreciseplanar2DFFTformulaforthecomputationoftheverticaldeflections.Afterhavingmadeadetailedcomparisonbetweentheplanarandthespherical2DFFTformulae,wefindoutthemainsourceoferrorscausingthelossinaccuracybyapplyingtheconventionalspherical2DFFTmethod.Andthen,amodifiedspherical2DFFTformulaforthecomputationoftheverticaldeflectionsisdevelopedinthispaper.Aseriesofnumericaltestshavebeencarriedouttoillustratetheimprovementmadeupontheoldspherical2DFFT.Thesecondpartofthispaperistodiscusstheinfluencesofthesphericalharmonicreferencefield,thelimitedcapsize,andthesingularintegralonthecomputationoftheverticaldeflections.TheresultsoftheverticaldeflectionsoverChinabyapplyingthespherical1DFFTformulawithdifferentintegrationradiihavebeencomparedtotheastro-observedverticaldeflectionsintheSouthChinaSeatoobtainasetofoptimumdeflectioncomputationparameters.

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简介：介绍了一种实数快速傅里叶变换(FFT)的设计原理及实现方法,利用输入序列的对称性,将2N点的实数FFT计算转化为N点复数FFT计算,然后将FFT的N点复数输出序列进行适当的运算组合,获得原实数输入的2N点FFT复数输出序列,使FFT的运算量减少了近一半,很大程度上减少了系统的运算时间,解决了信号处理系统要求实时处理与傅里叶变换运算量大之间的矛盾.同时,给出了在TMS320VC5402DSP上实现实数FFT的软件设计,并比较了执行16,32,64,128,256,512,1024点实数FFT程序代码与相同点数复数FFT的程序代码运行时间.经过实验验证,各项指标均达到了设计要求.

简介：图像压缩所要解决的问题是如何最大限度地压缩图像数据,并保证利用这些数据所重建的图像是用户能够接受的.本文分析了微光图像特征,在此基础上利用傅立叶变换(FFT)对微光夜视图像进行了压缩编码研究,并阐述了FFT的基本原理,得到了不同压缩比下的压缩结果.

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