外文翻译--ccd图像

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1、附录附录1翻译部分RawCCDimagesareexceptionalbutnotperfect.Duetothedigitalnatureofthedatamanyoftheimperfectionscanbecompensatedfororcalibratedoutofthefinalimagethroughdigitalimageprocessing.CompositionofaRawCCDImage.ArawCCDimageconsistsofthefollowingsignalcomponents:IMAGESIGNAL-Th

2、esignalfromthesource.Electronsaregeneratedfromtheactualsourcephotons.BIASSIGNAL-InitialsignalalreadyontheCCDbeforetheexposureistaken.ThissignalisduetobiasingtheCCDoffsetslightlyabovezeroA/Dcounts(ADU).THERMALSIGNAL-Signal(DarkCurrentthermalelectrons)duetothethermalactivi

3、tyofthesemiconductor.ThermalsignalisreducedbycoolingoftheCCDtolowtemperature.SourcesofNoiseCCDimagesaresusceptibletothefollowingsourcesofnoise:PHOTONNOISE-Randomfluctuationsinthephotonsignalofthesource.Therateatwhichphotonsarereceivedisnotconstant.THERMALNOISE-Statistica

4、lfluctuationsinthegenerationofThermalsignal.Therateatwhichelectronsareproducedinthesemiconductorsubstrateduetothermaleffectsisnotconstant.READOUTNOISE-Errorsinreadingthesignal;generallydominatedbytheon-chipamplifier.QUANTIZATIONNOISE-ErrorsintroducedintheA/Dconversionpro

5、cess.SENSITIVITYVARIATION-SensitivityvariationsfromphotositetophotositeontheCCDdetectororacrossthedetector.ModernCCD'sareuniformtobetterthan1%betweenneighboringphotositesanduniformtobetterthan10%acrosstheentiresurface.NoiseCorrectionsREDUCINGNOISE-ReadoutNoiseandQuantiza

6、tionNoisearelimitedbytheconstructionoftheCCDcameraandcannotbeimproveduponbytheuser.ThermalNoise,however,canbereducedbycoolingoftheCCD(temperatureregulation).TheSensitivityVariationscanberemovedbyproperflatfielding.CORRECTINGFORTHEBIASANDTHERMALSIGNALS-TheBiasandThermalsi

7、gnalscanbesubtractedoutfromtheRawImagebytakingwhatiscalledaDarkExposure.ThedarkexposureisameasureoftheBiasSignalandThermalSignalandmaysimplybesubtractedfromtheRawImage.FLATFIELDING-Arecordofthephotositetophotositesensitivityvariationscanbeobtainedbytakinganexposureofauni

8、formlylit'flatfield".ThesevariationscanthenbedividedoutoftheRawImagetoproduceanimageessentiallyfreefrom