激光测距-外文翻译

LaserrangefinderAlongrangelaserrangefinderiscapableofmeasuringdistanceupto20km;mountedonatripodwithanangularmount.Theresultingsystemalsoprovidesazimuthandelevationmeasurements.Alaserrangefinderisadevicewhichusesalaserbeamtodeterminethedistancetoanobject.Themostcommonformoflaserrangefinderoperatesonthetimeofflightprinciplebysendingalaserpulseinanarrowbeamtowardstheobjectandmeasuringthetimetakenbythepulsetobereflectedoffthetargetandreturnedtothesender.Duetothehighspeedoflight,thistechniqueisnotappropriateforhighprecisionsub-millimetermeasurements,wheretriangulationandothertechniquesareoftenused.PulseThepulsemaybecodedtoreducethechancethattherangefindercanbejammed.ItispossibletouseDopplereffecttechniquestojudgewhethertheobjectismovingtowardsorawayfromtherangefinder,andifsohowfast.PrecisionTheprecisionoftheinstrumentisdeterminedbytheriseorfalltimeofthelaserpulseandthespeedofthereceiver.Onethatusesverysharplaserpulsesandhasaveryfastdetectorcanrangeanobjecttowithinafewmillimeters.RangeDespitethebeambeingnarrow,itwilleventuallyspreadoverlongdistancesduetothedivergenceofthelaserbeam,aswellasduetoscintillationandbeamwandereffects,causedbythepresenceofairbubblesintheairactingaslensesranginginsizefrommicroscopictoroughlyhalftheheightofthelaserbeam'spathabovetheearth.Theseatmosphericdistortionscoupledwiththedivergenceofthelaseritselfandwithtransversewindsthatservetopushtheatmosphericheatbubbleslaterallymaycombinetomakeitdifficulttogetanaccuratereadingofthedistanceofanobject,say,beneathsometreesorbehindbushes,orevenoverlongdistancesofmorethan1kminopenandunobscureddesertterrain.Someofthelaserlightmightreflectoffleavesorbrancheswhicharecloserthantheobject,givinganearlyreturnandareadingwhichistoolow.Alternatively,overdistanceslongerthan1200ft(365m),thetarget,ifinproximitytotheearth,maysimplyvanishintoamirage,causedbytemperaturegradientsintheairinproximitytotheheatedsurfacebendingthelaserlight.Alltheseeffectshavetobetakenintoaccount.CalculationThedistancebetweenpointAandBisgivenbyD=ct/2wherecisthespeedoflightintheatmosphereandtistheamountoftimefortheround-tripbetweenAandB.whereisthedelaywhichmadebythelighttravelingandistheangularfrequencyofopticalmodulation.ThensubstitutethevaluesintheequationD=ct/2,D=1/2ct=1/2c·φ/ω=c/(4πf)(Nπ+Δφ)=c/4f(N+ΔN)=U(N+)inthisequation,Ustandsfortheunitlength.Δφstandsforthedelaypartwhichdoesnotfulfillπ.ΔNstandsthedecimalvalue.DiscriminationSomeinstrumentsareabletodeterminemultiplereturns,asabove.Theseinstrumentsusewaveform-resolvingdetectors,whichmeanstheydetecttheamountoflightreturnedoveracertaintime,usuallyveryshort.Thewaveformfromalaserpulsethathitsatreeandthenthegroundwouldhavetwopeaks.Thefirstpeakwouldbethedistancetothetree,andthesecondwouldbethedistancetotheground.Usingwavefrontsensing,itispossibletodetermineboththeclosestandthefarthestobjectatagivenpoint.Thismakesitpossibleforaircraft-mountedinstrumentstoseethroughdensecanopies[clarificationneededPleaseexplainhowlasersseethroughcanopies]andothersemi-reflectivesurfacesuchastheocean,leadingtomanyapplicationsforairborneinstrumentssuchas:1.Creatingbareearthtopographicmaps-removingalltrees2.Creatingvegetationthicknessmaps3.Bathymetry(measuringtopographyundertheocean)4.ForestfirehazardTechnologiesTimeofflight-thismeasuresthetimetakenforalightpulsetotraveltothetargetandback.Withthespeedoflightknown,andanaccuratemeasurementofthetimetaken,thedistancecanbecalculated.Manypulsesarefiredsequentiallyandtheaverageresponseismostcommonlyused.Thistechniquerequiresveryaccuratesub-nanosecondtimingcircuitry.Multiplefrequencyphase-shift-thismeasuresthephaseshiftofmultiplefrequenciesonreflectionthensolvessomesimultaneousequationstogiveafinalmeasure.Interferometry-themostaccurateandmostusefultechniqueformeasuringchangesindistanceratherthanabsolutedistances.ApplicationsMilitaryAnAmericansoldierwithaGVS-5laserrangefinder.ADutchISAFsniperteamdisplayingtheirAccuracyInternationalAWSM.338LapuaMagnumrifleandLeica/VectronixVECTORIVlaserrangefinderbinoculars.Rangefindersprovideanexactdistancetotargetslocatedbeyondthedistanceofpoint-blankshootingtosnipersandartillery.Theycanalsobeusedformilitaryreconciliationandengineering.Handheldmilitaryrangefindersoperateatrangesof2kmupto25kmandarecombinedwithbinocularsormonoculars.Whentherangefinderisequippedwithadigitalmagneticcompass(DMC)andinclinometeritiscapableofprovidingmagneticazimuth,inclination,andheight(length)oftargets.Somerangefinderscanalsomeasureatarget'sspeedinrelationtotheobserver.Somerangefindershavecableorwirelessinterfacestoenablethemtotransfertheirmeasurement(s)datatootherequipmentlikefirecontrolcomputers.Somemodelsalsoofferthepossibilitytouseadd-onnightvisionmodules.Mosthandheldrangefindersusestandardorrechargeablebatteries.Themorepowerfulmodelsofrangefindersmeasuredistanceupto25kmandarenormallyinstalledeitheronatripodordirectlyonavehicleorgunplatform.Inthelattercasetherangefindermoduleisintegratedwithon-boardthermal,nightvisionanddaytimeobservationequipment.Themostadvancedmilitaryrangefinderscanbeintegratedwithcompu