《信息工程专业英语》课件第8章

Unit8Radar8.1Text8.2ReadingMaterials

8.1Text

Radar

Radarisanobjectdetectionsystemwhichusesradiowavestodeterminetherange,altitude,direction,orspeedofobjects.Itcanbeusedtodetectaircraft,ships,spacecraft,guidedmissiles,motorvehicles,weatherformations,andterrain.Theradardishantennatransmitspulsesofradiowavesormicrowaveswhichbounceoffanyobjectintheirpath.Theobjectreturnsatinypartofthewave'senergytoadishorantennawhichisusuallylocatedatthesamesiteasthetransmitter.

RadarwassecretlydevelopedbyseveralnationsbeforeandduringWorldWarII.ThetermRADARwascoinedin1940bytheUnitedStatesNavyasanacronymforRadioDetectionandRanging.ThetermradarhassinceenteredEnglishandotherlanguagesasthecommonnounradar,losingallcapitalization.

Themodernusesofradararehighlydiverse,includingairtrafficcontrol,radarastronomy,air-defensesystems,antimissilesystems;marineradarstolocatelandmarksandotherships;aircraftanticollisionsystems;oceansurveillancesystems,outerspacesurveillanceandrendezvoussystems;meteorologicalprecipitationmonitoring;altimetryandflightcontrolsystems;guidedmissiletargetlocatingsystems;andground-penetratingradarforgeologicalobservations.Hightechradarsystemsareassociatedwithdigitalsignalprocessingandarecapableofextractingusefulinformationfromveryhighnoiselevels.

Othersystemssimilartoradarmakeuseofotherpartsoftheelectromagneticspectrum.Oneexampleis“lidar”,whichusesvisiblelightfromlasersratherthanradiowaves.

Theinformationprovidedbyradarincludesthebearingandrange(andthereforeposition)oftheobjectfromtheradarscanner.Itisthususedinmanydifferentfieldswheretheneedforsuchpositioningiscrucial.Thefirstuseofradarwasformilitarypurposes:tolocateair,groundandseatargets.RadarformilitaryisshowninFig8.1.Thisevolvedinthecivilianfieldintoapplicationsforaircraft,ships,androads.

Inaviation,aircraftareequippedwithradardevicesthatwarnofobstaclesinorapproachingtheirpathandgiveaccuratealtitudereadings.Thefirstcommercialdevicefittedtoaircraftwasa1938BellLabunitonsomeUnitedAirLinesaircraft.Suchaircraftcanlandinfogatairportsequippedwithradar-assistedground-controlledapproachsystemsinwhichtheplane'sflightisobservedonradarscreenswhileoperatorsradiolandingdirectionstothepilot.

Fig8.1Radarformilitary

Marineradarsareusedtomeasurethebearinganddistanceofshipstopreventcollisionwithotherships,tonavigate,andtofixtheirpositionatseawhenwithinrangeofshoreorotherfixedreferencessuchasislands,buoys,andlightships.Inportorinharbour,vesseltrafficserviceradarsystemsareusedtomonitorandregulateshipmovementsinbusywaters.Policeforcesuseradargunstomonitorvehiclespeedsontheroads.

Meteorologistsuseradartomonitorprecipitation.Ithasbecometheprimarytoolforshort-termweatherforecastingandwatchingforsevereweathersuchasthunderstorms,tornadoes,winterstorms,precipitationtypes,etc.Geologistsusespecialisedground-penetratingradarstomapthecompositionofEarth’scrust.

Technicalwordsandphrases

altitude n.高度

missile

n.导弹adj.导弹的；用以发射导弹的

vehicle

n.工具；运载工具；传播媒介；媒介物

terrain

n.地形，地势；领域

antenna

n.天线

capitalization

n.用大写

marine

adj.船舶的

landmark

n.陆标，地标

collision

n.冲突

rendezvous

n.交会，对接

meteorological

adj.气象的；气象学的

precipitation

n.冰雹

monitoring

n.监控

altimetry

n.测高法，高度测量术

penetrate

vt.渗透；穿透

geological

adj.地质的，地质学的

lidar

n.激光雷达；激光定位器

lasers

n.激光

bearing n.方位

crucial

adj.重要的；决定性的

civilian adj.民用的；百姓的，平民的

aviation

n.航空；飞行术；飞机制造业

navigate

vt.驾驶，操纵；使通过；航行于

buoy

n.浮标；浮筒；航标

port

n.港口，口岸

harbour n.海港

tornadoe n.龙卷风

crust

n.地壳

radiowaves

无线电波

guidedmissiles

精确制导导弹

motorvehicles

摩托化运载工具

bounceoff

反射

airtrafficcontrol 空中交通管制

antimissilesystems

反导系统

marineradars

船舶雷达

busywaters 激流

aircraftanticollisionsystems

空中防撞击系统

meteorological

precipitationmonitoring

冰雹灾害预警

compositionofEarth'scrust

地壳合成图

8.1.1Exercises

1.PutthePhrasesintoEnglish

(1)抛物面天线；

(2)无线侦查；

(3)空中交通管制；

(4)雷达天文学；

(5)反导系统；

(6)电磁频谱；

(7)民用领域；

(8)恶劣气象；

(9)短期预报。

2.PutthePhrasesintoChinese

(1)radiowaves;

(2)airtrafficcontrol;

(3)oceansurveillancesystems;

(4)air-defensesystems;

(5)militarypurposes;

(6)compositionofEarth’scrust.

3.Translation

(1)Theobjectreturnsatinypartofthewave’senergytoadishorantennawhichisusuallylocatedatthesamesiteasthetransmitter.

(2)ThetermRADARwascoinedin1940bytheUnitedStatesNavyasanacronymforRadioDetectionandRanging.

(3)Hightechradarsystemsareassociatedwithdigitalsignalprocessingandarecapableofextractingusefulinformationfromveryhighnoiselevels.

(4)Inaviation,aircraftareequippedwithradardevicesthatwarnofobstaclesinorapproachingtheirpathandgiveaccuratealtitudereadings.

(5)Suchaircraftcanlandinfogatairportsequippedwithradar-assistedground-controlledapproachsystemsinwhichtheplane‘sflightisobservedonradarscreenswhileoperatorsradiolandingdirectionstothepilot.

(6)Inportorinharbour,vesseltrafficserviceradarsystemsareusedtomonitorandregulateshipmovementsinbusywaters.

8.1.2参考译文

雷达是通过运用无线电波来确定目标物体大小、高度、方向和速度的侦查系统。可用于侦测飞行器、舰艇、航天器、导弹、机动车辆、天气以及地形。由雷达的碟形天线发射出的无线电波和微波脉冲，在其传播线路上，如果遇到障碍物即产生反射现象。障碍物将微波的一小部分能量反射至和发射器位于同一站点的碟形天线。

很多国家在二战前及二战期间秘密发展了雷达。术语“雷达”一词于1940年被美国海军作为无线电探测和测距的英文缩写而确立下来。自从“雷达”这一名词进入了英语及其他语言体系后，就失去了大小写。

如今雷达的应用领域十分广泛，包括空中交通管制、雷达天文学、空中防御系统、反导系统、对航标和其他船舶目标进行定位的船舶雷达、空中防撞击系统、海洋搜救系统、外层空间的救援和对接系统、冰雹灾害预警、测高和航班控制系统、导弹的目标定位系统、地质观测的探地雷达等。高技术雷达系统和数字信号处理结合在一起能够从具备众多高噪声的环境中提取出有用的信息。

其他和雷达相似的系统运用电磁频谱的其他领域。其中一个例子就是“激光雷达”，它运用激光器发射的可见光而不是无线电波。

雷达所提供的信息包括在其扫描仪上所显示的大小和方位，这些方位信息可以为许多需要这些信息的不同领域提供支持。雷达最初用于军事目的：确定位于空、陆、海的军事目标。军用雷达如图8.1所示，而后逐步应用于民用领域，用于定位飞机、轮船、道路等。

在航空业，飞机已经配备了雷达设备，用来对处于或者正在接近飞行线路的障碍进行预警以及提供精确的测高数据。1938年由贝尔实验室研制出的雷达装备在联合航空的飞机上，这是雷达第一次用于商业用途。这些装备了雷达的飞机可以借助雷达辅助地面控制进场系统在大雾中完成降落，在该系统中飞机的飞行轨迹可以在雷达的屏幕上面显示出来，同时运营商发送无线电降落方向信号给飞行员。

船用雷达通过测量方位和距离用于导航以防止与其他船舶相撞，当进入海滨区域以及其他固定目标区域诸如岛屿、浮标、灯塔船时，用于海上定位。在港口或者港湾，船舶交通雷达系统可以监控和调整轮船在激流中运行。警用雷达用于测量道路上车辆的速度。

气象学家将雷达用于监控冰雹，同时它也成为了对诸如雷暴、龙卷风、暴风雪、冰雹等恶劣气象短期预报和监测的基本工具。地质工作者用专门的探地雷达来绘制地壳合成图。

8.2ReadingMaterials

8.2.1MovingTargetsDetection

Theabilitytotrackmovingtargetswithairborneradarisaproblemthathasdrawnconsiderableinterestfromboththeacademicandgovernmentcommunities.Moreover,inmanycasestheopportunitynowexistsforcontinuousobservationofregionsofinterestwithairborneradars.Thus,thereisgreatincentivetobeabletoefficientlydetectandtrackindividualvehiclesoverlargeareas.

Currently,radarsystemsoperateinseveralmodesdependingontheapplication.InMovingTargetIndication(MTI)mode,theradarfocusesanarrowbeamoversmallregionsinthefieldofviewforsmallintegrationtimesontheorderofmilliseconds.HoweverMTI-moderadarssufferfromtradeoffsbetweenthesmallintegrationtime(thatleadstolowSNRvaluesandcoarseresolutions)ascomparedtothenumberofregionsthatcanbeobserved.Furthermore,MTIsystemscanonlydetectvelocitiesinasingledirection,whichallowforevasivemaneuverstoavoiddetection.

Insyntheticapertureradar(SAR)mode,animageisconstructedbyintegratingradarpulsesfromspatiallydiversepointsintheplatform’strajectory.Thissyntheticapertureleadsto2-dimensionalimagingasmuchfinerresolutionsthaninMTI-mode,duetotheabilitytouselongerintegrationtimes.Howeverwell，allthesebenefitsdonotcomeforfree.SARwasdesignedtoimagestationaryscenes.Consequently,movingtargetscausephaseerrorsinthereconstructionofaSARimagethatleadtosmearinganddisplacementofatarget'senergyusingthetoolboxprovidedbyGorhamandMoore.

Nevertheless,therehavebeenattemptstouseSARformovingtargetdetection.WernessandKirschtproposemethodsbasedonestimatingthesephaseerrors,andthenrefocusingtheimages.Fienupshowedasharpnessratiocouldbeusedtoreducethenumberoffalsealarms.However,inallofthesecases,alargecomputationalburdenwasinvolvedintheprocessingofanimage,limitingthefieldofview(FOV)thatcouldbetracked.

Tocombatthecomputationalproblem,anewapproachisconsideredwhereroadstructuresareusedaspriorknowledgeonthetrajectoriesoftargetswithinthefieldofview.Jaoshowedthatthetarget’ssignaturewithinthereconstructedimagecanbepredictedgeometricallygivenboththeplatformandthetarget’strajectories.Inpractice,theplatformtrajectoryissuppliedbyonboardGPSandIMUdata,anditcanbeassumedthatitisknowndeterministically.Inthiswork,itisassumedthatthetarget’strajectorycanbemodeledbasedonknownroadstructures,timeofday,andtrafficpatterns.

8.2.2SyntheticApertureRadar

Environmentalmonitoring,earth-resourcemapping,andmilitarysystemsrequirebroad-areaimagingathighresolutions.Manytimestheimagerymustbeacquiredininclementweatherorduringnightaswellasday.SyntheticApertureRadar(SAR)providessuchacapability.SARsystemstakeadvantageofthelong-rangepropagationcharacteristicsofradarsignalsandthecomplexinformationprocessingcapabilityofmoderndigitalelectronicstoprovidehighresolutionimagery.Syntheticapertureradarcomplementsphotographicandotheropticalimagingcapabilitiesbecauseoftheminimumconstraintsontime-of-dayandatmosphericconditionsandbecauseoftheuniqueresponsesofterrainandculturaltargetstoradarfrequencies.

Syntheticapertureradartechnologyhasprovidedterrainstructuralinformationtogeologistsformineralexploration,oilspillboundariesonwatertoenvironmentalists,seastateandicehazardmapstonavigators,andreconnaissanceandtargetinginformationtomilitaryoperations.Therearemanyotherapplicationsorpotentialapplications.Someofthese,particularlycivilian,havenotyetbeenadequatelyexploredbecauselowercostelectronicsarejustbeginningtomakeSARtechnologyeconomicalforsmallerscaleuses.

SandiahasalonghistoryinthedevelopmentofthecomponentsandtechnologiesapplicabletoSyntheticApertureRadar—40yearsinradar,antenna,andminiatureelectronicsdevelopment;30yearsinmicroelectronics;and25yearsinprecisionnavigation,guidance,anddigital-signalprocessing.Overthelastdecade,wehaveappliedthesetechnologiestoimagingradarstomeettheneedsofadvancedweaponsystems;

verificationandnonproliferationprograms;andenvironmentalapplications.Sandia’sexpertiseinelectromagnetics,microwaveelectronics,high-speedsignalprocessing,andhighperformancecomputingandnavigation,guidanceandcontrolhaveestablishedusasworldleadersinreal-timeimaging,miniaturization,processingalgorithms,andinnovativeapplicationsforSAR.

HowdoesSyntheticApertureRadar(Fig8.2)work?

AdetaileddescriptionofthetheoryofoperationofSARiscomplexandbeyondthescopeofthisdocument.Instead,thispageisintendedtogivethereaderanintuitivefeelforhowsyntheticapertureradarworks.

ConsideranairborneSARimagingperpendiculartotheaircraftvelocityasshowninthefigurebelow.Typically,SARsproduceatwo-dimensional(2-D)image.Onedimensionintheimageiscalledrange(orcrosstrack)andisameasureofthe“line-of-sight”distancefromtheradartothetarget.Rangemeasurementandresolutionareachievedinsyntheticapertureradarinthesamemannerasmostotherradars:Rangeisdeterminedbypreciselymeasuringthetimefromtransmissionofapulsetoreceivingtheechofromatargetand,inthesimplestSAR,rangeresolutionisdeterminedbythetransmittedpulsewidth,i.e.narrowpulsesyieldfinerangeresolution.

Fig8.2SyntheticApertureRadarImagingConcept

Theotherdimensioniscalledazimuth(oralongtrack)andisperpendiculartorange.ItistheabilityofSARtoproducerelativelyfineazimuthresolutionthatdifferentiatesitfromother