题目内容：
PleaseFastenYourSeatbeltsSevereturbulence（湍流）cankillaircraftpassengers.Now,intestflightsovertheRockyMountains,NASA（美国航空航天局）engineershavesuccessfullydetectedclear-airturbulenceupto10secondsbeforeanaircrafthitsit.
Clear-airturbulenceoftencatchespilotsbysurprise.Invisibletoradar,itisdifficulttoforecastandcanhurl（用力抛出去）passengersaboutthecabin.InDecember1997,onepassengerdiedandahundredotherswereinjuredwhenunexpectedroughaircausedaUnitedAirlinesflightoverthePacifictodrop300metresinafewseconds.
However,passengerscanavoidseriousinjurybyfasteningtheirseatbelts.“Itistheonlyantidote（对策）forthissortofthings,”saysRodBogue,projectmanageratNASA’sDrydenFlightResearchCenterinEdwards,California.
Thecentre’snewturbulencedetectorisbasedonlidar,orlaserradar,Laserpulsesaresentaheadoftheplaneandthesearethenreflectedbackbyparticlesintheair.ThetechniquedependsontheDopplereffect.Thewavelengthofthelightshiftsaccordingtothespeedatwhichtheparticlesareapproaching.Incalmair,thespeedequalstheplane’sairspeed.Butastheparticlesswirl（打漩）inroughair,theirspeedofapproachincreasesordecreasesrapidly.Therateofchangeinspeedcorrespondstotheseverity（激烈程度）oftheturbulence.
Inaseriesofteststhatbeganlastmonth,aresearchjetflewrepeatedlyintodisturbedairoverthemountainridges（山脉）nearPueblo,Colorado.Thelidardetectorspottedturbulencebetween3and8kilometresahead,anditsforecastsofstrengthanddurationcorrespondedclo
参考答案：
答案解析：