机载气象雷达系统

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystem机载气象雷达系统AirborneWeatherRadarSystem

CivilAviationFlightUniversityofChinaTheweatherradar(WXR)systemisdesignedtoprovidetheflightcrewwithatopographicmaptypeofdisplayofmoistureladenweatherformationsinordertoavoidheavyprecipitationorturbulence.Asasecondaryfunction,theweatherradarantennacanbetilteddownwardtoprovideadisplayofmajorterrainfeaturessuchasrivers,coastlines,majormountainpeaks,andcities.AirborneWeatherRadarSystem

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemWeatherradarsystemsoperateintheX-band.

Maximumrangeofmodernradarsisabout300nm.Detectedweatherconditionsandgroundmappinginformationcanbedisplayedinthecockpit.Theantennaisnormallystabilizedusingattitudesignalsfromoneoftheverticalgyros,orinertialreferences,toavoidclutterfromgroundreturnsduringturns.

CivilAviationFlightUniversityofChinaAweatherradarsystemconsistsofareceiver/transmitter(R/T),anantenna,acontrolpanel,andindicators.Thecontrolpanelallowsthecrewtocontrolpowerapplicationandtoselectvariousmodesofweatherradaroperation.Usingthecontrolpanelselections,thereceiver/transmittergeneratesandtransmitshighenergyradiofrequency(RF)pulses.TheseRFpulsesaresenttotheantenna,andradiated.AirborneWeatherRadarSystemBasicPrinciples

CivilAviationFlightUniversityofChinaTheantennaoscillatestosweepthepencilshapedradarbeamabout90eithersideofthenose,andcanbetiltedupanddowntoabout+/-15.MoistureLadencloudsortheterrainwillreflectsomeoftheseRFpulsesbacktotheantenna.Thisreflectedenergyisreceivedbytheantenna,processedbytheR/Tunitanddisplayedontheindicators.AirborneWeatherRadarSystemBasicPrinciples

CivilAviationFlightUniversityofChina

Whattargetwillreflecttheradar’spulsesandthusbedisplayedontheindicator?

Onlyprecipitation(orobjectsmoredensethanwatersuchasearthorsolidstructures)willbedetectedbyX-bandweatherradar.Thereforeweatherradardoesnotdetectclouds,thunderstormsorturbulencedirectly.Instead,itdetectsprecipitationwhichmaybeassociatedwithdangerousthunderstormsandturbulence.

Thebestradarreflectorsareraindropsandwethail.Generally,ice,drysnow,anddryhailhavelowreflectivelevelsandoftenwillnotbedisplayedbytheradar.AirborneWeatherRadarSystemBasicPrinciples

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemBasicPrinciples

Hailusuallyhasafilmofwateronitssurface,consequently,ahailstoneisoftenreflectedasaverylargewaterparticle.Becauseofthefilmandbecausehailstonesusuallyarelargethanraindrops,thunderstormswithlargeamountsofwethailreturnstrongersignalsthanthosewithrain.Althoughwethailisanexcellentreflectorofradarenergy,somehailshaftsareextremelysmall(100yardsorless).Thesenarrowshaftsmakepoorradartargets.

Acloudthatcontainsonlysmallraindrops,suchasfogordrizzle,willnotproduceameasurableradarecho.Butiftheconditionsshouldchangeandthecloudbeginstoproducerain,itwillbedisplayonradar

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemBasicPrinciplesFigure5.1

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemBasicPrinciplesTurbulencemaybedividedintotwobasictypes:clear-airturbulence;andturbulenceassociatedwiththunderstormsandprecipitation.Theweatherradarisnotpossibletodetectclearairturbulence.Theradarreturnsareprocessedbythereceiver-transmitterandshownontheEHSIincolorasweatherormapinformation.Areasofheaviestrainfallappearinred,moderaterainfallinyellowandlightrainfallingreen.Turbulenceinformationisshownusingmagenta.ColorRainfallRateorTurbulencemm/Hr.In./Hr.BlackLessThan0.76LessThan0.03Green0.76to3.810.03to0.15Yellow3.81to12.70.15to0.5RedMoreThan12.7MoreThan0.5MagentaTurbulence

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemBasicPrinciplesFigure5.2HeaviestRainfallModerateRainfallLightRainfallNoRainfallTurbulenceAreaTurbulenceArea

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystemControlPanelTheweatherradarcontrolpanelprovidesmodeselection,systemselection,antennatiltcontrolandsystemgaincontrol.Thecontrolpanelalsoallowsfortheselectionofstabilizationandgroundcluttersuppression.WeatherRadarControlPanel

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystemGAINThesystemgainmaybeadjustedintheWX,WX+T,orMAPmodesbytheGAINcontrol.ThecontrolhastendetentedpositionsincludingtheCALposition,wherethesystemgainisautomaticallycalibrated.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

TILTTheantennatiltpositioniscontrolledbytheTILTcontrol.Thetiltrangeisfrom15°downto15°up.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

WXPressingtheWXpushbuttonswitchestheR/Tunittotheweathermode,andweatherdatawillbedisplayedontheEHSI.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

WX+TPressingtheWX+TpushbuttonswitchestheR/Tunittotheweatherplusturbulencemode,andturbulenceaswellasweatherdatawillbedisplayedontheEHSI.Turbulencewith40nmorlessisdisplayed.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

MAPPressingtheMAPpushbuttonswitchestheR/Tunittothegroundmappingmode,andterrainfeatureswillbedisplayedontheEHSI.

CivilAviationFlightUniversityofChinaFigure5.4AirborneWeatherRadarSystem

TESTThetestmodeisselectedbypressingtheTESTpushbutton.IntheTESTmode,atestpatternandthesystemstatusmessageswillbedisplayedontheEHSI.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

IDNTThispushbuttonactivatesgroundcluttersuppressiontoreducegroundclutterinWXandWX+Tmodes.

CivilAviationFlightUniversityofChinaFigure5.3AirborneWeatherRadarSystem

STABStabilizationisengagedbypressingtheSTABpushbutton.Withstabilizationselected,theantennastabilizationisprovidedbytheIRSthroughtheR/Tunit.

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemDisplay-EHSIPresentationOnmoderncommercialairplanes,theweatherradardataisusuallyshownontheEHSI.TheEHSIsshowtheweatherradardatainExpandedNAV,ExpandedVOR/ILS,MAP

andCenterMAPmodes.TheWXRswitchontheEFIScontrolpanelisusedtoturnontheweatherradarsystemandtoturnonweatherradardisplay.

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemFigure5.5

TurbulenceArea

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemTheweatherormapdisplayiscolorcoded.Targetsprovidingthemostintensereturnsareshownusingthecolorred.Targetswithlessintensityareshownusingthecolorsyellow,greenandblack.Turbulenceinformationisshownusingmagenta.HDG252MVAR/WX+T+1220MagentaRedYellowGreenGainControlDisplayModeDisplayAntennaTiltAzimuthArcWeatherRadarDisplayEHSIWeatherRadarDisplayLimit

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemOperationIn-Flight

EarlyDetectionofEn-routeWeatherTosettheantennatilttooptimizetheradar’sabilitytoquicklyidentifysignificantweather,followthesesteps:SelecttheWXmodeofoperation.AdjustBrightnesscontrolasdesired.Selectthe40or80nmrange.Adjusttheantennatiltcontroldownuntiltheentiredisplayisfilledwithgroundreturns.Slowlyworktheantennatiltupsothatgroundreturnsarepaintedonorabouttheouteronethirdoftheindicatorarea.

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemOperationIn-Flight

EarlyDetectionofEn-routeWeather

Watchthestrongestreturnsseenonthedisplay.If,astheyareapproached,theybecomeweakerandfadeoutafterbackinsidethenearlimitofthegeneralgroundreturnpattern,theyareprobablygroundreturnsorinsignificantweather.Iftheycontinuestrongafterworkingdownintothelowerhalfoftheindicator,youareapproachingahazardousstormorstormsandshoulddeviateimmediately.

Examinetheareabehindstrongtargets.Ifradarshadowsaredetectedyouareapproachingahazardousstormorstormsandshoulddeviateimmediately,regardlessoftheaircraft’saltitude.Ifweatherisbeingdetected,movetheantennatiltcontrolupanddowninsmallincrementsuntilthereturnobjectisoptimized.

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemOperationIn-Flight

BlindAlleyA“BlindAlley”or“BoxCanyon”situationcanbeverydangerouswhenviewingtheshortranges.Periodicallyswitchtolonger-rangedisplaystoobservedistantconditions.AsshowninFigure5.6,theshort-rangereturnsshowanobviouscorridorbetweentwoareasofheavyrainfallbutthelong-rangesettingshowsalargerareaofheavyrainfall.Figure5.6

CivilAviationFlightUniversityofChinaAirborneWeatherRadarSystemOperationIn-Flight

PathPlanningConsiderationsAvoidcellcontainingmagentaandredareasbyatleast20nauticalmiles.Donotdeviate

downwindunlessabsolutenecessary.Yourchancesofencounteringsevereturbulenceanddamaginghailaregreatlyreducedbyselectingtheupwindsideofthestorm.Iflookingforacorridor,remembercorridorsbetwe