Image Interpretation for Weather AnalysisSlide 2Slide 3Improvement ExampleSevere Thunderstorm DetectionBoundary DetectionBlowing SnowCommon ChannelsAtmospheric AbsorptivityShortwave IRFire Detection with Shortwave IRFog DetectionSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Supercooled Cloud DetectionSupercooled ExampleSnow vs. CloudSlide 24Slide 25Urban Heat IslandsWater Vapor ChannelIdentifying Jet StreamsSlide 29Slide 30Locating Ridges and TroughsSlide 32Slide 33Slide 34Slide 35Water Vapor ExamplesSlide 37Many More ExamplesImage Interpretation for Image Interpretation for Weather AnalysisWeather AnalysisPart 2Part 23 November 20093 November 2009Dr. Steve DeckerDr. Steve DeckerImprovement ExampleImprovement ExampleRegistration GOES-12 vs. GOES-13Registration GOES-12 vs. GOES-13Battery powerBattery powerSevere Thunderstorm DetectionSevere Thunderstorm DetectionSevere thunderstorms Severe thunderstorms often have notable often have notable overshooting topsovershooting topsVis: Shadow effectsVis: Shadow effectsIR: “Enhanced-V” IR: “Enhanced-V” signaturesignatureExample: Vis IRExample: Vis IRBoundary DetectionBoundary DetectionBoundary: Subtle separation between two Boundary: Subtle separation between two air massesair massesRegion of enhanced liftingRegion of enhanced lifting–CloudsClouds–ThunderstormsThunderstormsBest seen in VisBest seen in VisLake Breeze exampleLake Breeze exampleBlowing SnowBlowing SnowCan produce whiteout conditions, even with Can produce whiteout conditions, even with no precipitationno precipitationVis Vis exampleexampleCommon ChannelsCommon ChannelsVisibleVisible–0.65 0.65 μμm (red)m (red)Infrared (IR)Infrared (IR)–10.7 10.7 μμmmWater VaporWater Vapor–6.7 6.7 μμmmShortwave IRShortwave IR–3.9 3.9 μμmmAtmospheric AbsorptivityAtmospheric AbsorptivityShortwave IRShortwave IRAn infrared window channelAn infrared window channel–Just like “longwave” IRJust like “longwave” IRAlso sees solar radiation Also sees solar radiation (blackbody curve overlap)(blackbody curve overlap)Works best for warmer tempsWorks best for warmer temps–> -30> -30°C°C–Cold clouds (e.g., cirrus) look mottledCold clouds (e.g., cirrus) look mottled–Good for fire detectionGood for fire detectionFog detectionFog detectionSupercooled vs. ice cloudsSupercooled vs. ice cloudsSnow vs. cloudSnow vs. cloudFire Detection with Shortwave IRFire Detection with Shortwave IRFires show up as “hot spots”Fires show up as “hot spots”SoCal fire exampleSoCal fire exampleFog DetectionFog DetectionEmissivity of liquid water cloud at 3.9 Emissivity of liquid water cloud at 3.9 μμmm is is less than at longer wavelengths.less than at longer wavelengths.–Fog shows up as lower temperaturesFog shows up as lower temperatures–Appears brighterAppears brighterOpposite true for ice crystals (cirrus)Opposite true for ice crystals (cirrus)Fog DetectionFog DetectionEmissivity of liquid water cloud at 3.9 Emissivity of liquid water cloud at 3.9 μμmm is is less than at longer wavelengths.less than at longer wavelengths.–Fog shows up at lower temperaturesFog shows up at lower temperatures–Appears brighterAppears brighterDifferences can be maximized by taking the Differences can be maximized by taking the difference between the longwave and difference between the longwave and shortwave IR imagesshortwave IR imagesSupercooled Cloud DetectionSupercooled Cloud DetectionSupercooled cloud droplets frequently occur Supercooled cloud droplets frequently occur for -20for -20°C°C < T < 0 < T < 0°C°CDetection methodDetection method–Identify cloud-top temperatures conducive for Identify cloud-top temperatures conducive for supercooled droplets using longwave IRsupercooled droplets using longwave IR–Just like fog/stratus droplets, supercooled Just like fog/stratus droplets, supercooled droplets emit less radiation in shortwave IRdroplets emit less radiation in shortwave IRSupercooled ExampleSupercooled Examplehttp://weather.msfc.nasa.gov/sport/goes_imager/goes_imager.htmlSnow vs. CloudSnow vs. CloudDuring the day, low clouds will reflect more During the day, low clouds will reflect more solar radiation than snow at 3.9 solar radiation than snow at 3.9 μμmm, so low , so low clouds appear darker (more signal) than clouds appear darker (more signal) than snow.snow.Urban Heat IslandsUrban Heat IslandsShortwave IR is more Shortwave IR is more sensitive to emissions sensitive to emissions from warmer from warmer temperaturestemperatures–Urban heat islands Urban heat islands show up bettershow up betterWater Vapor ChannelWater Vapor ChannelNot an IR windowNot an IR window–Does not see the ground (Does not see the ground (ExceptionException))Absorbed/emitted by water vaporAbsorbed/emitted by water vaporColder temperatures imply:Colder temperatures imply:–More moisture in the mid and upper More moisture in the mid and upper tropospheretroposphere–Possible regions of ascentPossible regions of ascentTemperature differences important; not their Temperature differences important; not their magnitudesmagnitudesExampleExampleIdentifying Jet StreamsIdentifying Jet StreamsJet StreamsJet Streams–Ribbons of quickly moving air near the tropopauseRibbons of quickly moving air near the tropopause–Separate air massesSeparate air masses–Support active weatherSupport active weatherVis: Band of cirrus clouds on equatorward sideVis: Band of cirrus clouds on equatorward sideVapor: Strong moisture gradientVapor: Strong moisture gradient–Dry air polewardDry air poleward–Moist air equatorwardMoist air equatorwardLocating Ridges and TroughsLocating Ridges and TroughsUpper tropospheric flow often contains a Upper tropospheric flow often contains a ridge/trough patternridge/trough patternClouds often occur downstream of troughs, but Clouds often occur downstream of troughs, but upstream of ridgesupstream of ridgesIf ridge has small amplitude, clouds may “spill If ridge has small amplitude, clouds may “spill over” ridgeover” ridgeCloud band ahead of trough often indicates “warm Cloud band ahead of trough often indicates “warm conveyor belt” immediately ahead of a surface conveyor belt” immediately ahead of a surface cold frontcold front–Southern extent of solid band marks trough axisSouthern extent of solid band