Satellite Derived Mid- Satellite Derived Mid- Upper Level WindsUpper Level Winds

Cegeon ChanCegeon ChanMET 315: Remote SensingMET 315: Remote Sensing

•ImportanceImportance

•InstrumentsInstruments

•Location TrackingLocation Tracking

•Height AssignmentHeight Assignment

•Quality ControlQuality Control

http://apollo.lsc.vsc.edu/classes/remote/index.html

•AccuracyAccuracy

•SummarySummary

OutlineOutline

ImportanceImportance•Over oceanic Over oceanic regionsregions•Dvorak Dvorak TechniqueTechnique•Wind vectorsWind vectors•Numerical Numerical Weather Weather PredictionPrediction

1)1) cloud-drift cloud-drift

2) Water Vapor2) Water Vapor

3) Sounder WV3) Sounder WV

4) Visible4) Visible

Different TypesDifferent Types

0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%

100-250mb

250-400mb

400-600mb

600-1000mb

Cloud Drift Imager Water Vapor Visible winds Sounder Water Vapor

What does it look like?What does it look like?

•Capable of Capable of gathering gathering water vapor water vapor fieldsfields•Measure Measure infrared infrared energyenergy

SounderSounderImagerImager

•Responsible for Responsible for NH and SHNH and SH•Low FrequencyLow Frequency

•Responsible for Responsible for the tropicsthe tropics•High FrequencyHigh Frequency

Tracking BackgroundTracking Background•Similar to cloud trackingSimilar to cloud trackingAlgorithm is housed Algorithm is housed within McIdas!within McIdas!•Very sensitiveVery sensitive•Rule: at least 3 images to Rule: at least 3 images to derive winds to produce 2 derive winds to produce 2 vectorsvectorsMeasures consistency Measures consistency between successive imagesbetween successive images

Tracking ProcedureTracking Procedure•Take a small Take a small areaarea•Isolate the Isolate the lowest cloud lowest cloud brightness brightness temperature temperature within a pixel within a pixel arrayarray

•Compute bi-Compute bi-directional directional gradients are gradients are computedcomputed•Cloud-free Cloud-free environmentsenvironments•Generally in Generally in moist regimesmoist regimes

Tracking Procedure (cont.)Tracking Procedure (cont.)

Height AssignmentHeight Assignment•Goal is to Goal is to ascertain the height ascertain the height level of the feature level of the feature you trackedyou tracked•Can be Can be complicated if complicated if there are multiple there are multiple moist layersmoist layers

S. Velden, Christopher, Christopher M. Hayden, Steven J. Nieman, W. Paul Menzel, Steven Wanzong, James S. Goerss, 1997: Upper-Tropospheric Winds Derived from Geostationary Satellite Water Vapor Observations. Bulletin of the American Meteorological Society: Vol. 78, No. 2, pp. 173–173

•Convert Convert measured measured radiance into radiance into Brightness Brightness TemperatureTemperature•This value is This value is collocated with collocated with a model guess a model guess temperaturetemperature

Height Assignment Height Assignment (more)(more)

•Slow – using cloud Slow – using cloud drift windsdrift winds•Add 8% for 10m/sAdd 8% for 10m/s•Incorporate Incorporate satellite winds into satellite winds into analysis analysis •Remove those Remove those differing differing significantly from significantly from analysisanalysis

Quality Control AlgorithmQuality Control Algorithm

•Yellow = minus Yellow = minus satellitesatellite•Red = Plus satelliteRed = Plus satellite

Accuracy – how good is it?Accuracy – how good is it?•A particular A particular single level single level does not does not represent a represent a layerlayer•Generally Generally good for 50 good for 50 mb mb

Sources of ErrorsSources of Errors•Assumption of clouds and water vaporAssumption of clouds and water vapor

•Image registration errorsImage registration errors

•Target identification and tracking errorsTarget identification and tracking errors

•Inaccurate height assignmentInaccurate height assignment

SummarySummary•Great applications – oceanic analysis, Great applications – oceanic analysis, tropical cyclonestropical cyclones•Improved numerical weather analysis and Improved numerical weather analysis and prediction systemsprediction systems•Similar to cloud tracking methodSimilar to cloud tracking method•Tendency to be slowTendency to be slow

Got Questions? Got Questions?