An Introductory Method For An Introductory Method For Evaluating the MODIS Cloud Evaluating the MODIS Cloud

Mask Over WaterMask Over WaterCorey CalvertCorey Calvert

UW/CIMSS, Madison, WisconsinUW/CIMSS, Madison, Wisconsin

Andrew HeidingerAndrew HeidingerNOAA/NESDIS Office of Research and NOAA/NESDIS Office of Research and

ApplicationsApplications

November 1, 2006November 1, 2006

OutlineOutline MethodMethod

Data usedData used

Cloud mask error estimationCloud mask error estimation

ExamplesExamples

Results / ComparisonsResults / Comparisons

Future workFuture work

Motivation?Motivation? Currently there are little or no globally Currently there are little or no globally

quantitative tools to evaluate the quantitative tools to evaluate the MODIS cloud mask over waterMODIS cloud mask over water

Evaluation/validation tools will be Evaluation/validation tools will be needed for the instruments aboard needed for the instruments aboard future satellites (e.g., GOES-R, future satellites (e.g., GOES-R, NPOESS VIIRS)NPOESS VIIRS)

MethodologyMethodology MW SST measurements relatively MW SST measurements relatively

insensitive to cloud and aerosol effectsinsensitive to cloud and aerosol effects

IR SST measurements will likely have a IR SST measurements will likely have a cool bias in the presence of cloudscool bias in the presence of clouds

Differences between IR and MW Differences between IR and MW measurements should be indicative of measurements should be indicative of cloudsclouds

DataData OI MW SST product combining TMI OI MW SST product combining TMI

and AMSR-E data and AMSR-E data (daily – 25 km) (daily – 25 km) ((www.ssmi.comwww.ssmi.com))

MOD28 - MODIS SST (day) and MOD28 - MODIS SST (day) and SST4 (night) products (1km)SST4 (night) products (1km)

MOD35 - MODIS cloud mask (1 MOD35 - MODIS cloud mask (1 km)km)

IR-MW Differences & Cloud IR-MW Differences & Cloud MaskMask

conf. cloud prob. cloud prob. clear conf. clear

Example Distribution of Example Distribution of Temperature DifferencesTemperature Differences

Calculating Error for Clear Calculating Error for Clear CategoriesCategories

Differences in Differences in region B are region B are assumed to be assumed to be attributed to non-attributed to non-cloud issues cloud issues

totalBAerror

A B

Calculating Error for Cloudy Calculating Error for Cloudy CategoriesCategories

C totalCerror

Points in region C Points in region C may be clear pixels may be clear pixels misidentified as misidentified as cloudy cloudy

AQUA & TERRAAQUA & TERRA

Latitudinal ComparisonLatitudinal Comparison

Day/Night Latitudinal Day/Night Latitudinal ComparisonComparison

Graphical Comparison Graphical Comparison (April 18, 2006)(April 18, 2006)

AQUA (daytime)

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conf. clear prob. clear prob. cloudy conf. cloudy

global error %

tropics error %

midlat error %

polar error %

global data %

tropics data %

midlat data %

polar data %

AQUA (nighttime)

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conf. clear prob. clear prob. cloudy conf. cloudy

global error %

tropics error %

midlat error %

polar error %

global data %

tropics data %

midlat data %

polar data %

TERRA (daytime)

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conf. clear prob. clear prob. cloudy conf. cloudy

global error %

tropics error %

midlat error %

polar error %

global data %

tropics data %

midlat data %

polar data %

TERRA (nighttime)

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conf. clear prob. clear prob. cloudy conf. cloudy

global error %

tropics error %

midlat error %

polar error %

global data %

tropics data %

midlat data %

polar data %

SummarySummary The MODIS cloud mask appears The MODIS cloud mask appears

consistentconsistent Between both Aqua and TerraBetween both Aqua and Terra Between day and nightBetween day and night

Latitudinal differences are seenLatitudinal differences are seen Smaller % of clear pixels and larger % of cloudy Smaller % of clear pixels and larger % of cloudy

pixels towards the polespixels towards the poles confident cloudy errors decreases towards the confident cloudy errors decreases towards the

polespoles

Future WorkFuture Work Comparison between collect 4/5Comparison between collect 4/5

Seasonal comparisonsSeasonal comparisons

Comparison between different Comparison between different instruments (e.g., AVHRR)instruments (e.g., AVHRR)

Operational Use of the MODIS Operational Use of the MODIS Cloud MaskCloud Mask

A regional real-time SST analysis is being created A regional real-time SST analysis is being created around Florida (Florida Tech)around Florida (Florida Tech) Produced 4 times per day Produced 4 times per day Combines GOES SST composites and level 2 MODIS SSTs Combines GOES SST composites and level 2 MODIS SSTs

(DB UW) via 2DVar method(DB UW) via 2DVar method Will eventually be used as lower boundary initialization Will eventually be used as lower boundary initialization

over water for ARPS/ADAS or WRF models at NWS offices over water for ARPS/ADAS or WRF models at NWS offices in FLin FL

A consistent and reliable cloud mask for the A consistent and reliable cloud mask for the MODIS SSTs is crucial to maintain the quality of MODIS SSTs is crucial to maintain the quality of the overall analysisthe overall analysis

QUESTIONS?QUESTIONS?

Acknowledgements:Acknowledgements:Richard FreyRichard Frey

Kathy StrabalaKathy Strabala