MODIS meeting 11/1/2006 1

MODIS/CALIPSO Comparisons:MODIS/CALIPSO Comparisons:Cloud Detection and Altitude Cloud Detection and Altitude

Steve Ackerman, Robert Holz, and Richard FreySteve Ackerman, Robert Holz, and Richard Frey

University of Wisconsin-MadisonUniversity of Wisconsin-Madison

Cooperative Institute of Meteorological Satellite StudiesCooperative Institute of Meteorological Satellite Studies

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What is a cloud?What is a cloud?

““I know one when I see I know one when I see one.”one.”

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ARCL cloud fraction over a 30 minute time period, were ARCL ARCL cloud fraction over a 30 minute time period, were ARCL cloud fraction of less than 5% is considered clear. MODIS cloud fraction of less than 5% is considered clear. MODIS confidences of greater than 0.95 are considered clear. confidences of greater than 0.95 are considered clear. Agreement between the two approaches is 84% agreement for Agreement between the two approaches is 84% agreement for Terra, 82% for Aqua.Terra, 82% for Aqua.

ARCL ARCL Clear Clear 

ARCL ARCL Cloud Cloud 

MODIS MODIS Clear Clear 

146 146 (117)  (117)  

45 (58) 45 (58)   

MODIS MODIS Cloudy  Cloudy  

38 38 (12) (12) 

298 298 (185)  (185)  

Comparison of MODIS with 3 years of ARM site observationsComparison of MODIS with 3 years of ARM site observations

ARCL ARCL Clear Clear 

ARCL ARCL Cloud Cloud 

MODIS MODIS Clear Clear 

27.9% 27.9% (31.5)  (31.5)  

8.5% 8.5% (15.6)  (15.6)  

MODIS MODIS Cloudy  Cloudy  

7.2% 7.2% (3.2) (3.2) 

56.5% 56.5% (49.7)  (49.7)  

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The number of occurrences that MAS scene was identified as clear and the cloud physics lidar (McGill, 2002) detected a cloud optical depths (visible wavelengths). This figure suggests that the cloud limit is approximately

optical depth 0.3

What is a cloud?

Preparing for CALIPSO and MODIS:CPL and MAS

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CALIPSO Backscatter scene CALIPSO Backscatter scene

black – CALIPSO,black – CALIPSO,red – MODIS CO2red – MODIS CO2

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Derived cloud top altitude comparisonDerived cloud top altitude comparison

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Cloud masking….

Better than I expected...

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MODIS MODIS CLEARCLEAR

MODIS MODIS CLOUDYCLOUDY

CALIPSO CALIPSO CLEARCLEAR

21.6%21.6% 5.3%5.3%

CALIPSO CALIPSO CLOUDYCLOUDY

12.8%12.8% 60.2%60.2%

June 15, 2006 day and night , CALISPO CA>0.95June 15, 2006 day and night , CALISPO CA>0.95

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MODIS MODIS CLEARCLEAR

MODIS MODIS CLOUDYCLOUDY

CALIPSO CALIPSO CLEARCLEAR

25.4%25.4% 7.4%7.4%

CALIPSO CALIPSO CLOUDYCLOUDY

10.5%10.5% 56.7%56.7%

June 15, 2006 June 15, 2006 day onlyday only, CALISPO CA>0.95, CALISPO CA>0.95

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Cloud top altitudes from CALIPSO of collocated scenes on Cloud top altitudes from CALIPSO of collocated scenes on

June 15, 2006June 15, 2006

Lots of low level cloudLots of low level cloud

MODIS & MODIS & CALIPSO detect CALIPSO detect cloudcloud

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 day only, CALISPO CA>0.95June 15, 2006 day only, CALISPO CA>0.95

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 non-polar regions, June 15, 2006 non-polar regions, night onlynight only, CALISPO CA>0.95, CALISPO CA>0.95

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 daytime, ocean sun-glint freeJune 15, 2006 daytime, ocean sun-glint free

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 daytime, ocean sun-glint regionJune 15, 2006 daytime, ocean sun-glint region

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 daytime, land scenesJune 15, 2006 daytime, land scenes

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MODIS clear, CALIPSO cloudyMODIS clear, CALIPSO cloudy

June 15, 2006 daytime, desert scenesJune 15, 2006 daytime, desert scenes

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Where are these low clouds when MODIS Where are these low clouds when MODIS clear, CALIPSO Cloud?clear, CALIPSO Cloud?

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MODIS & CALIPSO see cloudMODIS & CALIPSO see cloud

Cloud Altitude Difference < 1.5 kmCloud Altitude Difference < 1.5 km

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MODIS & CALIPSO see cloudMODIS & CALIPSO see cloud

Cloud Altitude Difference > 5 kmCloud Altitude Difference > 5 km

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SummarySummary• In general, global comparison of CALIPSO and MODIS In general, global comparison of CALIPSO and MODIS

cloud detection consistent with expectations (~80% cloud detection consistent with expectations (~80% agreement).agreement).

• Consistency between comparisons ground based and Consistency between comparisons ground based and surface based active systems.surface based active systems.

• Lots of mis-matches with CALIPSO low-level cloud Lots of mis-matches with CALIPSO low-level cloud (MODIS clear, CALIPSO Cloudy).(MODIS clear, CALIPSO Cloudy).

• COCO22 cloud height biases of cirrus consistent with cloud height biases of cirrus consistent with expectations.expectations.

• Preliminary comparisons, we continue to explore Preliminary comparisons, we continue to explore differences….differences….