MODIS on Terra and Aqua: Moderate collecting longterm global observation of atmosphere

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Evaluation of MODIS-Derived Cloud Products Using
the ARM SGP Data
Gerald G. Mace and Yuying ZhangUniversity of
Utah Steven Platnick and Michael D. King NASA
Goddard Space Flight Center Patrick Minnis NASA
Langley Research Center Ping Yang Texas A and M
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• MODIS Moderate Resolution Imaging
  Spectroradiometer
• Currently in orbit on Terra (3/2000) and Aqua
  (6/2002)
• Spectral range (visible, near IR, thermal IR)
• Swath 2300 km
• Operational Cloud Property Processing
  Algorithms
• MODIS Atmospheres (Platnick and King)
• MODIS-CERES (Minnis)

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Cirrus Cloud Property Comparison Ground-Based
Data
Cirrus Algorithm

• Reflectivity-Radiance
• Uses AERI radiance and layer-mean radar Z
• Searches for a first order gamma distribution of
  cloud particles that simultaneously give the
  correct Z and Emittance.
• produces layer mean PSD at 10 minute resolution

Millimeter Cloud Radar
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Cirrus Cloud Property Comparison Comparison
Technique
Bootstrapping Approach Aircraft Ground Sate
llite
aircraft measured IWP (g/m2)
RMS 25
retrieval IWP (g/m2)
aircraft measured re (µm)
RMS 20
retrieval re (µm)
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Ground-Based Data Source ARM sites
(Atmospheric Radiation Measurement program
supported by the U.S. Department of Energy )
aircraft
ground
satellite
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COMPARISON TECHNIQUE
March 6, 2001 Height-Time cross section of radar
reflectivity
Wind profiler data observed by the NOAA 404 MHz
wind profiler near Lamont Oklahoma
Height (km)
Height (km)
Horizontal Wind Speed (m/s)
Horizontal Wind Direction (Degree)
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Cirrus Cloud Property Comparison Case Study 6
March 2001
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COMPARISON TECHNIQUE
Visible image of cirrus observed by MODIS at 1735
UTC in the vicinity of the ARM SGP on 6 March
2001. The SGP central facility is shown with the
light green square. The yellow lines show
latitude and longitude.
SGP
selected area
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frequency
frequency
IWP (g/m2)
Effective radius (µm)
frequency
Optical thickness
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CLOUD PROPERTIES FOR INDIVIDUAL CASES
Comparison between ground-based data and
MODIS-CERES
Comparison between ground-based data and MOD06
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March 22, 2001
MODIS 1.38 micron imagery
MMCR overcast thin cirrus cloud MODIS 688
pixels detected cirrus in totally 2768 pixels
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STATISTICAL COMPARISON
Time period March 2000-July 2001 Satellite
data 648 events when Terra passed near SGP
site 100 km x 100 km centered on ARM SGP
site totally 895,243 MODIS
retrievals Ground-based data a total of
5772 3-minute averages about 300 hours of
cirrus
Data distribution
Optical thickness lt0.5 0.51.0
1.01.5 1.52.0 2.03.0 3.04.0
4.05.0 MOD06 pixels 811 2036
160,378 93,496 189,675 159,460
142,582 ARM SGP points 3131 1003
522 287 331 205
123
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optical thickness 0-0.5
0.5-1.0
1.0-3.0
3.0-5.0
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CONCLUSION

• The cirrus cloud properties reported in the MOD06
  and MODIS-CERES retrievals agree reasonably well
  with the aircraft-validated ground-based cirrus
  cloud properties
• The MOD06 retrievals are biased large when
  optical thickness of cirrus is less than 1.0
• The source of disparity in the spatially-averaged
  MOD06 results occurred preferentially when the
  optical thickness of the cirrus retrieved from
  the radar data was less than about 1.0
• occurrence frequency of optically thin
  cirrus at 80
• a source of uncertainty for MODIS level-3
  data

FUTURE WORK

• Continue to compare for more available cases
• Extend the validation work to the other ARM sites