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cloud detection optical, microphysical, and cloud top properties. Early Results from the MODIS Cloud Algorithms. S. Platnick 5,2 , S. A. Ackerman 1 , M. D. King 2 , W. P. Menzel 3,1 , B. A. Baum 4,1 , et al. - PowerPoint PPT Presentation
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Early Results from theEarly Results from theMODIS Cloud Algorithms MODIS Cloud Algorithms
cloud detectionoptical, microphysical, and cloud top properties
S. Platnick5,2, S. A. Ackerman1, M. D. King2, W. P. Menzel3,1,
B. A. Baum4,1, et al.
AGU Fall Meeting AGU Fall Meeting San Francisco, CA San Francisco, CA December 19, 2000December 19, 2000
1 U. Wisconsin/CIMSS, 2 NASA GSFC, 3 NOAA NESDIS, 4 NASA LaRC, 5 UMBC/JCET
Outline
MODIS - a quick introductionMODIS - a quick introduction MODIS cloud productsMODIS cloud products Algorithm descriptions and example retrievalsAlgorithm descriptions and example retrievals Data statusData status
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
MODIS (MODerate resolution Imaging Spectroradiomter)
Filter radiometer, 4 detector arrays, 36 spectral bands; Filter radiometer, 4 detector arrays, 36 spectral bands; 250 m, 500 m, 1 km spatial resolution250 m, 500 m, 1 km spatial resolution
Onboard calibration via Onboard calibration via Solar DiffuserSolar Diffuser//Stability MonitorStability Monitor, , Spectral Radiometric Calibration AssemblySpectral Radiometric Calibration Assembly instrumentsinstruments
First light on 24 February 2000 (Terra launch 18 Dec First light on 24 February 2000 (Terra launch 18 Dec 1999)1999)
Science teams organized into atmosphere, land, and Science teams organized into atmosphere, land, and ocean discipline groupsocean discipline groups
MODIS instrument highlights
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
MODIS Atmosphere Global 19 April 2000L1B True color RGB (0.65, 0.56, 0.47 µm bands)
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000example data granule coverage (5 min)example data granule coverage (5 min)
Pixel level products (Level 2) overviewPixel level products (Level 2) overview
– – Cloud mask for determining “clear-sky”Cloud mask for determining “clear-sky”
– – Cloud top propertiesCloud top properties
– – Cloud optical, microphysical properties Cloud optical, microphysical properties (optical thickness, effective particle size, water (optical thickness, effective particle size, water path, thermodynamic phase, cirrus reflectance) path, thermodynamic phase, cirrus reflectance)
Unique aspectsUnique aspects– – New algorithms from greater New algorithms from greater spectralspectral coverage coverage– – Heritage algorithms at higher Heritage algorithms at higher spatialspatial resolution resolution
– – Includes Includes QAQA (processing and assessment info) (processing and assessment info)
MODIS cloud products, granule level
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Gridded time-average products (Level 3)Gridded time-average products (Level 3)
– – Daily, 8 day, monthly composites containing all Daily, 8 day, monthly composites containing all
atmosphere productsatmosphere products
– – 1˚ x 1˚ equal angle grid1˚ x 1˚ equal angle grid
– – mean, standard deviation, marginal andmean, standard deviation, marginal and
joint probability distributionsjoint probability distributions
– – quick look available on the webquick look available on the web
details at the MODIS atmosphere web pagedetails at the MODIS atmosphere web page
http://modis-atmos.gsfc.nasa.govhttp://modis-atmos.gsfc.nasa.gov
MODIS cloud products, global composites
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Cloud mask(S. Ackerman, R. Frey, K. Strabala – U. Wisconsin/CIMSS)
Bottom of the algorithmic “food chain”, input to all Bottom of the algorithmic “food chain”, input to all MODIS products. MODIS products.
1 km nadir spatial resolution day & night, (250 m day) 1 km nadir spatial resolution day & night, (250 m day) 17 spectral bands (0.55-13.93 µm, incl. 1.38 µm)17 spectral bands (0.55-13.93 µm, incl. 1.38 µm)
– – 11 spectral tests (function of 5 ecosystems)11 spectral tests (function of 5 ecosystems)
–– temporal consistency test over ocean, desert (nighttime)temporal consistency test over ocean, desert (nighttime)
– – spatial variability test over oceanspatial variability test over ocean
48 bits per pixel48 bits per pixel including individual test results and including individual test results and processing path; generation of clear sky mapsprocessing path; generation of clear sky maps
Bits 1,2 give combined test results as: Bits 1,2 give combined test results as: confident clearconfident clear, , probably clearprobably clear, , uncertainuncertain, , obstructed/cloudyobstructed/cloudy (clear sky (clear sky conservative)conservative)
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Cloud mask, cont.
Spectral tests use fuzzy thresholds, examples includeSpectral tests use fuzzy thresholds, examples include
– – low cloud tests: low cloud tests:
3.9 µm - 11 µm BT3.9 µm - 11 µm BT
– – high cloud tests: high cloud tests:
13.9 µm (CO13.9 µm (CO22), 1.38 µm (H), 1.38 µm (H22O), 11-12 µm BTO), 11-12 µm BT
– – 1.6 µm snow/ice test1.6 µm snow/ice test
– – NIR/VIS reflectance test; IR tests (dependent on NIR/VIS reflectance test; IR tests (dependent on sfc emissivity, PW, aerosols); et al.sfc emissivity, PW, aerosols); et al.
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Ackerman, S. A. et al. 1998: JGR, 103, 32141-32157.
Cloud mask, validation activities
Mask consistent with radar/lidar cloud boundary Mask consistent with radar/lidar cloud boundary measurements at Oklahoma ARM CART site measurements at Oklahoma ARM CART site and ER-2 observations during spring 2000 and ER-2 observations during spring 2000 campaign (including correct snow identification).campaign (including correct snow identification).
Improvements being made for sun glint, warm Improvements being made for sun glint, warm cloud in arid ecosystems, Antarctica, nighttime cloud in arid ecosystems, Antarctica, nighttime low cloud over land, nighttime snow/ice surfaceslow cloud over land, nighttime snow/ice surfaces
Regional/global validation is ongoing. Gobal Regional/global validation is ongoing. Gobal clear sky composite images being used to clear sky composite images being used to identify problem regions.identify problem regions.
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
aa
MODIS cloud mask exampleMODIS cloud mask example(confident clear is green, probably clear is blue, uncertain is red, cloud is white)
1.6 µm image 0.86 µm image 11 µm image 3.9 µm image cloud mask
Snow test(impacts choice of tests/thresholds)
VIS test(over non-snowcovered areas)
3.9 - 11 BT test
for low clouds
11 - 12 BT test (primarily for
high cloud) 13.9 µm
high cloud test(sensitive in cold regions)
MODIS 5-8 September 2000Band 31 (11.0 µm) Daytime Clear sky Brightness Temperature
MODIS 5-8 September 2000Band 1, 4, 3 (R/G/B) Daytime Clear sky Reflectance Composite
Cloud top properties(P. Menzel, R. Frey, K. Strabala, L. Gumley, et al. – NOAA NESDIS, U. Wisc./CIMSS)
Cloud top pressure, temperature, effective emissivity Cloud top pressure, temperature, effective emissivity
Retrieved for every 5x5 box of 1 km FOV’s, when at Retrieved for every 5x5 box of 1 km FOV’s, when at least 5 FOV’s are cloudy, day & nightleast 5 FOV’s are cloudy, day & night
COCO22 Slicing technique (5 bands, 12.0-14.2 µm) Slicing technique (5 bands, 12.0-14.2 µm)
– – ratio of cloud forcing in 2 nearby bandsratio of cloud forcing in 2 nearby bands
–– retrieve retrieve ppcc; T; Tcc from temperature profile from temperature profile
–– most accurate for high and mid-level cloudsmost accurate for high and mid-level clouds Previously applied to HIRS (NOAA POES, 20 km). Previously applied to HIRS (NOAA POES, 20 km).
MODIS 1st satellite sensor capable of COMODIS 1st satellite sensor capable of CO22 slicing at slicing at
high spatial resolution.high spatial resolution.S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Activities proceeding via early ER-2 effort (March Activities proceeding via early ER-2 effort (March 2000 with lidar and HIS IR interferometer), and 2000 with lidar and HIS IR interferometer), and NOAA HIRS intercomparisonsNOAA HIRS intercomparisons
Cloud top pressure compares well with HIRS and Cloud top pressure compares well with HIRS and aircraft validation,better than 50 mb.aircraft validation,better than 50 mb.
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Cloud top properties, validation activities
Frey, R. A. et al, 1999: JGR , 104, 24547-24555.
CO2 slicing
Technique:Technique:
- ratio of cloud forcing at two - ratio of cloud forcing at two near-by wavelengthsnear-by wavelengths
- - effective emissivityeffective emissivity includes includes cloud fraction in 5x5 boxcloud fraction in 5x5 box
- actual cloud emissivity - actual cloud emissivity assumed same for each bandassumed same for each band
- radiance gradient used when - radiance gradient used when clear sky not availableclear sky not available
The more absorbing bands The more absorbing bands are more sensitive to high are more sensitive to high clouds, weighting functions clouds, weighting functions
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Frey, R. A. et al, 1999: A comparison of cloud top heights computed from airborne lidar and MAS radiance data. J. Geophys. Res., 104, 24547-24555.
1000
100
10
0.0 0.2 0.4 0.6 0.8 1.0P
ress
ure
(mb)
Weighting Function dt(,p)/d ln p
Channel 32 33 34 35 36
Central Wavelength (µm)
12.020 13.335 13.635 13.935 14.235
36
1.2
35
34
33
32
Cloud Mask – MODIS 12 March 2000, 1730 UTC
snowsnow
clear=green cloud=white uncertain=red
MODIS band 31MODIS band 3111 µm11 µm Cloud MaskCloud Mask
ARM CART siteARM CART site
Cloud Top Pressure – MODIS 12 March 2000, 1730 UTC
MODIS band 31MODIS band 3111 µm11 µm
Cloud top pressureCloud top pressure
900-1000 mb=purple 500-600 mb=blue 300-400 mb=red
ARM CART siteARM CART site
Comparison of ER2 lidar (nadir view), HIRS (3 hrs later), RAOB, & MODIS Cloud Propertiesover ARM CART site, Oklahoma
MODIS and CHAPS CO 2 -slicing Cloud Effective Emissivity
17:30 UTC 12 March, 2000
36-40 North Latitude and 90-100 West Longitude
Cloud Effective Emissivity (%)
Fre
quen
cy (
%)
0
10
20
30
40
50
0-10 10-20 20-30 30-40 40-50 50-60 60-70 70-80 80-90 90-100
Total Observations:CHAPS 609MODIS 13586
Open Bars: CHAPSSolid Bars: MODIS
MODIS and CHAPS CO 2 -slicing Cloud Top Pressures
17:30 UTC 12 March, 2000
36-40 North Latitude and 90-100 West Longitude
Pressure (mb)
Freq
uenc
y (%
)
0
10
20
30
40
50
100-
199
200-
299
300-
399
400-
499
500-
599
600-
699
700-
799
800-
899
900-
999
1000
Open Bars: CHAPSSolid Bars: MODIS
Total Observations:CHAPS 609MODIS 13586
Clear Sky
lidarlidar
effective emissivity vs. HIRSeffective emissivity vs. HIRSCTP vs. CTP vs. HIRSHIRS
Cloud top Pressure Cloud top Temperature
Cloud Fraction Cloud Effective Emissivity
MODIS 5-8 September 2000
IR thermodynamic phase algorithm (B. Baum, S. Ackerman, K. Strabala – NASA LaRC, U.W. CIMSS)
Tri-spectral Tri-spectral methodmethod, , 5 km 5 km resolutionresolution
NIR, MWIR NIR, MWIR reflectance reflectance technique technique being being developeddeveloped
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
ice cloudApril 1996Success
water cloudJan 1993TOGA/COARE
Strabala, Menzel, and Ackerman, 1994, JAM, 2, 212-229.Baum et al, 2000, JGR, 105, 11781-11792.
Ice
Water
Mixed Phase
Uncertain
MODIS cloud thermodynamic phase - IR algorithmMODIS cloud thermodynamic phase - IR algorithm
Clouds over Southern IndiaClouds over Southern India19 April 200019 April 2000
VISVIS IR windowIR window cloud phasecloud phase
MODIS 5-8 September 2000
IR retrieval - percent liquid water
MODIS 5-8 September 2000
IR retrieval - percent ice water
MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & Tc < 253 K
statistics from 5 Sept day and night, 60ºN-60ºS, water surface only
frequency (%)
frequency (%)
MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & 253< Tc< 273 K
statistics from 5 Sept day and night, 60ºN-60ºS, water surface only
frequency (%)
MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & Tc> 273 K
statistics from 5 Sept day and night, 60ºN-60ºS, water surface only
Cloud optical, microphysical properties(M. D. King, S. Platnick, M. Gray, E. Moody, J. Li, S.-C. Tsay, et al. – NASA GSFC, UMBC)
Optical thickness, particle size (effective radius), Optical thickness, particle size (effective radius), water pathwater path
1 km spatial resolution, daytime only, liquid water and 1 km spatial resolution, daytime only, liquid water and ice cloudsice clouds
Land, ocean, snow/sea ice surfacesLand, ocean, snow/sea ice surfaces Solar reflectance technique, VIS through MWIR Solar reflectance technique, VIS through MWIR
(0.65, 0.86, 1.2, 1.6, 2.1, 3.7 µm) (0.65, 0.86, 1.2, 1.6, 2.1, 3.7 µm)
MODIS 1MODIS 1stst satellite sensor with all useful satellite sensor with all usefulSWIR, MWIR bandsSWIR, MWIR bands
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Cloud optical, microphysical properties, cont.
Required input:Required input:
– – cloud mask (cloud mask (tuned for cloudy not clear using tuned for cloudy not clear using individual cloud mask testsindividual cloud mask tests))
– – cloud top temperature for 3.7 µm retrievalcloud top temperature for 3.7 µm retrieval
– – cloud top pressure for atmospheric correction cloud top pressure for atmospheric correction (being implemented(being implemented))
– – cloud phase (cloud phase (currently derived from individual cloud currently derived from individual cloud mask tests, not IR or solar testsmask tests, not IR or solar tests))
– – surface albedo (surface albedo (currently assigned from IGBPcurrently assigned from IGBPecosystem map & NISE snow/ice data setecosystem map & NISE snow/ice data set))
Early validation effort as part of SAFARI 2000Early validation effort as part of SAFARI 2000
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
MODIS SAFARI granule RGB composite13 September 2000, 0925 UTC
Namibia
Etosha Pan
Angola
marine marine stratocumulusstratocumulus
ER-2 ground trackER-2 ground track
Namibia
Angola
Botswana
South Africa
Zambia
(>99%)
(>95%)
(>66%)
Data summary Atmosphere L2 products processed on P.I. system at Atmosphere L2 products processed on P.I. system at
GSFC (except cloud mask)GSFC (except cloud mask) Cloud products archived at GSFC DAACCloud products archived at GSFC DAAC
– – series starts at 8/20/00 for L2, 10/31/00 for L3(1d)series starts at 8/20/00 for L2, 10/31/00 for L3(1d) Current archived products are “beta” releaseCurrent archived products are “beta” release
– – early data product, useful for familiarity with data early data product, useful for familiarity with data formats/parameters, minimal validation, temporaryformats/parameters, minimal validation, temporary
Consistent processing time series (instrument bias Consistent processing time series (instrument bias settings, L1B algorithm) underwaysettings, L1B algorithm) underway
Order through EOS Data GatewayOrder through EOS Data Gateway
- details at- details at http://modis.gsfc.nasa.gov/DATA/http://modis.gsfc.nasa.gov/DATA/
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Data summary, cont.
Data file infoData file info–“–“MOD35” cloud mask ~ 48 MB/granule daytimeMOD35” cloud mask ~ 48 MB/granule daytime
–“–“MOD06” cloud product ~ 65 MB/granule daytime, MOD06” cloud product ~ 65 MB/granule daytime, 16 MB nighttime, 12 GB/day16 MB nighttime, 12 GB/day
- L3 atmospheres ~ 400-800 MB/day- L3 atmospheres ~ 400-800 MB/day
- L1B ~ 340 MB/granule, 70 GB/day- L1B ~ 340 MB/granule, 70 GB/day
L2 production system limitsL2 production system limits – – currently running at approximately “1x”, not sufficient currently running at approximately “1x”, not sufficient
for reprocessing needs for reprocessing needs
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
minimumminimum maximummaximum
standard standard deviationdeviation
meanmean
L3 optical thickness (liquid water) statistics, 10/2/00, from atmo web page L3 optical thickness (liquid water) statistics, 10/2/00, from atmo web page
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
Algorithms summary
MODIS provides an unprecedented opportunity for cloud MODIS provides an unprecedented opportunity for cloud and other atmospheric studiesand other atmospheric studies
– – 36 36 spectralspectral channels, high channels, high spatialspatial resolution resolution Comprehensive set of cloud algorithmsComprehensive set of cloud algorithms Archive of pixel level retrievals, global statisticsArchive of pixel level retrievals, global statistics Product intercomparison for small number of selected Product intercomparison for small number of selected
day(s) proven useful day(s) proven useful Validation activities ongoing (gnd. based, in situ, aircraft, Validation activities ongoing (gnd. based, in situ, aircraft,
satellite intercomparisons, etc.); detailed plans on satellite intercomparisons, etc.); detailed plans on atmosphere web siteatmosphere web site
S. Platnick, S. Platnick, AGUAGU, 19 Dec. 2000, 19 Dec. 2000
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