early results from the modis cloud algorithms

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


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


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


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)


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.


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.


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.


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


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


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


IR retrieval - percent liquid water


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


frequency (%)

MODIS IR phase retrieval vs. Cloud Top Temperature frequency of ice phase & Tc> 273 K


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


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


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/


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


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


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


early results from the modis cloud algorithms

Documents

warm cloud

cloud masks

clearsky cloud

govmodis cloud products

low cloud tests

nighttime low cloud

overview cloud mask

bt high cloud tests