liang apeis capacity building workshop on integrated environmental monitoring of asia-pacific region...
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APEIS Capacity Building Workshop on Integrated Environmental Monitoring of Asia-Pacific Region
20-21 September 2002, Beijing,, China
Atmospheric Correction of Optical Remotely Sensed Imagery
Shunlin Liang
Department of Geography
University of Maryland at College Park, USA
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Outline
IntroductionMODIS atmospheric correction algorithmsOther correction methods and examplesSummary
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Atmospheric effects
Gaseous AbsorptionWater vaporOzone ( ) and others
Particle ScatteringRayleigh (Molecular)Aerosol (large sizes)
2CO3O
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Water vapor absorption
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Water vapor
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Water Vapor
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Ozone
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Ozone
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CO2
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CO2
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Total transmittance(mid-latitude summer, nadir viewing)
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Rayleigh Scattering
* Optical depth decreases quickly as wavelength
* Very stable in both time and space
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Aerosol scattering
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Outline
IntroductionMODIS atmospheric correction algorithmsOther correction methods and examplesSummary
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MODIS atmospheric correction
Water absorption estimation and correction (MOD05) – Dr. Gao Bo-Cai
Aerosol estimation (MOD04) – Dr. Yoram Kaufman
Surface reflectance retrieval (MOD-09) – Dr. Eric Vermote
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Differential absorption Methods for estimating water vapor content
Two-band ratio:
Three-band ratio:
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Differential absorption Methods for estimating water vapor content
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Aerosol Climatology
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Aerosol climatology
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Estimation of aerosol optical depth(dark object approach)
Step 1: low surface reflectance at 2.2 um
Step 2: surface reflectance at red and blue
Step 3: aerosol properties from TOA radiances
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Estimation of aerosol optical depth(dark object approach)
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Estimation of aerosol optical depth(dark object approach)
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Surface reflectance retrieval
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Major limitations (dark-object approaches)
Relies on empirical statistical relations
works only over vegetated surfaces
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Outline
IntroductionMODIS atmospheric correction algorithmsOther correction methods and examplesSummary
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Other atmospheric correction methods
Invariant object regression method for temporal evaluation (Hall, et al.,
1991): find a set of pixels whose reflectance values do not change significantly
under different solar and atmospheric conditions simple and easy implementation relative correction uniform aerosol distribution
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Other atmospheric correction methods
Histogram matching technique (ATCOR2 in ERDAS; Richter, 1996): identify hazy regions using the Tasseled Cap
transformationmatch histograms of both clear and hazy regions.Tasseled Cap transformation does not always work approximate correction, not well for heterogeneous
aerosols uniform landscape
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Other atmospheric correction methods
Dark-object algorithms for TM Imagery
Liang S., H. Fallah-Adl, S. Kalluri, J. JaJa, Y. J. Kaufman, and J. R. G. Townshend, (1997), An Operational Atmospheric Correction Algorithm for Landsat Thematic Mapper Imagery over the Land, J. Geophys. Res. - Atmosphere,102:17173-17186.
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Atmospheric correction examples (Liang, et al., J. Geophys. Res., 1997)
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Cluster matching method
Liang, S., H. Fang, M. Chen, (2001), Atmospheric Correction of Landsat ETM+ Land Surface Imagery: I. Methods, IEEE Transactions on Geosciences and Remote Sensing 39:2490-2498.
Liang, S., H. Fang, J. Morisette, M. Chen, C. Walthall, C. Daughtry, and C. Shuey, (2002), Atmospheric Correction of Landsat ETM+ Land Surface Imagery: II. Validation and Applications, IEEE Transactions on Geosciences and Remote Sensing, in press
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Are bands 4,5 &7 hazy or there shadows?
Histogram matching
Clustering analysis
Determining clear and hazy regions
Determining reflectance of clear regions
Mean reflectance matching of each cluster in both clear & hazy regions
Look-up tables searching for aerosol optical depth
Spatial smoothing of the estimated aerosol optical depth
Reflectance retrieval by considering adjacency effects
YES
NO
Are near-IR bands hazy or there shadows?
Histogram matching
Clustering analysis
Determining clear and hazy regions
Determining reflectance of clear regions
Mean reflectance matching of each cluster in both clear & hazy regions
Look-up tables searching for aerosol optical depth
Spatial smoothing of the estimated aerosol optical depth
Reflectance retrieval by considering adjacency effects
YES
NO
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ETM+ atmospheric correction: Case1
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ETM+ atmospheric correction: case1
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ETM+ atmospheric correction: Case 2
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ETM+ atmospheric correction: case 2
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ETM+ atmospheric correction: case 3
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ETM+ atmospheric correction: case 3
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AVIRIS ( Airborne Visible InfraRed Imaging Spectrometer)
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AVIRIS Imagery of Parana, Brazil acquired on August 23, 1995
Band 18 (549nm) Band 26 (627nm) Band 34 (673nm)
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Atmospheric correction of AVIRIS Imagery
Composite imagery of Parana, Brazil, August 23, 1995 Bands 26 (627nm), 34(673nm) and 46 (788nm)
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Sea-viewing Wide Field-of-view Sensor (SeaWiFS)
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SeaWiFS imagery of Washington DC
area, Nov. 6, 2000
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SeaWiFS imagery of Washington
DC area, Nov. 6, 2000
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MODIS (Moderate Resolution Imaging Spectroradiometer)
MODIS is the key instrument aboard the Terra and Aqua satellites. Terra/Aqua MODIS is viewing the entire Earth's surface every 1 to 2
days, acquiring data in 36 spectral bands.
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MODIS imagery (northeastern coast,
China May 7, 2000)
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MODIS imagery of China northeastern
coast, May 7, 2000
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MODIS imagery of China northeastern
coast, May 7, 2000
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Summary
Atmospheric correction is very critical in monitoring land surfaces, particularly for regions with frequently cloudy and hazy conditions
There exist many different algorithms, but further developments are needed for global applications (inter-comparision, calibration and validation)
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References
Kaufman, Y, 1989. The Atmospheric Effect on Remote Sensing and Its Correction, in Theory and Applications of Optical Remote Sensing, G. Asrar (Ed.) John Wiley & Sons
Liang, S. Quantitative Remote Sensing of Land Surfaces, John Wiley & SonsCh2: atmospheric radiative transfer modelingCh6: atmospheric correction methods
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Thank you !