Atmospheric Correction using the MODIS SWIR Bands 1240
Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm) Menghua Wang (PI, NASA NNG 05 HL 35 I) NOAA/NESDIS/ORA Camp Springs, MD 20746, USA Support from: Wei Shi UMBC, NOAA/NESDIS/ORA Camp Springs, MD 20746, USA The MODIS Science Team Meeting January 4 -6, 2006, Radisson Plaza Lord Baltimore Hotel, Maryland Menghua Wang, NOAA/NESDIS/ORA
Status of the Algorithm Modifications and Refinements ü 1. Wang, M. and W. Shi, “Estimation of ocean contribution at the MODIS nearinfrared wavelengths along the east coast of the U. S. : Two case studies, ” Geophys. Res. Lett. , 32, L 13606, doi: 10. 1029/2005 GL 022917 (2005). ü 2. Wang, M. , “A refinement for the Rayleigh radiance computation with variation of the atmospheric pressure, ” Int. J. Remote Sens. (In press). Status: Implemented into the MODIS/Sea. Wi. FS data processing. ü 3. Wang, M. , “Effects of ocean surface reflectance variation with solar elevation on normalized water-leaving radiance, ” App. Opt. (In press). Status: Implemented into the MODIS/Sea. Wi. FS data processing. Ø 4. Wang, M. and W. Shi, “Cloud masking for ocean color data processing in the coastal regions, ” IEEE Trans. Geosci. Remote Sens. (Submitted). Status: Developed cloud masking using MODIS SWIR bands (1240/1640/2130 nm). Scheme can be easily implemented into the MODIS data processing system. Ø 5. Developed schemes using idea of Wang and Gordon (1994) to identify cases for the strongly absorbing aerosols and turbid waters with the MODIS data. Status: A poster is presented in this meeting. Work is in progress. Ø 6. Atmospheric correction using the MODIS SWIR bands. Status: This presentation. Work is in progress. Menghua Wang, NOAA/NESDIS/ORA
Atmospheric Correction MODIS and Sea. Wi. FS algorithm (Gordon and Wang 1994) Ø Ø w is the desired quantity in ocean color remote sensing. T g is the sun glint contribution—avoided/masked/corrected. T wc is the whitecap reflectance—computed from wind speed. r is the scattering from molecules—computed using the Rayleigh lookup tables (atmospheric pressure dependence). Ø A = a + ra is the aerosol and Rayleigh-aerosol contributions —estimated using aerosol models. Ø For Case-1 waters at the open ocean, w is usually negligible at 750 & 865 nm. A can be estimated using these two NIR bands. Ocean is usually not black at NIR for the coastal regions. Gordon, H. R. and M. Wang, “Retrieval of water-leaving radiance and aerosol optical thickness over the oceans with Sea. Wi. FS: A preliminary algorithm, ” Appl. Opt. , 33, 443 -452, 1994. Menghua Wang, NOAA/NESDIS/ORA
Atmospheric Correction: Longer NIR · · · In general, to effect the atmospheric correction operationally using the NIR bands at 748 and 869 nm, or using the spectral optimization with measurements from 412 -865 nm, Case-2 biooptical model that has strongly regional dependence is needed. At the longer NIR wavelengths (>~1000 nm), ocean water is much strongly absorbing and ocean contributions are significant less. Thus, atmospheric correction may be carried out at the coastal regions without using the bio-optical model. Examples using the MODIS Aqua 1240 and 2130 nm data to derive the ocean color products. Ø We use the longer NIR (2130 nm) for the cloud masking. This is necessary for the coastal region waters. Menghua Wang, NOAA/NESDIS/ORA
Water Absorption Menghua Wang, NOAA/NESDIS/ORA
Water Absorption Relative to 865 nm Black ocean at the longer NIR bands: Absorption at the longer NIR bands is at least an order larger than that at the 865 nm Menghua Wang, NOAA/NESDIS/ORA
The Rayleigh-Corrected TOA Reflectance 748 nm 869 nm 1240 nm 1640 nm Rayleigh-Removed MODIS Terra Granule: 20040711515 (March 11, 2004) Menghua Wang, NOAA/NESDIS/ORA
Aerosol Single-Scattering Epsilon (l 0 = 865 nm) Menghua Wang, NOAA/NESDIS/ORA
Aerosol Single-Scattering Epsilon (l 0 = 2130 nm) Menghua Wang, NOAA/NESDIS/ORA
Data Processing Using the SWIR Bands Software Modifications: Ø Atmospheric correction package has been significantly modified based on Sea. DAS 4. 6. Ø Data structure and format of aerosol lookup tables and diffuse transmittance tables have been changed. Ø With these changes, it is flexible now to run with different aerosol models (e. g. , absorbing aerosols) and with various band combinations for atmospheric correction. Lookup Tables Generation and Implementation: Ø Rayleigh lookup tables for the SWIR bands (for all MODIS 16 bands). Ø Aerosol optical property data (scattering phase function, single scattering albedo, extinction coefficients) for the SWIR bands (12 models). Ø Aerosol radiance lookup tables (12 aerosol models) for the SWIR bands. Table structures are completely changed (different from the current ones). Data Processing: Ø Regenerated MODIS L 1 B data including all SWIR band data (for Sea. DAS). Ø Developed cloud masking using the MODIS 1240/1640/2130 nm band. Ø For MODIS Aqua, atmospheric correction can be operated using 1240/2130 bands, 869/1240 bands, and 869/2130 bands. Ø Current 8 bands: 412, 443, 488, 531, 551, 869, 1240, and 2130 nm. Menghua Wang, NOAA/NESDIS/ORA
We have carried out vicarious calibration using a MOBY scene from the standard processing…… Vicarious Gains Menghua Wang, NOAA/NESDIS/ORA
Initial Results We compare the current MODIS results (downloaded directly from Web) and results from algorithm using SWIR bands. Menghua Wang, NOAA/NESDIS/ORA
Chlorophyll-a (2004071. 1825) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) March 12, 2004
Chlorophyll-a (2004071. 1825) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) March 12, 2004
Three weeks late …… Chlorophyll-a (2004096. 1820) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) April 6, 2004
n. Lw(443) (2004071. 1825) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) March 12, 2004
n. Lw(531) (2004071. 1825) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) March 12, 2004
n. Lw(869) (2004071. 1825) n. Lw(869) New Processing (1240, 2130 nm) NIR ocean contributions Menghua Wang, NOAA/NESDIS/ORA March 12, 2004
Three weeks late …… n. Lw(443) (2004096. 1820) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) April 6, 2004
Three weeks late …… n. Lw(531) (2004096. 1820) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) April 6, 2004
n. Lw(869) (2004096. 1820) NIR ocean contributions New Processing (1240, 2130 nm) Three weeks late …… Menghua Wang, NOAA/NESDIS/ORA April 6, 2004
Outer Banks Outside of Outer Banks Histogram n. Lw(412) (2004071. 1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA March 12, 2004
Outer Banks Outside of Outer Banks Histogram n. Lw(443) (2004071. 1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA March 12, 2004
Outer Banks Outside of Outer Banks Histogram n. Lw(488) (2004071. 1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA March 12, 2004
Outer Banks Outside of Outer Banks Histogram n. Lw(531) (2004071. 1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA March 12, 2004
Outer Banks Chesapeake Bay Histogram n. Lw(869) (2004071. 1825) New Processing (1240, 2130 nm) Open Ocean Menghua Wang, NOAA/NESDIS/ORA SC Coast March 12, 2004
An example from the west coast … Chlorophyll-a (2004130. 2125) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) May 10, 2004
An example from the west coast … n. Lw(412) (2004130. 2125) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) May 10, 2004
An example from the west coast … n. Lw(488) (2004130. 2125) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) May 10, 2004
An example from the west coast … n. Lw(531) (2004130. 2125) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) May 10, 2004
n. Lw(869) (2004130. 2125) New Processing (1240, 2130 nm) NIR ocean contributions Menghua Wang, NOAA/NESDIS/ORA May 10, 2004
Effects of band noises: Chlorophyll-a (2004071. 1825) New Processing (1240, 2130 nm) Fixed Model: M 90 Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) Fixed Model: C 50 March 12, 2004
Effects of band noises: n. Lw(531) (2004071. 1825) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (869, 2130 nm) March 12, 2004
Effects of band noises: n. Lw(531) (2004071. 1825) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (869, 1240 nm) March 12, 2004
Standard 1240, 2130 nm Effects of Band Noise: Histogram n. Lw(531) (Open Ocean) (2004071. 1825) 869, 2130 nm 869, 1240 nm STD Value: Standard: 0. 0509 1240, 2130: 0. 1177 869, 2130: 0. 0704 869, 1240: 0. 0786 Menghua Wang, NOAA/NESDIS/ORA
Conclusions Ø It works! Ø For the turbid waters in coastal regions, ocean is not black at the NIR bands. This leads to underestimation of the sensor-measured water-leaving radiances with current Sea. Wi. FS/MODIS atmospheric correction algorithm. Ø Ocean is black for turbid waters at wavelengths >~1000 nm, e. g. , 1240 and 2130 nm. Thus, the longer NIR bands can be used for atmospheric correction over the turbid waters. No ocean model is needed! Ø Future ocean color sensor needs to include wavelengths > ~1000 nm with high SNR values. Menghua Wang, NOAA/NESDIS/ORA
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