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Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm) Menghua Wang (PI, NASA NNG05HL35I) NOAA/NESDIS/ORA Camp.

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Presentation on theme: "Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm) Menghua Wang (PI, NASA NNG05HL35I) NOAA/NESDIS/ORA Camp."— Presentation transcript:

1 Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm) Menghua Wang (PI, NASA NNG05HL35I) 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

2 Menghua Wang, NOAA/NESDIS/ORA 1. Wang, M. and W. Shi, “Estimation of ocean contribution at the MODIS near- infrared wavelengths along the east coast of the U.S.: Two case studies,” Geophys. Res. Lett., 32, L13606, doi:10.1029/2005GL022917 (2005). 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/SeaWiFS data processing. 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/SeaWiFS data processing.  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.  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.  6. Atmospheric correction using the MODIS SWIR bands. Status: This presentation. Work is in progress. Status of the Algorithm Modifications and Refinements

3 Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction   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).   A =  a +  ra is the aerosol and Rayleigh-aerosol contributions —estimated using aerosol models.  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 SeaWiFS: A preliminary algorithm,” Appl. Opt., 33, 443-452, 1994. MODIS and SeaWiFS algorithm (Gordon and Wang 1994)

4 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 412-865nm, Case-2 bio- optical 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.  We use the longer NIR (2130 nm) for the cloud masking. This is necessary for the coastal region waters.

5 Menghua Wang, NOAA/NESDIS/ORA Water Absorption

6 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

7 Menghua Wang, NOAA/NESDIS/ORA 748 nm 1240 nm 869 nm 1640 nm MODIS Terra Granule:20040711515 (March 11, 2004) The Rayleigh-Corrected TOA Reflectance Rayleigh-Removed

8 Menghua Wang, NOAA/NESDIS/ORA Aerosol Single-Scattering Epsilon ( 0 = 865 nm)

9 Menghua Wang, NOAA/NESDIS/ORA Aerosol Single-Scattering Epsilon ( 0 = 2130 nm)

10 Menghua Wang, NOAA/NESDIS/ORA Data Processing Using the SWIR Bands Software Modifications:  Atmospheric correction package has been significantly modified based on SeaDAS 4.6.  Data structure and format of aerosol lookup tables and diffuse transmittance tables have been changed.  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:  Rayleigh lookup tables for the SWIR bands (for all MODIS 16 bands).  Aerosol optical property data (scattering phase function, single scattering albedo, extinction coefficients) for the SWIR bands (12 models).  Aerosol radiance lookup tables (12 aerosol models) for the SWIR bands. Table structures are completely changed (different from the current ones). Data Processing:  Regenerated MODIS L1B data including all SWIR band data (for SeaDAS).  Developed cloud masking using the MODIS 1240/1640/2130 nm band.  For MODIS Aqua, atmospheric correction can be operated using 1240/2130 bands, 869/1240 bands, and 869/2130 bands.  Current 8 bands: 412, 443, 488, 531, 551, 869, 1240, and 2130 nm.

11 Menghua Wang, NOAA/NESDIS/ORA Vicarious Gains We have carried out vicarious calibration using a MOBY scene from the standard processing……

12 Menghua Wang, NOAA/NESDIS/ORA We compare the current MODIS results (downloaded directly from Web) and results from algorithm using SWIR bands. Initial Results

13 Menghua Wang, NOAA/NESDIS/ORA Chlorophyll-a (2004071.1825) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) March 12, 2004

14 Menghua Wang, NOAA/NESDIS/ORA Chlorophyll-a (2004071.1825) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) March 12, 2004

15 Menghua Wang, NOAA/NESDIS/ORA Chlorophyll-a (2004096.1820) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) Three weeks late …… April 6, 2004

16 Menghua Wang, NOAA/NESDIS/ORA nLw(443) (2004071.1825) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) March 12, 2004

17 Menghua Wang, NOAA/NESDIS/ORA nLw(531) (2004071.1825) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) March 12, 2004

18 Menghua Wang, NOAA/NESDIS/ORA nLw(869) (2004071.1825) New Processing (1240, 2130 nm) nLw(869) March 12, 2004 NIR ocean contributions

19 Menghua Wang, NOAA/NESDIS/ORA nLw(443) (2004096.1820) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) Three weeks late …… April 6, 2004

20 Menghua Wang, NOAA/NESDIS/ORA nLw(531) (2004096.1820) New Processing (1240, 2130 nm)Standard Processing (748, 869 nm) Three weeks late …… April 6, 2004

21 Menghua Wang, NOAA/NESDIS/ORA nLw(869) (2004096.1820) New Processing (1240, 2130 nm) nLw(869) April 6, 2004 Three weeks late …… NIR ocean contributions

22 Menghua Wang, NOAA/NESDIS/ORA Histogram nLw(412) (2004071.1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Outer BanksOutside of Outer Banks March 12, 2004

23 Menghua Wang, NOAA/NESDIS/ORA Histogram nLw(443) (2004071.1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Outer BanksOutside of Outer Banks March 12, 2004

24 Menghua Wang, NOAA/NESDIS/ORA Histogram nLw(488) (2004071.1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Outer BanksOutside of Outer Banks March 12, 2004

25 Menghua Wang, NOAA/NESDIS/ORA Histogram nLw(531) (2004071.1825) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Outer BanksOutside of Outer Banks March 12, 2004

26 Menghua Wang, NOAA/NESDIS/ORA Histogram nLw(869) (2004071.1825) New Processing (1240, 2130 nm) Open Ocean Outer Banks Chesapeake Bay SC Coast March 12, 2004

27 Menghua Wang, NOAA/NESDIS/ORA Chlorophyll-a (2004130.2125) Standard Processing (748, 869 nm)New Processing (1240, 2130 nm) May 10, 2004 An example from the west coast …

28 Menghua Wang, NOAA/NESDIS/ORA nLw(412) (2004130.2125) Standard Processing (748, 869 nm)New Processing (1240, 2130 nm) May 10, 2004 An example from the west coast …

29 Menghua Wang, NOAA/NESDIS/ORA nLw(488) (2004130.2125) Standard Processing (748, 869 nm)New Processing (1240, 2130 nm) May 10, 2004 An example from the west coast …

30 Menghua Wang, NOAA/NESDIS/ORA nLw(531) (2004130.2125) Standard Processing (748, 869 nm)New Processing (1240, 2130 nm) May 10, 2004 An example from the west coast …

31 Menghua Wang, NOAA/NESDIS/ORA nLw(869) (2004130.2125) New Processing (1240, 2130 nm) May 10, 2004 NIR ocean contributions

32 Menghua Wang, NOAA/NESDIS/ORA Chlorophyll-a (2004071.1825) New Processing (1240, 2130 nm) March 12, 2004 New Processing (1240, 2130 nm) Effects of band noises: Fixed Model: M90Fixed Model: C50

33 Menghua Wang, NOAA/NESDIS/ORA nLw(531) (2004071.1825) New Processing (869, 2130 nm) March 12, 2004 New Processing (1240, 2130 nm) Effects of band noises:

34 Menghua Wang, NOAA/NESDIS/ORA nLw(531) (2004071.1825) New Processing (869, 1240 nm) March 12, 2004 Effects of band noises: Standard Processing (748, 869 nm)

35 Menghua Wang, NOAA/NESDIS/ORA Effects of Band Noise: Histogram nLw(531) (Open Ocean) (2004071.1825) Standard1240, 2130 nm 869, 2130 nm869, 1240 nm STD Value: Standard: 0.0509 1240, 2130: 0.1177 869, 2130: 0.0704 869, 1240: 0.0786

36 Menghua Wang, NOAA/NESDIS/ORA Conclusions  It works!  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 SeaWiFS/MODIS atmospheric correction algorithm.  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!  Future ocean color sensor needs to include wavelengths > ~1000 nm with high SNR values.


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