Refinement of MODIS Atmospheric Correction Algorithm Menghua Wang

Refinement of MODIS Atmospheric Correction Algorithm 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 Ocean Color Research Team Meeting April 11 -13, 2006, Hyatt Regency Newport, Rhode Island 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). Ø 2. Wang, M. and W. Shi, “Cloud masking for ocean color data processing in the coastal regions, ” IEEE Trans. Geosci. Remote Sens. (Accepted). Status: Developed cloud masking using MODIS SWIR bands (1240/1640/2130 nm). Scheme can be easily implemented into the MODIS data processing system. Ø 3. Developed schemes to identify cases for the strongly absorbing aerosols and turbid waters with the MODIS SWIR and visible data. Status: A poster is presented in this meeting. Work is in progress. Ø 4. Atmospheric correction using the MODIS SWIR bands. Status: This presentation. Work is in progress. Ø 5. Deriving the MODIS high spatial resolution ocean color data. Status: This presentation. Work is in progress. Menghua Wang, NOAA/NESDIS/ORA

Cloud Masking in Coastal Regions 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 in 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: SWIR Bands · · At the short wave IR (SWIR) wavelengths (>~1000 nm), ocean water has much strongly absorption and ocean contributions are significantly less. Thus, atmospheric correction can be carried out for coastal regions without using the bio-optical model. Water absorption for 869 nm, 1240 nm, 1640 nm, and 2130 nm are 5 m-1, 88 m-1, 498 m-1, and 2200 m-1, respectively. Results from simulations were presented in the Hawaii Ocean Science Meeting in Feb. of 2004. Examples using the MODIS Aqua 1240 and 2130 nm data to derive the ocean color products are provided. Ø We use the SWIR band (1240 nm) for the cloud masking. This is necessary for coastal region waters. Menghua Wang, NOAA/NESDIS/ORA

Water Absorption 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 MODIS 16 bands). Ø Aerosol optical property data (scattering phase function, single scattering albedo, extinction coefficients) for the SWIR bands (12 models & 16 bands). Ø The vector aerosol lookup tables (including the polarization effects) (12 aerosol models) for the SWIR bands, and for the MODIS high-spatial resolution bands. Ø 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 Aqua-MODIS 15 bands: 412, 443, 469, 488, 531, 555, 645, 667, 678, 748, 859, 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 We will use the MOBY in situ measurements for vicarious calibration. Menghua Wang, NOAA/NESDIS/ORA

Initial Results We compare the current MODIS results (downloaded directly from Web) and results from algorithm using SWIR bands. Normalized water-leaving radiances are derived for 412, 443, 469, 488, 531, 555, 645, 667, 678, 748, 859, and 869 nm. High spatial resolution products are derived for n. Lw(469) and n. Lw(555) (0. 5 km) and n. Lw(645) and n. Lw(859) (0. 25 km). Menghua Wang, NOAA/NESDIS/ORA

Chlorophyll-a (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Absorbing Aerosols Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

n. Lw(443) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Absorbing Aerosols Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

n. Lw(531) (2004096. 1820) Standard Processing (748, 869 nm) Menghua Wang, NOAA/NESDIS/ORA New Processing (1240, 2130 nm) April 6, 2004

Noise Effects: Chl-a (2004096. 1820) New Processing (SWIR 1 km) Menghua Wang, NOAA/NESDIS/ORA New Processing (SWIR 3 km) April 6, 2004

Noise Effects: n. Lw(531) (2004096. 1820) New Processing (SWIR: 1 km) Menghua Wang, NOAA/NESDIS/ORA New Processing (SWIR: 3 km) April 6, 2004

Ocean NIR Contributions (SWIR: 3 km) n. Lw(748) Menghua Wang, NOAA/NESDIS/ORA n. Lw(869) April 6, 2004

Outer Banks Outside of Outer Banks Histogram n. Lw(443) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

Outer Banks Outside of Outer Banks Histogram n. Lw(488) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

Outer Banks Outside of Outer Banks Histogram n. Lw(531) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

Histogram Chl-a in Outer Banks (2004096. 1820) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA Standard Processing (748, 869 nm) April 6, 2004

MODIS High Spatial Resolution Measurements Lt(645) (0. 25 km) Menghua Wang, NOAA/NESDIS/ORA Lt(645) (0. 25 km)

High Spatial Resolution Product n. Lw(645) (1 km, SWIR: 1 km) Chesapeake Bay Menghua Wang, NOAA/NESDIS/ORA n. Lw(645) (0. 25 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(555) (1 km, SWIR: 1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(555) (0. 5 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(469) (1 km, SWIR: 1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(469) (0. 5 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(645) (1 km, SWIR: 1 km) Outer Banks Menghua Wang, NOAA/NESDIS/ORA n. Lw(645) (0. 25 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(555) (1 km, SWIR: 1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(555) (0. 5 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(469) (1 km, SWIR: 1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(469) (0. 5 km, SWIR: 0. 5 km)

High Spatial Resolution Product n. Lw(859) (0. 5 km, SWIR: 0. 5 km) Menghua Wang, NOAA/NESDIS/ORA

High Spatial Resolution Product n. Lw(859) (0. 25 km, SWIR: 0. 5 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(859) (0. 25 km, SWIR: 0. 5 km)

n. Lw(645) Ocean Spectrum from Visible to NIR for Various Ocean Waters E D B A C Menghua Wang, NOAA/NESDIS/ORA

Conclusions 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 SWIR bands can be used for atmospheric correction over the turbid waters. No ocean model is needed! Ø For turbid waters, the Red-NIR n. Lw contributions are significant and can be useful to derive ocean properties in coastal regions. Ø To obtain high quality ocean color products, sensor with high (adequate) SNR values is crucial. Ø Future ocean color sensor needs to include wavelengths > ~1000 nm with high SNR values. Ø Future works: Calibration/Validation, Dealing with absorbing aerosols, some other details. Menghua Wang, NOAA/NESDIS/ORA

Some Backups Menghua Wang, NOAA/NESDIS/ORA

High Spatial Resolution Product (SWIR 3 km) n. Lw(645) (1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(645) (0. 25 km)

High Spatial Resolution Product (SWIR 3 km) n. Lw(555) (1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(555) (0. 5 km)

High Spatial Resolution Product (SWIR 3 km) n. Lw(645) (1 km) Menghua Wang, NOAA/NESDIS/ORA n. Lw(645) (0. 25 km)

Chesapeake Bay Outside of Chesapeake Bay Histogram n. Lw(443) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

Chesapeake Bay Outside of Chesapeake Bay Histogram n. Lw(488) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004

Chesapeake Bay Outside of Chesapeake Bay Histogram n. Lw(531) (2004096. 1820) Standard Processing (748, 869 nm) New Processing (1240, 2130 nm) Menghua Wang, NOAA/NESDIS/ORA April 6, 2004