Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm)...
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Transcript of Menghua Wang, NOAA/NESDIS/ORA Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm)...
Menghua Wang, NOAA/NESDIS/ORA
Atmospheric Correction using the MODIS SWIR Bands (1240 and 2130 nm)
Menghua Wang (PI, NASA NNG05HL35I)
NOAA/NESDIS/ORACamp 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
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
Menghua Wang, NOAA/NESDIS/ORA
Atmospheric Correction
w is the desired quantity in ocean color remote sensing.
Tg is the sun glint contribution—avoided/masked/corrected.
Twc 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.
t = ρr + ρ A + t ρ wc + Tρ g + tρ w, ρ = π L μ0 F0
MODIS and SeaWiFS algorithm (Gordon and Wang 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 412-865nm, 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.
Menghua Wang, NOAA/NESDIS/ORA
Water Absorption
10-4
10-3
10-2
10-1
100
101
102
103
400 600 800 1000 1200 1400 1600 1800 2000 2200
Hale & Querry (1973)Segelstein (1981)Kou et al. (1993)
Wavelength (nm)
(a)
1000 nm
865 nm
1240 nm
1640 nm
2130 nm
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
10-1
100
101
102
103
104
800 1000 1200 1400 1600 1800 2000 2200
Hale & Querry (1973)Segelstein (1981)Kou et al. (1993)
Wavelength (nm)
1000 nm
1240 nm
1640 nm
2130 nm
(b)
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
Menghua Wang, NOAA/NESDIS/ORA
Aerosol Single-Scattering Epsilon (0 = 865 nm)
0.6
0.7
0.8
0.9
1
2
300 420 540 660 780 900
O99M50M70M90M99C50C70C90C99T50T90T99ε
(, 0)
( )Wavelength nm
0 = 865 nm, θ
0 = 60o, θ = 45o, Δφ = 90o
(a)
Menghua Wang, NOAA/NESDIS/ORA
Aerosol Single-Scattering Epsilon (0 = 2130 nm)
1
10
300 500 700 900 1100 1300 1500 1700 1900 2100
O99 M50 M70 M90 M99 C50 C70 C90 C99 T50 T90 T99
( )Wavelength nm
0 = 2130 nm, θ
0 = 60
o, θ = 20
o, Δφ = 90
o
(d)
Menghua Wang, NOAA/NESDIS/ORA
Data Processing Using the SWIR BandsSoftware 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.
Menghua Wang, NOAA/NESDIS/ORA
Vicarious Gains
Wavelength (nm)
Gain= (1240, 2130)
Gain= (869, 2130)
Gain= (869, 1240)
412 0.975 0.973 0.969
443 0.980 0.979 0.969
488 0.970 0.971 0.969
531 0.978 0.978 0.970
551 0.960 0.960 0.966
869 0.976 0.976 0.976
1240 1.0 1.0 1.0
2130 1.0 1.0 1.0
= Derived from MOBY scene 2004039.2320.004
We have carried out vicarious calibration using a MOBY scene from the standard
processing……
Menghua Wang, NOAA/NESDIS/ORA
We compare the current MODIS results (downloaded directly from Web) and results
from algorithm using SWIR bands.
Initial Results
Menghua Wang, NOAA/NESDIS/ORA
Chlorophyll-a (2004071.1825)
New Processing (1240, 2130 nm)Standard Processing (748, 869 nm)
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
Chlorophyll-a (2004071.1825)
New Processing (1240, 2130 nm)Standard Processing (748, 869 nm)
March 12, 2004
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
Menghua Wang, NOAA/NESDIS/ORA
nLw(443) (2004071.1825)New Processing (1240, 2130 nm)Standard Processing (748, 869 nm)
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
nLw(531) (2004071.1825)New Processing (1240, 2130 nm)Standard Processing (748, 869 nm)
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
nLw(869) (2004071.18
25)
New Processing(1240, 2130 nm)
nLw(869)
March 12, 2004
NIR ocean contributions
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
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
Menghua Wang, NOAA/NESDIS/ORA
nLw(869) (2004096.18
20)
New Processing(1240, 2130 nm)
nLw(869)
April 6, 2004
Three weeks late ……
NIR ocean contributions
Menghua Wang, NOAA/NESDIS/ORA
HistogramnLw(412) (2004071.18
25)Standard Processing(748, 869 nm)
New Processing(1240, 2130 nm)
Outer Banks Outside of Outer Banks
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
HistogramnLw(443) (2004071.18
25)Standard Processing(748, 869 nm)
New Processing(1240, 2130 nm)
Outer Banks Outside of Outer Banks
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
HistogramnLw(488) (2004071.18
25)Standard Processing(748, 869 nm)
New Processing(1240, 2130 nm)
Outer Banks Outside of Outer Banks
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
HistogramnLw(531) (2004071.18
25)Standard Processing(748, 869 nm)
New Processing(1240, 2130 nm)
Outer Banks Outside of Outer Banks
March 12, 2004
Menghua Wang, NOAA/NESDIS/ORA
HistogramnLw(869) (2004071.18
25)
New Processing(1240, 2130 nm)
Open Ocean
Outer Banks Chesapeake Bay
SC Coast
March 12, 2004
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 …
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 …
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 …
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 …
Menghua Wang, NOAA/NESDIS/ORA
nLw(869) (2004130.21
25)
New Processing(1240, 2130 nm)
May 10, 2004
NIR ocean contributions
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:
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
Fixed Model: M90 Fixed Model: C50
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:
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)
Menghua Wang, NOAA/NESDIS/ORA
Effects of Band Noise:
HistogramnLw(531)(Open Ocean)
(2004071.1825)
Standard 1240, 2130 nm
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 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.