VIIRS True Color Atmospheric Correction Updates Steve Miller 14 June 2012.
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Transcript of VIIRS True Color Atmospheric Correction Updates Steve Miller 14 June 2012.
VIIRS True Color Atmospheric Correction Updates
Steve Miller14 June 2012
Overview• VIIRS natural color processing commenced shortly after receipt of first-
light data.• To expedite initial product suite, the atmospheric corrections necessary
for high-quality true color imagery were adopted from the legacy MODIS processing.
• The MODIS Blue/Green/Red bands (466, 554, 646 nm) are slightly different than VIIRS (488, 555, 672 nm).
• Associated rayleigh optical depths are different, leading to erroneous corrections when applying the MODIS coefficients and tables to VIIRS data.
• Correct handling of VIIRS requires a re-calculation of the necessary components, including: Fo, tau_ray, tau_ozone, tau_oxygen, tau_watvap.
• Codes adapted from SEADAS software (Eric Vermote and Norman Kuring).
• Monochromatic calculation used here (no band weighting), with values for various properties interpolated linearly from the original SeaWiFS band values. Sufficient for qualitative imagery product.
Modifications
Bands(MODIS): 3,4,1 (466nm, 554nm, 646nm)Bands(VIIRS): 3,4,5 (488nm, 555nm,672nm)
F_sun(MODIS): 202.3, 186.0, 160.2F_sun (VIIRS): 194.142, 185.930, 151.538
ray_taus(MODIS): 0.189789, 0.09490, 0.0492007ray_taus(VIIRS): 0.159419, 0.09420, 0.04532
New Rayleigh Look-Up Tables:
ftp://ftp.cira.colostate.edu/ftp/Miller/NRL/VIIRS_Rayleigh
raysa(MODIS): 0.142865, 0.0801539, 0.0492007raysa(VIIRS): 0.124679, 0.0797469, 0.0396954
aoz(MODIS): 0.015816, 0.09338, 0.056965aoz(VIIRS): 0.0244511, 0.09338, 0.04604
awv(MODIS): 0.0, 0.0008, 0.003539awv(VIIRS): 0.0, 0.0008, 0.00422421
ao2(MODIS): 0.0, 0.0, 0.0ao2(VIIRS): 0.0, 0.0, 0.0
Implementing the simple coefficient and table modifications listed above will result in dramatic improvements to VIIRS true color image quality. The following slides show before/after corrections applied (must run in slide-show mode to toggle imagery).
Coefficient Changes:
OLDNEW
California Coastal Blooms
OLDNEW
OLDNEW
Next Steps
• Evaluate the stability and performance at various sites.
• Apply these new corrections to the VIIRS dust enhancement prototype.
• Develop an I-band true color product based on re-bin of M-bands to 375 m resolution using similar techniques as MODIS 250 m.