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VIIRS True Color Atmospheric Correction Updates

VIIRS True Color Atmospheric Correction Updates. Steve Miller 14 June 2012. Overview. VIIRS natural color processing commenced shortly after receipt of first-light data.

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VIIRS True Color Atmospheric Correction Updates

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  1. VIIRS True Color Atmospheric Correction Updates Steve Miller 14 June 2012

  2. 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.

  3. Modifications raysa(MODIS): 0.142865, 0.0801539, 0.0492007 raysa(VIIRS): 0.124679, 0.0797469, 0.0396954 aoz(MODIS): 0.015816, 0.09338, 0.056965 aoz(VIIRS): 0.0244511, 0.09338, 0.04604 awv(MODIS): 0.0, 0.0008, 0.003539 awv(VIIRS): 0.0, 0.0008, 0.00422421 ao2(MODIS): 0.0, 0.0, 0.0 ao2(VIIRS): 0.0, 0.0, 0.0 Coefficient Changes: Bands(MODIS): 3,4,1 (466nm, 554nm, 646nm) Bands(VIIRS): 3,4,5 (488nm, 555nm,672nm) F_sun(MODIS): 202.3, 186.0, 160.2 F_sun (VIIRS): 194.142, 185.930, 151.538 ray_taus(MODIS): 0.189789, 0.09490, 0.0492007 ray_taus(VIIRS): 0.159419, 0.09420, 0.04532 New Rayleigh Look-Up Tables: ftp://ftp.cira.colostate.edu/ftp/Miller/NRL/VIIRS_Rayleigh 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).

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  5. California Coastal Blooms OLD NEW

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  7. 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.

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