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 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 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 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:

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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.