Transcript 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.
• 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
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
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
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).
NEW
OLD
California Coastal Blooms
NEW
OLD
NEW
OLD
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.