NAAPS simulations of atmospheric aerosols are validated by comparing the simulated
aerosol optical depth (AOD; upper-left image) with those retrieved daily by MODIS and
post-processed by NRL to level 3 (L3; top row, right image).
The calculation of the NAAPS AOD is discussed
here.
The comparison is made on a pixel-by-pixel basis with the pixels being 1 degree
square for both NAAPS and the NRL MODIS L3 AOD.
The MODIS AOD is available over most of the globe on a daily
basis but there are areas where no AOD is retrieved, due to cloud, land, sunglint,
and night.
Comparison is made only at the available pixels and only when the MODIS AOD pixel value
is within 12 hours of the time of the NAAPS simulation.
These valid data are shown in the center image of the top row.
The comparison is made as scatter plots with MODIS AOD on the abscissa and NAAPS
AOD on the ordinate.
When either the NAAPS or MODIS AOD values exceed the limits of axes, both are scaled
by 0.25 and then the point is plotted as a larger red asterisk.
To identify regional biases, the comparison is made on a number of subdomains, denoted
by the red boxes in the plot of the NAAPS AOD (upper right).
These are chosen to enclose aerosol types:
Those valid points not included in one of the subdomains are then plotted as `other'
so that unidentified or unexpected patterns and biases do not go unnoticed.
All valid points are plotted in the `globe' plot (lower-right).
The linear coefficient of correlation is calculated and displayed in each scatter plot
following the subdomain name and the number of valid pixels.
