1. Erin Robinson, Alan Pinkert June, 2010
Vertical Characterization of Aerosol over the U.S. - Aeronet, MODIS AOT
Erin Robinson, Alan Pinkert
June, 2010

2. Activities Begin comparing MODIS to Aeronet standard AOT
Comparing trends in Aeronet station patterns along similar latitudes

3. Varied Cursor Box Size and Statistic (GSFC)
.1 Deg x .1 deg
.5 Deg x .5 deg
1 Deg x 1 deg
Need to find MODIS cursor box size and statistical aggregation that most closely approximated Aeronet
MODIS is a grid dataset and Aeronet is a point dataset.
Chose to vary the cursor box from .1 deg x .1 deg (resolution of MODIS) to 2 deg x 2deg
Varied statistical aggregation for 5th percentile, 60th percentile and 95th percentile.

4. Results:
We saw that some sites had no correlation between MODIS and Aeronet.
For the sites that did have correlation – we saw no major variation between .1 and 1 deg.
Others who have done MODIS-Aeronet comparisons chose a .5 deg box
Since we didn’t see any major variation, we chose a .5 deg box for our analysis.

5. Seasonal Comparison – Annual
R2 (Blue low; Red ~1)
Slope (yellow =1; Red > 1)
Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON).
Annual correlation smears the systematic differences that MODIS has during different seasons
Compared the R2 value for how ‘repeatable’ the measurement was
The slope of the scatter plot indicates how close the Modis measurement is to Aeronet standard overall
Good correlation on East and NW
MODIS approxmates most sites well (yellow paddles (slope = .8-1); Overestimates in west

6. Seasonal Comparison – Winter
R2 (Blue low; Red ~1)
Slope (yellow =1; Red > 1)
Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON).
Annual correlation smears the systematic differences that MODIS has during different seasons
Low correlation at all sites
MODIS approxmates most sites well (yellow paddles (slope = .8-1); Overestimates in west

7. Seasonal Comparison – Summer
R2 (Blue low; Red ~1)
Slope (yellow =1; Red > 1)
Over the U.S. we looked at the correlation and slope for annual and seasonal comparison the Winter (DJF), Spring (MAM), Summer (JJA) and Fall (SON).
Annual correlation smears the systematic differences that MODIS has during different seasons
Good correlation on East and NW
MODIS approxmates most sites well; Overestimates in west
The Walker Branch site shows good correlation, but slope is underestimated –
this could be a systematic error that could be fixed

8. Troposheric Aerosol
Aerosol in the troposphere at a constant latitude has the same composition
Looking at Aeronet cycle views over for sites in a similar latitude to determine if there are any consistent patters
Patterns between multiple sites mean that the aerosol is likely in troposphere and not on the surface.

9. Southwest U.S.
January to April Peak