1. Global Climatology of Aerosol Optical Depth
Aaron van Donkelaar, Randall V. Martin: Dalhousie University Ralph Kahn, Robert Levy: NASA Goddard
CAFC Meeting
1 February 2010

2. Average Aerosol Optical Depth (τ)
Mean τ at 0.1º x 0.1º
MODIS τ
1-2 days for global coverage
Requires assumptions about surface reflectivity
MODIS
MISR τ
6-9 days for global coverage
Simultaneous surface reflectance and aerosol retrieval
MISR
τ [unitless]

3. Exclude Retrievals Where Bias > 0.1 or 20%
July
MODIS
MISR
9 surface types, defined by monthly mean surface albedo ratios,
evaluation against AERONET AOD

4. Ground-Based PM2.5 Data Useful for Indirect AOD Validation
Annual Mean PM2.5 ( )
PM2.5 [μg/m3]

5. Combining MODIS & MISR Improves Agreement
0.3
0.25
0.2
0.15
0.1
0.05
Combined
MODIS/MISR
r = 0.63 (vs. in-situ PM2.5)
τ [unitless]
MODIS
r = 0.40
(vs. in-situ PM2.5)
MISR
r = 0.54
(vs. in-situ PM2.5)
r=0.45 for a simple average

6. Mean AOD (2001-2006) from MODIS and MISR
Spatial comparison vs AERONET
coincident: r=0.97, slope=1.02, 226 sites
non-coincident: r=0.75, slope=0.91, 258 sites