Spatial Variation Assessed By Satellite
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Figure 2. Trend of chemical b ext at (a) BLIS1 and (b) SOLA1. The whiskers and boxes indicate 90 th , 80 th , 20 th , and 10 th percentile of b ext for each year. Small bars indicate the median values. Linear regressions for the 90 th and 10 th percentile data are calculated and presented. Red lines indicate the current 90% and 50% standards for (a) regional and (b) sub-regional visibility. The mean natural background level is also indicated.
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Figure 2. Trend of chemical bext at (a) BLIS1 and (b) SOLA1. The whiskers and boxes indicate 90th, 80th, 20th, and 10th percentile of bext for each year. Small bars indicate the median values. Linear regressions for the 90 th and 10th percentile data are calculated and presented. Red lines indicate the current 90% and 50% standards for (a) regional and (b) sub-regional visibility. The mean natural background level is also indicated.
Spatial Variation Assessed By Satellite• AOD- column-total aerosol light extinction: AOD = ∫bext(dz) If all aerosol is in boundary layer AOD approximated by bext·L (L=boundary layer depth)•NASA MODIS AOD (Level II) data from Satellites Terra and Aqua•10 km 10 km resolution at nadir view• Twice daily scans during day time (about 11:00 AM and 1:00 PM• Less valid AOD data available in winter due to frequent cloudy skies over the Lake Tahoe basin• Spatial distribution of AOD is calculated based on valid AOD data points
Assumptions for surface/satellite comparability
• Spatial homogeneity across pixels and within mixed layers
• Cloudless sky• Temporal correspondence between surface and
satellite estimates• Constant aerosol extinction properties (e.g., size,
composition, and shape)
Domain of Study
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
• 11 11 points in the domain of interest• Surface chemical visibility measurements were made at BLIS and SOLA
Resourceshttp://modis-atmos.gsfc.nasa.gov/MOD04_L2/
acquiring.html
HDF Viewer
Matlab hdfread
120.0 W
40.0 N
0.05
0.1
0.15
0.2
0.25
0.3
(a)
120.4 W 120.2 W 120.0 W 119.8 W 119.6 W
38.6 N
38.8 N
39.0 N
39.2 N
39.4 N
39.6 N
0.05
0.1
0.15
0.2
0.25
0.3
(b)
AOD Data Interpolation
MODIS (Aqua Level 2) AOD data for (a) the western U.S. and (b) Lake Tahoe region on 6/27/2007. Blanks indicate missing or invalid pixels
Seasonal Variation of Data AvailabilityNumber of Valid Grid Points in 2008
0
2000
4000
6000
8000
1 2 3 4 5 6 7 8 9 10 11 12
Month in 2008
# of
Val
id G
rid P
oint
s
AOD versus Surface bext (Mm-1)
All concurrent data for BLIS from 2007 to 2009
0
20
40
60
80
100
120
140
0 0.1 0.2 0.3 0.4 0.5
Stratified AOD
Aer
osol
bex
t
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
How many % differs from BLIS?
• So BLIS represents a very large area (for July 2007)
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
Average July AOD
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
BLIS
SOLA
120.3 W
120.2 W
120.1 W
120.0 W
119.9 W
119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
2007
2008
2009
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
Average October AOD
BLIS
SOLA
120.3 W
120.2 W
120.1 W
120.0 W
119.9 W
119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
2007
2008
2009
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
0.1
0.15
0.2
0.25
0.3
BLISSOLA 120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N 39.0 N 39.1 N 39.2 N 39.3 N
0.1 0.2 0.3 0.4 0.5 0.6 0.7
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
11:00, 6/24/2007
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
11:00, 6/25/2007
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
13:00, 6/25/2007
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
11:00, 6/26/2007
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
11:00, 6/27/2007
BLIS
SOLA
120.3 W 120.2 W 120.1 W 120.0 W 119.9 W 119.8 W
38.9 N
39.0 N
39.1 N
39.2 N
39.3 N
13:00, 6/27/2007
Episodic Aerosol Optical Depth
AOD map during the Angora Fire event
Spatial Analysis suggests that:
1) background PM and bext levels are pretty uniform across the Tahoe basin, except during severe wildfire events,
2) influences such as traffic and residential wood combustion are confined in urban “neighborhoods” (sub-pixel), and
3) visibility within the basin would be well bounded by BLIS1 (background) and SOLA1 (maximum) measurements
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