Image Processing Reference
In-Depth Information
The MODIS sensors are similar to ASTER in that they
obtain spectral information in the visible through mid-
infrared wavelengths over 36 bands with a swath width of
2,300 km. However, the spatial resolution of MODIS data
is significantly lower and ranges from 250 m/pixel (two
visible bands), 500 m/pixel (five visible to shortwave
infrared bands), and 1,000 m/pixel (29 visible, near infra-
red, shortwave infrared, and mid-infrared bands; Parkinson
and Greenstone
2000
). As both the Terra and Aqua satel-
lites are equipped with MODIS sensors, repeat coverage
over any given area of the Earth is acquired every 1-2
days. This makes MODIS data especially attractive for
fine-scale temporal monitoring of regional land surface
processes associated with urban centers (Schaaf et al.
2002
; Schneider et al.
2003
). In addition, the MODIS science team produces data
products useful for characterization and monitoring of regional-scale biophysical
and climatic variables in urban/peri-urban areas. The MODIS data products used
in the current study are listed in Table
12.1
, and they have been validated for sci-
entific use by the MODIS Science Team.
Surface temperatures from MODIS are calculated using paired day/night mea-
surements in seven thermal infrared bands and atmospheric profile data also derived
from MODIS (Wan and Li
1997
). Day and night surface temperature data are
important for understanding of urban climatology and urban heat island effects
(Brazel et al.
2000
; Stefanov and Brazel
2007
; Voogt and Oke
2003
). The acquisi-
tion times for temperature data are 11:00/22:54 (day/night). The normalized differ-
ence vegetation index (NDVI) produced every 16 days provides a gross measure of
relative photosynthetically active vegetation abundance per pixel (Botkin et al.
1984
; Tucker
1979
). The Leaf Area Index (LAI) and fPAR (fraction of photosyn-
thetically active radiation) are both calculated on an 8-day basis with the highest
value during that period recorded as the pixel value (Running et al.
2000
). These
parameters are measurements of the capacity of the biophysical landscape to utilize
incoming radiation for photosynthesis (LAI) and the amount of radiation so utilized
(fPAR; Smith
1980
). Albedo is the ratio of radiation reflected from the ground
in addition to
traditional
platform- and
radiometrically-
corrected data,
the EOS science
teams provide a
variety of science
data products
including albedo,
vegetation indices,
and surface
temperature
Table 12.1
MODIS biophysical datasets used for comparison with Phoenix landscape metrics
Data product
Time period
Days
Resolution (m)
Data description (units)
MOD11A1
19-September-00
1
1,000
Land surface
temperature (K)
MOD13A2
13-September-00 to
28-September-00
16
1,000
Normalized difference
vegetation index
(unitless)
MOD15A2
13-September-00 to
21-September-00
8
1,000
Leaf area index (%)
and fraction of
photosynthetically
active radiation (m
2
/m
2
)
MOD43B3
13-September-00 to
28-September-00
16
1,000
Albedo (unitless)
