Image Processing Reference
In-Depth Information
Analytical Methods and Techniques
Study Area
We illustrate the use of ASTER and MODIS data for urban ecological analysis
using the Phoenix, Arizona metropolitan area. Phoenix was selected because it is
one of the fastest-growing conurbations in the United States, and is the focus of the
Central Arizona-Phoenix Long-Term Ecological Research Project (CAP LTER;
Grimm et al. 2000 ). This project has been the locus of significant remote sensing
investigation and characterization of the Phoenix urban/peri-urban area (Stefanov
2002 ; Jenerette et al. 2007 ; Stefanov et al. 2007 ) combined with ground truthing
and allied studies (Hope et al. 2003 ; Wentz et al. 2006 ).
The greater Phoenix metropolitan area is situated on an alluvial plain formed by
the Salt River and alluvial fans derived from the surrounding mountain ranges
(Nations and Stump 1996 ), at an elevation of 305 m in an arid environment that
averages less than 20 cm of annual precipitation. Mean monthly temperatures in the
region range from 12°C in January to 34°C in July. The area contains 300,000 ha
of highly productive farmland, and 3.2 million people (2000 US Census data) are
concentrated in an expanding metropolitan area. The growth of industry related to
World War II, the introduction of air conditioning, the rise of automobile traffic,
expanding tourism, and a growth-minded citizenry propelled Phoenix into the larg-
est population center of the American Southwest, converting it to an industrial,
commercial, and administrative hub and the fastest-growing metropolitan area in
the United States (Gammage 1999 ; Kupel 2003 ).
ASTER and MODIS Image Processing
The work presented here uses ASTER data for Phoenix, AZ acquired on
September 19, 2000. Scenes were obtained as “Level 2” atmospherically corrected
data products. Atmospheric correction for the visible, shortwave infrared, and
thermal infrared Level 2 products is accomplished using a radiative transfer model
and atmospheric parameters derived from the National Centers for Environmental
Prediction (NCEP) data (Abrams 2000 ). Two contiguous scenes were required to
provide coverage for the eastern Phoenix metropolitan area. The visible to near
infrared (VNIR) bands of each scene were georeferenced to the Universal
Transverse Mercator (UTM) coordinate system using nearest-neighbor resampling
and the pixel location grid incorporated into ASTER data. The two scenes were then
mosaiced to form a single contiguous dataset using a commercial image-processing
software package. No manipulation of the individual scene histograms was per-
formed as each was already calibrated to reflectance.
Appropriate subsets of the MODIS datasets listed in Table 12.1 were extracted
to match the ASTER data coverage for Phoenix. Each of these data products are
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