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2003
Earth Feature Story
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Sacramento
in 1990
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Sacramento
in 2000
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Difference
between 1990 - 2000
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Landsat Images of Sacramento: 1990, 2000, and Change over the
Decade
Landsat images of the Sacramento metropolitan area for July,
1990, July 2000, and an image showing the change that occurred
during the 1990s. Vegetation appears green, water looks blue,
and built up land is depicted as purple. The map of urban land
in 1990 is shown in yellow in the last panel, while new urban
growth from 1990-2000 is in orange. Credit:
Annemarie Schneider/NASA Landsat |
Special: NASA
SATELLITES WATCH WORLD'S CITIES GROW
Researchers
used NASA's Landsat satellite to measure and analyze urban growth
among a global cross-section of 30 mid-sized cities during the 1990s,
according to a two-part study presented at the Fall American Geophysical
Union Meeting in San Francisco.
Preliminary
results from Boston University research assistant and lead author
of the NASA-funded study, Annemarie Schneider, show that some cities
in the sample, including Atlanta, Georgia, Calgary, Canada, and
Curitiba, Brazil, grew in area by as much as 25 percent from 1990
to 2000. More importantly, this kind of global satellite-derived
analysis allows researchers to compare areas and determine spatial
trends in how cities have developed.
Also,
leading up to these findings, an early phase of this work used two
other satellites combined with population data to provide an up-to-date
assessment of urbanized land across the planet. This is important
because until now, climate modelers and others have relied on outdated
digital data of urban areas dating back to the 1960s.
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Hi
Res image
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Urban Land Cover, Northeast Corridor, United States
Researchers fused together information from NASA's Moderate
Resolution Imaging Spectroradiometer (MODIS) aboard the Terra
satellite, with the Defense Meteorological Satellite Program's
(DMSP)
nighttime lights imagery and population density data from
2001 to attain this representation of urban land cover along
the Northeast Corridor of the United States. Credit: Annemarie
Schneider, Boston University |
"Cities
such as Johannesburg and Shanghai have grown extensively, and we
need maps that reflect this," Schneider said. "These maps
will not only be useful to scientists studying energy transfer,
hydrology and climate interactions, but to social scientists trying
to understand the land impacts of population and economic activity
at a global scale."
To
obtain a complete assessment of global urban areas, Schneider combined
data from NASA's Moderate Resolution Imaging Spectroradiometer (MODIS)
aboard the Terra satellite, with the Defense Meteorological Satellite
Program's (DMSP) nighttime lights imagery and population density
data from 2001.
Each
data source has its advantages and disadvantages. For example, the
MODIS imagery provides coarse 1 kilometer (0.6 miles) resolution
data of the Earth, but has trouble distinguishing between urban
areas and barren landscapes. Meanwhile, the DMSP nighttime lights
data capture lit areas globally, but distributions of light do not
represent built environments or patterns of settlement. Schneider
compensated for inadequacies in each data source by fusing information
from all three.
Schneider's study provides a current global record of urbanization,
including growth in places like Africa that haven't been mapped
for many years. While scientists have improved their understanding
of local impacts of urbanization, including air pollution, urban
heat islands, vegetation changes, and modified rainfall patterns,
little is known about the cumulative impacts of cities on larger
regional and global climates. In order to create global climate
models that include the effects of city landscapes, scientists need
current assessments that locate and monitor urban areas globally.
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Calgary in 1990
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Calgary in 2000
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Difference
between 1990 - 2000
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Landsat Images of Calgary, Canada: 1990, 2000, and Change over
the Decade
Caption: Landsat images of the Calgary, Canada metropolitan
area for July, 1990, July 2000, and an image showing the change
that occurred during the 1990s. Vegetation appears green, water
looks blue, and built up land is depicted as purple. The map
of urban land in 1990 is shown in yellow in the last panel,
while new urban growth from 1990-2000 is in orange. Credit:
Annemarie Schneider/NASA Landsat |
This
is the first time MODIS data has been used to assess cities globally.
An article describing Schneider's technique for mapping urban areas
appears in the December issue of Photogrammetric Engineering and
Remote Sensing.
The
second phase of this study used 30 meter resolution Landsat imagery
during the 1990s to analyze growth patterns of 30 mid-sized cities
with populations between 1 and 5 million. Mid-sized cities were
chosen over mega-cities because smaller cities are growing at similarly
rapid rates, and there are many more mid-sized cities than mega-cities.
Cumulatively, mid-sized cities may potentially have a greater impact
on climate than mega-cities. Mid-sized U.S. cities included Sacramento,
Phoenix, Baltimore, Boston and Atlanta, with global cities from
Mexico, Brazil, Egypt, Turkey, India, China, the European Union,
Australia and more.
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Chengdu in 1990
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Chengdu
in 2000
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Difference
between 1990 - 2000
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Landsat
Images of Chengdu, China: 1990, 2000, and Change over the Decade
Landsat images of the Chengdu, China metropolitan area for July,
1990, July 2000, and an image showing the change that occurred
during the 1990s. Vegetation appears green, water looks blue,
and built up land is depicted as purple. The map of urban land
in 1990 is shown in yellow in the last panel, while new urban
growth from 1990-2000 is shown in orange. Credit: Annemarie
Schneider/NASA Landsat
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When
the cities were compared, three common spatial patterns became clear.
First, land developments have formed in clusters outside the city.
While fairly common in the U.S., Schneider noticed this trend in
large cities of China and India as well. Second, there are a number
of cities where growth has occurred along roads leading out of the
city. This trend poses challenges both to city managers and governments
who must provide water, sewage, adequate housing, schools and health
care services to dispersed people, and to the citizens, who face
increasingly difficult commutes. Finally, Schneider found scattered,
patchy development around cities, with less structure than the first
two trends. This is the first time actual data have been used to
confirm theories made by urban researchers during the last century.
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City
Samples
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Sample of Cities Used in Study of Urban Change in Mid-sized
Global Cities During 1990s
Caption: The metropolitan areas chosen for analysis (in red),
were selected randomly from a global sample of cities with populations
between 1 and 5 million people. Credit: Annemarie Schneider/Boston
University |
The
mission of NASA's Earth Science Enterprise is to develop a scientific
understanding of the Earth System and its response to natural or
human-induced changes to enable improved prediction capability for
climate, weather, and natural hazards.
For
more information, please see: http://duckwater.bu.edu/urban
Contacts:
Krishna Ramanujan
Goddard Space Flight Center, Greenbelt, Md.
(Phone: 607/273-2561)
Ann
Marie Menting
Boston University
(Phone: 617-358-1240)
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