| December 12, 2003
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until now, climate modelers and others have relied on outdated digital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.
“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.
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.
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.
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 |
|
Sacramento in 1990
Sacramento in 2000
Difference between 1990 - 2000
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
1990
High-Resolution Image
2000
High-Resolution Image
1990-2000
High-Resolution Image
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
High-Resolution
Image
Calgary in 1990
Calgary in 2000
Difference between 1990 - 2000
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
1990
High-Resolution Image
2000
High-Resolution Image
1990-2000
High-Resolution Image
Chengdu in 1990
Chengdu in 2000
Difference between 1990 - 2000
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
1990
High-Resolution Image
2000
High-Resolution Image
1990-2000
High-Resolution Image
Sample of Cities Used in Study of Urban Change in Mid-sized Global
Cities During 1990s
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
High-Resolution Image
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