Urban Growth
Seen from Space
Ask anyone who lives in D.C. or New York or Phoenix: urban growth is booming
and it's having profound effects on people's lives. Now research data confirms
it. Using sophisticated remote sensing systems, scientists have evidence
of significant changes to regional geography. At this year's annual meeting
of the American Association for the Advancement of Science in Washington,
D.C., researchers present findings about their study of wide scale urbanization.
While some of their work demonstrates common sense causes and effects from
growth, others provide startling evidence for heavy urban growth apparently
causing major changes to local weather and climate patterns.
ATLANTA SPREADS OUT AND
HEATS UP
|
|
|
True Color |
Thermal Day |
Thermal Night |
Images and Movies
It's official: in terms of annual take-offs and landings, Atlanta's Hartsfield
Airport is now the busiest in the world. But airport traffic is only one
of many urban growth signs in Georgia's cosmopolitan jewel. Burgeoned by
a robust economy, "Hot-Lanta" has seen phenomenal growth recently, from
soaring downtown high rises to sprawling suburbs and industrial parks. And
hot it is: the home of the Braves is so thick with asphalt and air conditioners
that it's become a "heat island", soaking up radiant energy during the day
and holding onto it at night. Data indicates that heavily developed parts
of the Atlanta metro remain warmer than surrounding areas, effectively trapping
heat like a sponge holds water.
Many of those localized heat sinks are centered around areas where growth
is greatest, especially along county borders, transportation routes, and
downtown. But besides bigger traffic jams, researchers say all this growth
is changing the region's climate. Heat rising from developed areas is spawning
thunderstorms. Notice how the storms in these weather images begin to coalesce
directly over the hottest parts of town. As the city grows, so grow the
thunderheads.
3D Heat Signature
Using a specially outfitted Lear Jet, NASA researchers collected thermal
data about the Atlanta metro area. As shown here, that aircraft data is
lined up with a larger image, taken from the orbiting Landsat 5 satellite.
The image starts in "natural" color and immediately transitions to a daytime
temperature reading, with white and red indicating highest temperatures,
respectively, and blues indicating cooler temperatures. Notice how the buildings
themselves help keep small areas cool, casting shadows across the pavement
and walls of surrounding structures. As the city rotates, the data fades
to a nighttime reading. Using the same color scale, you can see how much
heat remains locked in the developed areas of the city, a phenomena which
becomes instantly apparent as the picture zooms out again to show the long
stripe of data draped across the terrain.
|
|
|
Suburban true color |
Suburban day temperature |
Suburban night temperature |
|
|
|
Urban true color |
Urban day temperature |
Urban night temperature |
Images and Movies
These data were collected May 11 and 12, 1997. While daytime air temperatures
on that date were only about 80 degrees, surface temperatures reached as
much as 118 (F); nighttime air temperatures hovered between 50 and 55, but
due to the heat sink, surface temperatures hung on as high as 75 degrees.
Patterns of Urban Growth
|
|
|
1973 |
1979 |
1983 |
|
|
|
1987 |
1992 |
1997 |
Images and Movies
In the past 17 years, urban growth in Atlanta has spread and blossomed,
but not without dramatic changes to the surrounding area. Large patches
of crop land have given way to commercial and residential developments,
and industrialization along some of the main roadways have dramatically
altered the face of Georgia's largest city. In this visualization, red and
orange points indicate areas of highest urban growth. Researchers assembled
data from Landsat satellites in the early 70's to the late 90's and created
plots of growth over time, providing valuable context for more detailed
studies of air quality, climate changes, and urban planning. This series
of images, green and light blue spaces yield to ever spreading red and orange
points.
Cloud Formation
Atlanta's strong urban growth is being studied for a variety
of reasons. One of the most dramatic areas of study concerns the way intense
development may be affecting the region's climate. In the following animation,
we see the outlines of Atlanta and Hartsfield Airport; the tiny dot in
the lower left corner of Atlanta is the downtown skyline. As observed
by one of the Geostationary Operational Environmental Satellite (GOES),
clouds begin forming over the city and pick up strength and size as they
develop, moving east. Research suggests that as the city holds onto heat
at night, it creates a low pressure system, with hot air rising and cooler
surrounding air rushing in to replace it. That cooler air condenses and
forms thunderclouds. But now there's evidence suggesting the phenomenon
may be more intense over heavily urbanized areas than in naturally occurring
places. In the animation, red indicates the heaviest concentration of
precipitation with thick, high clouds; green are less intense storm areas,
and the thick white areas are dense surrounding clouds.
Images and Movies
Although most people probably don't realize it, GOES data is part of millions
of people's everyday lives. GOES is actually a constellation of weather
satellites used for many of the forecasts we see on television. In the
context of this research, GOES data is being used to understand a complex
weather system, rather than directly forecast coming storms.
CITY LIGHTS
OFFER CLUES ON
HOW URBAN GROWTH AFFECTS PLANTS
|
|
Europe |
North America |
Images
Growth in "mega-cities" is altering the landscape and the atmosphere in
such a way as to curtail normal photosynthesis. By using data from The Defense
Meteorological Satellite Program's Operational Linescan System, researchers
have been able to look at urban sprawl from monitoring the emission of light
from cities at night. By overlaying these "light maps" onto other data such
as soil and vegetation maps, the research shows that urbanization can have
a variable but measurable impact on photosynthetic productivity. Annual
photosynthetic productivity can be reduced by as much as 20 days in some
areas where urbanization is intense. This is not unlike turning the lights
off in a greenhouse for 20 days out of the growing season.
The findings are rich with information. In some areas with limited resources,
the research shows that human activity can increase productivity by altering
the environment. This was the case for arid and semi-arid areas where lawn
irrigation and planting changed the ecosystems from shrub vegetation and
desert to deciduous forests.
Another interesting discovery was that urbanization seems to elongate the
growing season while still reducing overall productivity. Vegetation greens
up earlier in the spring and takes longer to fade out in the fall but it
tends to have lower peak-season productivity than nearby areas unaffected
by urbanization. This could be demonstrating a profound link to the urban
heat island effect, and it has implications in climate change, particularly
in the Northern Hemisphere where urban development is most intense. As more
people urbanize highly productive land, this research should help planners
make the difficult but vital decisions necessary for responsible and sustainable
growth strategies.
CITY ZONING AND URBAN GROWTH
- A COMPARISON
Urbanization is as much a function of planning as it is of economic vitality.
From space, two large U.S. metro areas show dramatically different signals
of urban sprawl and growth, largely the result of different zoning strategies.
Portland, Oregon and the Washington, D.C. metro have both benefited from
the robust economy, with growth propelling construction and development
in both areas. But the greater Washington metro is a complex combination
of The District and municipalities in two bordering states and hasn't regulated
growth by a uniform standard. Portland on the other hand has strictly limited
urban sprawl, largely confining it to areas within city boundaries. It's
not so simple to say that one way of managing an urban area is better than
another; cities have varied personalities and needs just like people. But
many scientists hope that this research will help urban planners make better
decisions about the futures of what are coming to be known as mega-cities.
Portland, Oregon and Metro
Area
The city of Portland has strictly controlled how urbanization can spread.
As a result, the vast majority of new construction has taken place inside
the city boundaries, largely preserving the patchwork pattern found outside
the blue border you see on the screen. Across the Columbia River along the
northern border of the city, signs of wide spread growth in Washington State
appear immediately from the red points sprouting all through town. These
images were created from one set of data and shows progressive growth from
1986-1996.
|
|
Portland Beaverton |
Portland Vancouver |
Images and Movies
Washington, D.C and Metro
Area
The city limits are highlighted in purple. Surrounding it in blue is the
infamous Washington Beltway, a heavily traveled, highly interconnected loop
of road that runs around city. As the visualization flies over various locations,
notice how growth progresses over time. These images were created from three
sets of data and show progressive growth from 1973 to 1996. There appears
to be little in the way of a unified plan for construction, with red points
seeming to appear at random locations over three time intervals. It's partially
as a result of this explosive growth that population and total number of
vehicles in the D.C. area have increased roughly 13% and 22% respectively
since 1990.
Images and Movies
Shenzhen, China: Explosive
Growth Changes the Shape of the Continent
The People's Republic of China is one of the fastest growing economies in
the world. Much of the Chinese political and cultural landscape is in a
state of transition, and economic development is remarkably strong, particularly
in southern industrial cities. As seen by Landsat, Shenzhen, China practically
transforms from a regional urban center to a metropolitan powerhouse in
the space of roughly ten years. Notice how dramatically the coast changes
around the peninsula in the center of your screen. Huge structures emerge
in the waters off-shore.
|
1988 |
1996 |
Shenzhen, China
True Color
Landsat Image |
|
|
Shenzhen, China
False Color
Landsat Image |
|
|
Images and Movies
On land, note the massive signs of construction and land conversion, with
large tracts of geography being developed. By combining economic and land
use data, researches hope to better understand the relationship between
economic activity and land use change.
Spreading Urbanization
These Landsat 5 images show rapid growth around Shenzhen. Notice how
roads, bridges, and massive construction projects transform the landscape.
New structures appear off the southern coast, and highways grow less distinct
against the background as think construction projects spread along the
sides of the roads. Also notice how the massive growth alters lakes and
mountains in the area, adding sediment to the water and changing borders
of natural features.
Changes in Vegetation
As construction goes up, something has to come down. In these images,
the same scenes are presented in a way that highlights vegetation concentration.
Red indicates density of plant life, and as becomes immediately apparent,
vegetation all but disappears across the region over the last ten years.
By using data like this, researchers can better understand the causes
of environmental changes they find in cities like Shenzhen. By better
understanding the causes, researchers and policy makers hope to be able
to better monitor a region's overall health.
VIEWS OF U.S. CITIES FROM SPACE
LANDSAT AND GOES - The Satellites
Landsat
Landsat 7 Movie
Landsat 7 is the latest in a highly successful series of satellites. The
program has been monitoring the Earth for over 25 years. It roared into
orbit aboard a Boeing Delta II rocket, launched on April 15, 1999 from Vandenberg
Air Force Base in California. Managed and developed by NASA's Goddard Space
Flight Center, Landsat 7 was constructed by Lockheed Martin at their facility
in Valley Forge, Pennsylvania.
Data is available to researchers through a browsable internet interface,
and can be delivered at a relatively low cost to users.
GOES
GOES 10 Movie
The Geostationary Operational Environmental Satellite (GOES) is actually
one of a constellation of instruments positioned in fixed orbits over North
America. The GOES satellites monitor large scale weather systems, as well
as other aspects of the changing planet beneath.
For More Information on the GOES Satellite
This multimedia project is the work of a dedicated team of researchers, animators, and media specialists. A companion video to this web site is available from NASA-TV.
Below are a list of agencies, departments, and researchers who provided expertise and data for this production:
NASA - Goddard Space Flight Center
Scientific Visualization Studio
Television Production NASA-TV/GSFC
The following researchers provided source data for each attributed story:
- Atlanta Heat Island -- Dale Quattrochi, Marshall Space Flight Center
- Portland & Washington Urban Growth -- Jeffrey G. Masek, University of Maryland
- ATLAS thermal data -Burgess Howell, Global Hydrology and Climate Center
- Convection/Cloud data - Bob Bornstein & Qinglu Lin
- land use data - Chor-pang Lo, Univ. of GA
- Shenzhen Growth -- Karen C. Seto, Boston University
- Urban Sprawl and Photosynthesis -- Marc L. Imhoff, Goddard Space Flight Center
Content Preparation and Project Production-Michael Starobin/GSFC
Last Revised: July 7, 2006 at 01:07 PM EDT
|