Page Two of Three for the Earth Day 2001 Story

LANDSAT'S LEGACY

DISAPPEARING WATER: THE ARAL SEA OVER TIME

A time series is a powerful illustrative tool. Where in the case of Las Vegas we see the direct effects of people on the land, in the case of the Aral Sea, separating the countries of Kazakhstan and Uzbekistan, we see indirect, but no less dramatic effects on a different part of the world.

The Aral Sea is actually not a sea at all. It is an immense lake, a body of fresh water, although that particular description of its contents might now be more a figure of speech than practical fact.

In the last thirty years, more than sixty percent of the lake has disappeared. As you'll see in the visualization, the change over time is dramatic.

In the 1970s, farmers and state offices opened significant diversions from the rivers supplying water to the lake, sending millions of gallons to irrigate cotton fields and rice paddies. So voluminous were these irrigation sluices that concentrations of salts and minerals began to rise in the shrinking body of water. That change in chemistry has led to staggering alterations in the lake's ecology, causing precipitous drops in the Aral's fish population.

A secondary effect of this reduction in the Aral Sea's overall size is the rapid exposure of the lake bed. Powerful winds that blow across this part of Asia routinely pick up and deposit tens of thousands of tons of now exposed soil every year. This has not only contributed to significant reduction in breathable air quality for nearby residents, but also appreciably affected crop yields due to those heavily salt laden particles falling on arable land.

In the following sequence of images, we see a series of Landsat scenes taken several years apart. As the years pass, we see the profound reduction in overall area covered by the Aral, and a commensurate increase in land area as the floor of the sea now lies exposed.
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LAKE CHAD DISAPPEARING

Planetary change is neither simple nor easily explained by an individual cause. Where the Aral Sea's demise is largely the product of years of direct mismanagement and human hubris, reasons for change in another vast body of fresh water are less easily identified. But as we'll see in this sequence, the ability to monitor that change over time offers researchers insights that might otherwise not have been possible from ground based observations.

When it thrived, Lake Chad was one of those ironic points of planetary formation in that it seemed to defy the vast ocean of sand directly to its north. Located on the edge of the Sahara and bordering four countries--Chad, Cameroon, Nigeria, and Niger-- the immense area of this land locked lake has nearly disappeared in recent years. Persistent drought has caused the lake to drop from its former sixth place position in the list of world's largest lakes; it is now one tenth it's former size.

The basin of the lake is not naturally deep, so the surface area of the lake tended to spread out, keeping the total depth to little more 23 feet (7 meters). In recent years, rainfall patterns have begun to change, and tributaries to Lake Chad have not been refilling the basin as rapidly as they used to. The lush, productive flora and fauna fed by the wetlands of the shallow lake have suffered as a result. This has led to significant changes for various communities of people that live in the vicinity of the Lake. While for some the now exposed lake bed has enabled new land to be cultivated, much of the available fresh water that might have been used for irrigation is no longer dependable. As rainfall rates appear to be declining year after year, people living nearby develop even greater dependence on the lake, draining it even faster.

The Landsat images showing the dramatic decrease in Lake Chad's size can not only help quantify the changes there, but can help researchers evaluate the root causes for such large transformation events on Earth, from climate change to human use of natural resources.
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MOZAMBIQUE FLOODING

Following weeks of heavy rains in late Winter 2000, massive flooding inundated wide tracts of eastern and southern Africa, displacing more than 200,000 people. Torrential rains fell over wide areas. Vastly overflowing rivers sent much of that water rushing towards Mozambique, which has been one of the hardest hit countries. The catastrophe provoked international efforts to aid victims from the rushing waters, but extreme devastation nonetheless befell dozens of towns and villages. In addition to heavy rains, Cyclone Leon-Eline pounded the region on February 23rd, blanketing a wide area already saturated with sheets of rain.

This side by side Landsat sequence shows the comparative size of rivers in Mozambique before and during the floods. Notice how the high waters have all but covered the lowlands, far exceeding the boundaries of the normal river system.
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MOZAMBIQUE FLOODING COMPARED TO SIZE OF WASHINGTON DC

This sequence shows the scale of the tragic floods that washed through Mozambique in 2000. As the visualization begins, we see the relative size of Washington, DC, shown in red, superimposed over the flood area. In this case, remote Earth imagery becomes useful as a tool for communication, allowing accurate and clear description of the scale of a particular natural event.
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MT. ST. HELENS OVER TIME

September 1973 May 1983 September 2000
The explosion of Mt. St. Helens volcano in Washington State on May 18, 1980 sets the scene for one of Landsat's most important capabilities. As a means for archiving surface features, researchers can study how the Earth changes over time. In this sequence, pictures of the mountain taken in 1973, 1983, and 2000 show how the eruption changed the surrounding area. Notice how the north face of the mountain dramatically changed following the blast. The crater's mouth elongated, and significant ash deposits altered the down slope terrain.
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THE BIG BREAK--ANTARCTIC GLACIER CRACKS



When NASA glaciologist Bob Bindschadler saw the picture, he knew he had found something important.

Taken by the Landsat 7 spacecraft, the image in question showed a thin, 25 kilometer (15 mile) crack in what's called the Pine Island Glacier in Antarctica. What surprised him and the scientists he immediately contacted was the fact that images taken just ten months before showed no sign of such a fissure. A major break was forming in the Antarctic ice, and he and his colleagues had caught it in the act.

Further study would show that the tear in Antarctica's icy cloak had happened in a period of little more than five weeks. Although the speed of the crack seems to have slowed as it picks its way across the ice, Bindschadler says he believes there will be a huge new iceberg falling into the south seas within the next year and a half or so, assuming the crack continues to grow.

The Landsat 7 spacecraft actually passes over the southernmost continent 16 times a day as it orbits the Earth. During the southern summer months, the instrument takes an average of 300 images per week. This regular acquisition of surface information is what enabled researchers like Bindschadler to keep track of relatively sudden changes to the surface of the Earth.

In fact, by employing a clever strategy of image acquisition and processing, researchers hope to reveal important details about Antarctica following this year's data collection. Previously the spacecraft took images of the surface as it flew towards the pole. But this year marked a change. For the first time, images were taken as the spacecraft moved past the pole--heading away, in other words. What this does in practical terms is offer a different angle on already catalogued features. The change in viewing angle helped expose detail that could not be seen from the other direction.

But there's more. By combining the two angles, experts will not only be able to see things in the ice they've never seen before, but will also be able to infer detail about the land and ice hidden below the surface. This is because surface features on wide stretches of ice tend to reflect the contour, shape, and texture of more durable material underneath. By getting a refined picture of the ice on top, new pictures of the hidden ground underneath suddenly become possible like never before.
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SHENZHEN, CHINA 1988-1996:EXPLOSIVE URBAN GROWTH CHANGES THE SHAPE OF A CONTINENT

True Color Sequence
Shenzhen, China 1988 Shenzhen, China 1996

The People's Republic of China is one of the fastest growing economies in the world. Additionally, 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, Shenzen, China practically transforms from a regional urban center to a metropolitan powerhouse in the space of roughly ten years. Notice along the southern peninsula as the actual outline of the land changes, with huge structures emerging in the waters off-shore.

Landsat 5 collected the data. You can see 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 significant building spreads along the sides of the roads. Also notice how the massive growth alters lakes and mountains in the area, adding sediment and changing borders.

Changes in Vegetation--False Color Sequence
Shenzhen, China 1988 Shenzhen, China 1996

As construction goes up, something has to go 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, and better monitor a region's overall health.

LOSING FORESTS IN BOLIVIA



This scene starts in space, high above South America. As we zoom in closer, we see the national outlines of Bolivia come into view on the map.

By focusing on one particular region, we're able to see effects of deforestation in the equatorial forest. The sequence that follows shows two images of the Santa Cruz region of Bolivia. The first was taken in 1984. Landsat 7 took the second in 2000. In just a few short years, we see how intense agricultural development has transformed the forest.
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COLORADO MOSAIC



Using the data collected by the versatile Extented Thematic Mapper Plus instrument onboard the Landsat 7 satellite, we can take a tour of Colorado in a way that was impossible just a few years ago.

This virtual fly-over of Colorado is the product of dozens of Landsat scenes digitally stitched together into a single, unified mosaic. We see the state as an unbroken whole, but only after it's been cut into manageable sections, beamed to Earth, stored, retrieved from the Landsat database, assembled, and digitally reprocessed.
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TREES FALLING:MAPPING DEFORESTATION IN RONDONIA, BRAZIL



Throughout much of the 1980s, deforestation in Brazil eliminated more than 15,000 square kilometers (9000 square miles) per year. That pace has only increased through the 90s and into the 21st century.

Brazil is also home to more than a quarter of Earth's tropical forests. Considering that the band of lush green that circles the globe through many equatorial nations is fundamental to the overall health of the whole planet's environment, careful monitoring of forest health in the tropics is essential. Tropical forests act as major carbon "sinks", places where ambient carbon dioxide in the atmosphere can be absorbed by growing things and sequestered for years. Definitive evidence shows that excess carbon dioxide can contribute to the greenhouse effect and speed global warming. Similarly, tropical forests also act as a primary producer of oxygen. In the respiration process that absorbs gaseous carbon dioxide, trees and other plants give off oxygen. It is for these and a host of other reasons why scientists and policy makers need to monitor and forestall wholesale deforestation.

This sequence shows how profligate clear cutting can influence that trust. Data gathered over time by several in the Landsat series of spacecraft shows enormous tracts of forest disappearing in Rondonia, Brazil. This territory underwent an enormous rise in population towards the end of the twentieth century, buoyed by cheap land offered by the national government for agricultural use. As you see the visualization progress, it's useful to note how the human phenomenon of deforestation generally works, especially in the dense tropical forests of Brazil. Systematic cutting of a road opens new territory to potential deforestation by penetrating into new areas. Clearing of vegetation along the sides of those roads tends to fan out to create a pattern akin to a fish skeleton. As new paths appear in the woods, new areas become vulnerable. The spaces between the "skeletal bones" fall to defoliation, and another inch of the Earth's biological rudder is no longer reliably steering the planet into the future.
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Click Here for Page Three

 Special Thanks to Dr. Jon Ranson, Terra Project Scientist and Darrel Williams, Landsat Project Scientist.

Portions of this multimedia presentation includes material from Space Imaging L.P.

For further information about Landsat, Terra, EO-1, remote sensing, Earth science conducted by NASA and its partners, or related topics, check out the following web sites:

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:

NOTE: All SeaWiFs images and data presented on this website are for research and educational use only. All commercial use of SeaWiFs data must be coordinated with ORBIMAGE.


Please give credit for these images to:
NASA - Goddard Space Flight Center
Scientific Visualization Studio
Television Production NASA-TV/GSFC
The SeaWiFs Project and ORBIMAGE

Content Preparation and Project Production: Michael Starobin

Last Revised: February 4, 2019 at 06:02 PM EST