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Looking Into the Past From Space

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One hot, unusually dry summer in my early teen years, the reservoir near my Idaho home all but disappeared.  As the water receded, the remnants of a town emerged. The town had been relocated when the reservoir was built in the 1920s, but much had remained under water. Decades later, walking through the crumbling foundations and uncovering mud-encrusted artifacts, it was easy to imagine life in that other era.

Fast-forward a couple of decades, and I find myself looking into the past again, but this time I have information beyond hints and imagination. I have more than 40 years worth of satellite imagery showing change across Earth’s landscapes.

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In 1972, NASA and the U.S. Geological Survey launched the first Landsat satellite into orbit around the Earth, and since that time, at least one Landsat satellite has always been in operation. The record is set to grow into the future with the launch of the Landsat Data Continuity Mission (Landsat 8) on February 11, 2013. We will be able to compare the view offered by Landsat 8 with observations taken by the first Landsat and every subsequent Landsat, providing the longest continuous space-based view of land in existence. With Landsat, I can literally see into the past.

The sweeping look across four decades is becoming more and more important as we face changes from both land use decisions and climate change. By understanding how our decisions in the past have affected the land, we can make more informed decisions in the future.

For example, Dr. Alan Belward of the European Commission’s Joint Research Center uses Landsat data to map the world’s forests to give policy makers the information they need to make tough choices about how to use limited resources. “It’s only by viewing Landsat data that we would know how quickly the world’s forests are being destroyed,” says Belward. “We’re losing about a football field worth of forest every four seconds of every minute of every day.”

Not only does this mean that we have fewer trees removing carbon from the atmosphere, but also that much of the carbon formerly stored in those trees ends up in the atmosphere. In fact, deforestation and other land use accounts for 10 percent of all carbon emissions related to human activity. Rising concentrations of atmospheric carbon dioxide is the primary cause of climate change.

Deforestation in the Amazon Rainforest

Deforestation in the Amazon Rainforest takes on many different patterns. In Rondônia, a state in Western Brazil, deforestation took on the fishbone pattern revealed in these Landsat images from 1975 and 2012. NASA image courtesy of Landsat team. Caption by Aries Keck.

Climate change is just one reason to keep the world’s forests intact, but limiting deforestation isn’t easy. Forests are cut down to clear land to grow food or raise livestock to support a growing population. When Landsat 1 launched in 1972, the world’s population was just under 4 billion. Today’s population exceeds 7 billion, and Landsat has seen that growth. Cities across the world have expanded, and agriculture has been transformed as we have found new ways to produce food.

“The basic fact is that natural resources, like forests and land to grow crops, are getting more and more scarce,” says Belward. “To make sensible decisions on trade-offs between different uses, you need evidence on where these resources are, what sort of condition they’re in, and how they’re changing.”

Landsat is ideal for decision makers because each pixel or image element in a Landsat scene is 30 meters, about the size of a baseball diamond—the scale at which land-use decisions are made.

What would you see if you looked back across 40 years in your hometown? Thanks to a USGS decision to provide Landsat data free of charge, the entire Landsat archive is available to you and your students. Browse the archive using the LandsatLook Viewer , then download these tutorials to learn how to get the data and make images. This standards-based classroom activity will help middle and high school students identify and measure landscape changes captured in Landsat images.

Maybe the changes you see today will inspire decisions that will be visible to the next Landsat, which NASA launched from southern California on February 11, 2013. The Landsat Data Continuity Mission—the eighth satellite in the Landsat series—will be the best Landsat satellite to date. It will be more sensitive and more reliable than earlier Landsat satellites. More importantly, it will continue the Landsat record into the future, and that matters because, in the words of William Shakespeare, what is past is prologue.

To learn more about Landsat and other NASA satellites, watch NOVA’s “ Earth From Space .”