Dec 3, 2000

EO-1: It's not just a good idea, it's the law!

NASA's Earth Observing-1 satellite blasted off last week with a payload of new instruments that could revolutionize remote sensing.

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December 4, 2000 -- At first glance, last week's launch of a Delta II rocket carrying the Earth Observing-1 (EO-1) satellite into orbit seemed routine. After all, NASA has plenty of Earth-watching satellites. What's so special about this one?

For one thing, it was required by law.

"I've been at NASA a long time; EO-1 is the only project I've ever worked on that was required by a federal law," said Dr. Bryant Cramer, who has worked at NASA since 1978.

What could be so important that Congress would go to the trouble of passing a special law, when NASA's projects are normally specified in appropriations bills? 

The law -- called the Land Remote Sensing Act of 1992 -- directed NASA to ensure that a national archive of Landsat satellite images that documents the Earth's surface since 1972 would be maintained into the future without interruption. The archive, as expressed in the law, is "particularly important for national security purposes and global environmental change research."

Right: A Delta II rocket carrying the Earth Observing 1 satellite blasted off from Vandenberg Air Force Base, Cal., last Tuesday at 10:24 a.m. PST. For a 192 kb Quicktime movie of the launch, click here.

"It is the only continuous record of the Earth's land surface from space that we have -- that the world has," said David Steitz, public affairs officer for NASA Headquarters in Washington, D.C.

NASA designed EO-1 to flight test next-generation remote-sensing technologies that are smaller, lighter, cheaper and better than their predecessors. If the tests are successful, these technologies promise to enable the business of remote sensing (i.e., using satellites to capture data and images of the Earth's surface).

Ultimately, NASA hopes that the cost savings and shorter mission development times allowed by these new technologies will encourage private industry to venture into the remote sensing business. NASA could then perpetuate the national archive by purchasing the images from the private companies, rather than building and operating the satellites itself -- a goal explicitly stated in the law.

The Landsat legacy

This visual "diary" of the Earth's surface is kept by the U.S. Geological Survey at the Earth Resources Observation Systems (EROS) Data Center in Sioux Falls, South Dakota.

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The EROS Data Center serves as a treasure chest of information for researchers and local governments interested in a wide variety of natural and urban issues.

"The archive data is good for looking at urban growth or urban planning; it certainly looks at productivity of crops; it looks at forest management; it looks at natural disasters, for example floods or volcanoes; it looks at some cases of pollution, like people dumping things into coastal waters," said Cramer, program manager for the New Millennium Program (NMP) at NASA's Goddard Space Flight Center. The NMP produced EO-1 as part of its mission to promote next-generation space technologies.

Left: An example of an image from a Landsat satellite. In this false-color image, vegetation appears red, water appears black or dark blue, and urban areas appear light blue or blue-green. IJsselmeer, Netherlands, 1973.

The archive is not classified, and all of its data and images are available to the public -- for a fee. Currently, the fee is $600 per frame, but one of the goals of the law is to bring this cost down through commercialization of the remote-sensing industry.

Images from a variety of sources are stored in the archive, including the 30-meter resolution images taken by the Landsat series of satellites. The federal law applies specifically to the continuation of the Landsat legacy.

The first of the Landsat satellites was launched in July 1972, and it didn't take long for Landsat 1 to prove its usefulness.

In 1972, the Soviet Union experienced a major wheat crop failure. The U.S. had sold large quantities of wheat to the Soviet Union at low prices before the crop failure was announced. The failure drove up wheat prices, and the U.S. ended up buying wheat back from the Soviets at a loss. 

"When we started selling it, we were selling it for $1.92 a bushel, and we ended up buying some of it back at $4 or so a bushel," said Dr. Forrest Hall, senior research scientist at NASA's Goddard Space Flight Center.


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"That really made us realize that our conventional (crop-estimation) systems at that point were not very accurate," Hall said.

In order to add an element of stability to the world's agricultural markets, NASA and the U.S. Department of Agriculture began a program to see if Landsat data could be used to estimate global crop production.

The Landsat satellites break up incoming light into several "bands," each spanning a certain range of frequencies (the frequency of light is what determines its color). Analyzing these bands allowed the scientists to map the acreage and maturity of the wheat crop.

"You're basically looking at the unique way in which vegetation reflects light," Hall said. "Vegetation reflects light differently than soil or concrete or rooftops or trees. Each crop has a unique pattern of reflectance, and that pattern changes as the crop develops over time."

By 1976, Landsat 1 and Landsat 2 were making estimates of crop production for wheat and other grains around the globe. These estimates turned out to be accurate within 10 percent, which was the goal of the project, Hall said.

"It was a successful experiment, and that was the first use of Landsat data on a global scale," Hall said.

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Since the mid-1980s, scientists have increasingly used Landsat data to monitor and document global change, such as urban sprawl and deforestation.

"People are now looking at the almost 30-year record of Landsat data and comparing multiple images to monitor the rate of change of the landscape," Hall said.

In one recent environmental application, scientists used Landsat data to document the decline of nearly 900 coral reefs around the world. By quantifying the destruction of the reefs, scientists hope the Landsat data can add weight to arguments for taking political steps to protect the remaining reefs.

Left: An image of the Florida Keys taken by Landsat 7. Scientists will use similar images to document the decline of the world's coral reefs, which is thought to be due to rising water temperatures as a result of global warming.

Making the transition to the new millennium

"The whole purpose of ensuring Landsat data continuity is that there are many global processes that change slowly," Cramer said.

"So if you're going to detect, understand, and potentially manage these changes, you've got to have long-term data that -- even though it's collected over several years by many different instruments on different satellites -- they all have to be comparable, so that when I'm trying to track a change that occurred over 30 or 40 years, I've got a data set that will support that kind of analysis," he said.

Last week's launch of EO-1 represents a bridge spanning the transition from old technology to new.

The land-imaging instruments on EO-1 have the advantage of being much smaller and cheaper than those used on previous Landsat missions.

But because the new instruments are based on entirely different technologies than the old ones -- largely adapted from the burgeoning computer industry -- NASA scientists and engineers must check to see that the new instruments can produce images comparable to those produced by the old instruments. Otherwise, side-by-side comparisons of future and past data will be useless.

To achieve this, EO-1 will be placed in an orbit just behind the current Landsat satellite, Landsat 7. This "formation flying" will allow EO-1 to take a picture of the same scene as Landsat 7, only one minute later.

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Right: This rendering of EO-1 (top) and Landsat 7 (bottom) over South America gives an impression of the relative size the two satellites. Click on the image to see a 95 kb Quicktime movie illustrating formation flying.

Comparing the images, scientists can tell how well EO-1 mimics the instruments on Landsat 7.

By developing and flight testing these advanced land-imaging technologies, NASA hopes to jump-start the commercial remote-sensing industry. Privatization of remote sensing is a long-term goal of the federal law.

To that end, NASA will hold a workshop in January for companies interested in incorporating these technologies into future remote sensing endeavors.

"What we're trying to do is to flight validate these technologies and thereby lower their risk," concluded Cramer, "making them available to future science missions sooner than they would be otherwise."

Web Links

Earth Observing-1 home page -- Provides a wide variety of information about the EO-1 satellite, including images and related links

EROS Data Center -- Home page for the USGS archive containing the Landsat data. Images of the Earth's surface since 1972 can be ordered from this site

Landsat 7 Home Page -- Sample images and information about the Landsat series of satellites

New Millennium Program -- Home page of the NASA program that built EO-1. Includes information on Earth Observing-3 and other advanced-technology satellites

Landsat Data Continuity Mission -- Details about the initiative to maintain the continuity of the Landsat archive

Delta II launch -- 192 kb Quicktime movie of the launch of EO-1

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