SAN FRANCISCO — Ten years after its launch and nine years beyond its expected lifespan, NASA’s Earth Observing-1 (EO-1) satellite and Hyperion imaging spectrometer are providing archaeologists with an additional tool for identifying previously undiscovered sites that merit excavation.
Hyperion imagery is being used by Tom Levy of the University of California, San Diego, to find ancient copper smelting areas in Jordan and by Bill Middleton of the Rochester Institute of Technology in New York to create detailed maps of the area inhabited by the ancient Zapotec civilization in Mexico.
Hyperion was not designed for this type of work, but the sensor built by Northrop Grumman Aerospace Systems of Redondo Beach, Calif., which offers detailed resolution of hundreds of spectral bands, has proved useful for archaeology because it can detect subtle surface features that give archaeologists clues to the history of an area, said Betsy Middleton, EO-1 mission scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. Hyperion also is the only imaging spectrometer in space that is available for civilian use, she added.
When it was launched in November 2000 as part of NASA’s New Millennium Program, the EO-1 satellite, built by Beltsville, Md.-based ATK Aerospace Systems Group, was designed to demonstrate advanced imaging instruments as well as new techniques for obtaining detailed Earth imagery that could be sold to government and commercial customers. Ten years later, the satellite has succeeded in demonstrating new technology while also validating software for autonomous operations and acquiring more than 100,000 images with Hyperion and the Advanced Land Imager, an instrument developed by the Massachusetts Institute of Technology’s Lincoln Laboratory in Lexington to obtain spectral data in nine wavelengths and offer detailed panchromatic imagery.
In spite of its important contribution, EO-1 is just one of the many satellites providing archaeologists with clues to the location of the buried remains of ancient civilizations. For example, Payson Sheets of the University of Colorado in Boulder is using color infrared imagery to trace ancient footpaths in Costa Rica. Satellite imagery offers the telltale signs of buried footpaths because the plants growing over those tracks appear healthier and their roots thicker than those of the vegetation on either side, Sheets said.
Similarly, Sarah Parcak of the University of Alabama, Birmingham uses infrared imagery to find slightly elevated areas of the Nile River Valley where her team uncovers mounds filled with layers of artifacts from ancient settlements. Parcak also has been able to detect the chemical composition of those mounds filled with mud-bricks and pottery due to their unique spectral resolution. In her work, Parcak has used satellite imagery captured by NASA’s Advanced Spaceborne Thermal Emission and Reflection Radiometer, the U.S. government’s Landsat satellites and Longmont, Colo.-based DigitalGlobe’s WorldView-1, WorldView-2 and Quickbird satellites.
“When I started this work 10 years ago, no method had been developed to use satellite imagery to detect archaeological sites in Egypt,” Parcak said. Now, remote sensing tools are helping scientists find entire settlements and buried architecture, she added.
The use of satellite imagery, once considered experimental, has entered the mainstream as archaeologists around the world rely on a variety of instruments to find ancient civilizations. “We have had such success with satellite imagery and people realized there are some things we can detect with remote sensing could not be perceived from the ground,” Sheets said. In addition, archaeologists attribute the increasing popularity of remote sensing to the growing availability of high-resolution imagery and the easy access to that imagery provided by the Internet.
While satellite imagery is a useful tool, no archaeological study can be completed without visiting the site. “You can say what you want based on imagery, but you can’t prove anything without ground verification and excavation,” Parcak said.
Improvements in satellite imagery, however, are making those site visits much quicker and more effective. To quantify that time savings, Parcak compared a recent survey she conducted after extensively mapping an area using satellite imagery with the amount of time that survey would have taken using conventional ground-based surveying methods. She determined that without the benefit of satellite imagery her two-week survey of 70 previously unknown Egyptian settlements would have taken more than three years.
Continued advances in satellite technology spur the use of remote sensing in archaeology. “It seems like every other year new satellite imagery is released with better spatial and spectral resolution,” Parcak said.
While governments and commercial satellite builders continue to improve upon remote sensing technology, the aging EO-1 is not expected to be replaced by a U.S. follow-on anytime soon. The 10-year-old satellite remains in good health with enough fuel to last at least one more year, said Dan Mandl, EO-1 mission manager. When the fuel is gone, the satellite could still capture imagery as its orbit slowly lowers, he added.
No Earth Observing-2 satellite is included in NASA budget plans. Similar capability will be offered by Germany’s Environmental Mapping and Analysis Program, a hyperspectral satellite mission scheduled for launch in 2014, NASA’s Middleton said.