FROM a flint hand axe dating back to the early Ice Age to Oman's lost city of frankincense (see story Page 13), archaeologists are finding ancient artifacts by studying pictures of the earth taken from space. Using remote-sensing techniques to aid their research, scientists have uncovered treasures hidden underground for thousands of years.
"Remote-sensing is just seeing from afar," says James Wiseman, chairman of the Boston University (BU) Department of Archaeology, who employed this technology in a project near Preveza, Greece.
"It is an instrument that we use to discover things without having to see or touch them," says Farouk El-Baz, director of the Center for Remote Sensing at BU. The technique is useful in archaeology, he says, because it provides detail over a large area and at great depth. A remote sensor on a satellite can take images from 570 miles above the earth. Because the sensor is actually a multispectral camera that uses the electromagnetic spectrum (energy waves) to detect objects, artifacts buried as deep as 30
feet below the surface can be found. The electromagnetic spectrum includes energy waves from infrared, visible or ultraviolet light, X-rays, and radio waves.
"Images taken through remote-sensing show evidence of previous human habitats by depicting patterns of civilization such as the remains of cemeteries, abandoned roads, or dry river beds" that are presently covered with sand, soil, or water, says Dr. El-Baz. "The electric current given off picks up anything that is different from the existing soils."
Smaller scale remote-sensing instruments suspended from aircraft, blimps, or even a scientist's hand can be used to zoom in on details.
Dr. Wiseman's project makes use of all the types of remote-sensing instruments. The project covers 400 square kilometers (154 miles) of terrain, from the Ambracian Gulf to the Adriatic coast and a time period of several thousand years.
"We're looking at piecing together the cultural history of the ancient city of Nikopolis in Epirus, Greece, and explaining the changing relationships, from prehistoric through medieval times, between the people that lived there and the land they inhabited," Wiseman says.
"Using remote-sensing," he continues, "We can research a project the size of ours and have results within three to five years. Before, it would take three generations of archaeologists to walk the area, make observations, dig a little here or there, and hope that they found something.
Last summer, a member of Wiseman's group, Curtis Runnels, uncovered an Acheulean hand axe. This axe, named after the French city of St. Acheul where the first one was found, is evidence that ancestors of modern humans inhabited the Greek peninsula during the Lower Palaeolithic period of the early Ice Age, some 200,000 to 500,000 years ago. This is the earliest indication of human presence in this country.
By examining satellite images taken with remote-sensing technology, Wiseman matched the landscape where the axe was found with similar areas on the photos to identify digging sites. Within the first summer of research, Wiseman's group uncovered a number of tools of the same time period as the axe.
Wiseman became fascinated with this area of ancient Greece in 1959, while attending the American School of Classical Studies in Athens. The school is sponsoring the Nikopolis project, a joint undertaking with the Greek Archaeological Service.
Nikopolis was built by Octavian Caesar after he defeated Mark Anthony and Cleopatra in the Battle of Actium in 31 BC. Caesar crowned himself Rome's first emperor, and Nikopolis was known as "Victory City." Two types of remote-sensing are used. The first, a radar sensor, such as the one used on the National Aeronautics and Space Administration's space shuttle, transmits radar waves. When these waves hit an object on earth, such as a rock, they bounce back to a receiver. This returned transmission is assig ned a value by the instrument.
The second sensor is used on the United States Landsat satellite. It detects invisible infrared light and visible light (sunlight reflected by the object) and records color bands in digital form.
Values produced by both sensors are fed into a computer, which generates a color map of the area, like that shown on the computer screen in the photograph on Page 12. For example, an ancient quarry in one area will appear red on the computer screen. All other quarries, no matter how far away, will also appear red. Each color is that object's "spectral signature."
With a photograph of the image in hand, archaeologists go to the area pictured and survey the landscape to determine what color matches what surface feature. This process is called "ground-truthing." The image can help them identify likely excavation sites.
Besides archaeology, remote-sensing can be used as an aid in many types of projects.
The Kuwait Institute for Scientific Research has asked the BU Center for Remote Sensing to evaluate how the Gulf war damaged Kuwait's desert and coastal area.
"We are comparing satellite images before the war and after the hostilities ceased," El-Baz says. "Through computer manipulation we can see what exactly changed and how.... We have seen for example, that the area disturbed in the desert by military activities resulted in the formation of large sand dunes that are now encroaching up the roads."