While picks, shovels, mesh screens and fine brushes for cleaning tiny shards of pottery are still classic tools of the archaeology trade, so are high tech tools like global positioning systems, remote sensing instruments and satellites. Archaeology is the study of history and past cultures through the things left behind -- from buildings and monuments, to pottery, to bits of discarded food. This science depends on tangible objects that can be seen or touched. Finding those things that tell us about our past is the trick, the first critical step, in reconstructing the past.
One of the newest and most promising ways to search for clues is with remote sensing, which uses sophisticated imaging instruments on aircraft, the space shuttle and satellites. In addition to giving archaeologists a regional perspective that is impossible to get in any other way, remote sensing instruments also have the ability to detect and measure things that would otherwise be invisible. "Remote sensing extends humans' perceptual abilities -- it lets you see things your limited human senses can't see," says Ron Blom, JPL geologist and one of the discoverers of the lost city of Ubar. In ancient times, Ubar was the jumping off point in the southern Arabian Peninsula for frankincense-laden camels on a trans-desert journey to ancient Rome, Greece and Mesopotamia.
A key to finding this old fortress was visible and reflected infrared images from the Landsat satellite and radar images taken from the space shuttle. These images revealed a regional network of tracks, some used by camels more than two thousand years ago and by 4-wheel-drive vehicles today, that pinpointed the city's location. "The resolution is such that you don't see structures -- but you can see things like pathways from one caravansary, or water hole, to the next," said Blom.
Radar images from another space shuttle mission also helped researchers find a previously unknown section of the ancient city of Angkor in Cambodia. A huge complex, now largely hidden beneath dense jungle growth, Angkor once housed more than a million people. Imaging radar, flown on airplanes, satellites or the space shuttle, can see through tree canopies, vegetation, clouds and the dark of night. It can even look several feet below Earth's surface when the conditions are right. "We've verified with a shovel that it can see through at least 6 feet of dry sand in the Sahara," explains Blom.
In Cambodia, radar picked out irrigation canals north of the main temple area, showing that the city had extended further than had been known before. The radar data became an important tool for the World Monuments Fund and researchers in their study of the how the city grew, flourished and died over an 800-year-period before becoming one of the world's great archaeological ruins.
In Chaco Canyon, New Mexico, researchers found prehistoric roads using a remote sensing instrument capable of detecting small changes in heat on Earth's surface. The instrument, the airborne precursor of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) now flying on the Terra satellite, detected more than 200 miles of a prehistoric roadway system, as well as ancient buildings and fields.
"Remote sensing is especially good for revealing what the environment is like and what it may have been like in the past," says Blom. "Our ancestors were more dependent on their local environments than we are for food, water and basic necessities. They traded to get the other things they needed. In the future, remote sensing may allow you to know what would have been favorable environmental locations and conditions for human activities and predict good places to look, in other words, a target finder. Collaboration between archaeologists and technologists is critical to exploiting this potential."
"Our collective cultural heritage is being stolen, destroyed by development, or paved over at a faster rate than it is being discovered and documented. Space technology," says Blom, "is one tool to help make discoveries and document them."