Aerial archaeology basically finds locations that may be suitable for further investigation by getting higher than ground-level. Balloons and kites were the first means used in the 19th century, although any method that attains a better than ground-level view might work.
Leonard Wooley located tombs in Egypt after climbing a hill and looking below. Earl Morris, one of the pioneer archaeologists in the southwestern United States, climbed telephone poles to snap aerial photos with his camera.
Finding Sites on Two Feet
Archaeologists often locate sites by searching through documents and local stories. They also walk through prospective sites, looking for prominent features such as remnants of walled buildings or burial mounds. Sometimes this kind of survey provides enough evidence for a full archaeological dig to take place.
But many sites may be spotted this way only by finding artifacts scattered around, and this method, while fortunate in its discovery, may not yield an accurate picture of the size and breadth of the location. So merely digging in one spot may miss a wealth of other archaeological material that may be just a few years away.
Purpose for aerial survey
Archaeologists may walk and explore a possible site, find a ruin, set up camp, and start to dig, reveling in their discoveries. However, they may miss the next site that could lie over the hill, or even at the top of the hill, because the hill was not climbable and no path up or around it existed. Aerial photography can spot such a site, like the Cerro Gallo Trinchera hilltop.
Also, establishing a dig at all in a specific site may not always be possible. Time needed to make the dig may not be available, or funds non-existent. The site may require permission to dig, which is not forthcoming. The terrain may not be hospitable to allow serious digging to take place. Survey by aerial means is non-invasive, and requires only cameras, radar, maps, compasses, and perhaps a laptop.
Short History of Aerial Archaeology and Photography
Photographs of the ancient Roman harbor town of Ostia were taken from a balloon in the early 20th century, ushering in the first archaeological applications of aerial photography. In Sir Henry Wellcome, philanthropist and pharmacist, took vertical pictures of his excavations in the Sudan by using a box kite.
In 1925 Syria Father Antoine Poidebard began tracing ancient caravan routes using air observation and discovered many new forts and roads. The ancient harbor beneath the sea at Tyre in Lebanon was discovered using aerial photography.
21st Century Aerial Photography and Archaeology
Today, aerial survey is one of the most important tools for the discovery of archaeological sites. Each year, hundreds of previously unknown sites, ranging in date from the Neolithic (late Stone Age, from circa 4000 BC) to present time, are discovered.
Everything from Neolithic long barrows to the farms and fields of the Bronze and Iron Ages, Roman villas, medieval villages, and a wealth of detail about the defense of the British Isles during World War II. Polish and Viennese archaeological organizations are using aerial photography and survey to map sites in their countries.
A major aerial reconnaissance project undertaken in the 1970s by the National Park Service in Chaco Canyon in the American Southwest, disclosed an ancient road system extending about 1500 miles through the Canyon. Aerial photography and archaeological interpretation is used in England to show that there are buried sites, visible only from the air, that the landscape around Stonehenge was intensively occupied from Neolithic times to the present day.
High altitude mapping has also helped reveal a previously undocumented people in Costa Rica. In 1984-5, the area around the Arenal volcano was scanned with radar, infrared photographic film and other remote sensing techniques. This area had been of interest since local people had found potsherds and tools.
Resulting images showed roadways radiating out from a central graveyard. Subsequent excavation of 62 sites showed that from about 11000 BCE, people had lived in the volcano's shadow and had settled permanently on the shore of Lake Arenal in 2000 BCE. Then their entire settlement had been buried by a volcanic eruption.
In western Illinois at a site called New Philadelphia, archaeologists continue work at this site, the first American town founded by a free African-American, decades before the Civil War. The archaeologists use aerial photography and survey to map out sites in the area.
Aerial photographs are not always sufficient to reveal potential archaeological sites. They must be interpreted by the archaeologists, who examine the terrain using topographical maps along with the photographs in order to distinguish traces which could be archaeological in origin from other natural features such as river beds, or man-made features such as vehicle tracks.
Google Earth and other high-resolution satellite images and thousands of aerial photographs all over the world already have recorded most of the planet. These can be examined for archaeological evidence.
Google Earth can even be used to examine the ground and look for archaeological sites, although most users are not trained to interpret photos and images. Aircraft can search the ground for traces of former sites and past landscapes.
Features photographed from the air are generally labeled as Earthworks, Soil-marks, and Crop-marks. These descriptions refer only to the way the features are revealed. Earthworks describe either banks of waterways and associated ditches, or stone-walled ruins, i.e. any feature seen in relief which are dependent on lighting and weather conditions.
Soil-marks are changes in the color of subsoil when the ground is ploughed and turned over, then revealing the presence of buried ditches or foundations. Crop-marks develop when a buried wall or ditch decreases or enhances crop growth by affecting moisture and nutrients in the soil. Crop-marks are difficult to interpret because they can be easily seen in one year but invisible the next year.
Future of Aerial Archaeology
Two hundred years ago, neither cameras nor airplanes existed. Today these tools are part of commonplace technology in many fields. Who knows what a Flinders Petrie or an Earl Morris might have discovered had they had cameras and helicopters. Who knows what might lie in still uncharted areas of our world.
Would you want to find out?
Renfrew, C. & Bahn, P. (2008). Archaeology Today, 5th edition. Thames & Hudson.