The Desert Leaf June 2014 : Page 32
Archaeologists Take to the Skies by Claire Rogers Henry D. Wallace, courtesy Archaeology Southwest Excavated prehistoric Hohokam pit-house foundations, many ringed by postholes marking their former walls, were visible at a site north of Gila Bend in January 2008. The houses uncovered by Desert Archaeology, Inc., during this excavation were extraordinarily large by prehistoric standards. The image was taken from small, sport plane (often called an ultralight). 32 DesertLeaf l June 2014
Archaeologists Take To The Skies
Excavated prehistoric Hohokam pit-house foundations, many ringed by postholes marking their former walls, were visible at a site north of Gila Bend in January 2008. The houses uncovered by Desert Archaeology, Inc., during this excavation were extraordinarily large by prehistoric standards. The image was taken from small, sport plane (often called an ultralight).
Archaeologists are often pictured hunched over tiny potsherds buried deep in layers of soil. However, in recent years, they can be found looking to the sky for the last sighting of their camera-toting balloon, kite or unmanned aerial vehicle.
Or, they might be seen poring over colorful, highresolution radar images or using data fi lters to digitize features picked from satellite images. In these ways, archaeological researchers are collecting valuable details about enigmatic ancient societies.
Minuscule, broken, discarded artifacts have been the domain of many archaeologists, but so too has been the big picture. Entire landscapes can offer cryptic indicators of those who came before, and prehistorians have known that very subtle disturbances on the surface may be the tip of hidden clues.
But discerning these irregularities often requires a view from above, a view from a specific angle, a view from many sets of eyes, or even a view from computer enhancements.
According to Chris Dore, a consulting archaeologist and adjunct professor of anthropology with the University of Arizona, the use of aerial images for archaeological purposes began in the 1930s. Since then, commercially produced satellite images have become widely available and, thus, more cost effective to archaeologists.
In recent years, image resolution has greatly improved, and information that can be gleaned from images now ranges far beyond what can be seen by the natural eye to translatable data in the non-visible light frequencies—a collection process referred to as multispectral remote sensing.
One of the most difficult archaeological features to identify is a trail on which people walked or rode. Because the resolution in most aerial photos or satellite images is too poor, ground surveying is often necessary, and it takes an immense amount of time and personnel in the field. Dore, however, came up with a way to enhance data from multispectral sensing and tease out the telltale signs of trails, saving hours in the field.
LiDAR, or light detection and ranging, mapping is one of the most powerful new tools in topography. Precisely detailed surface data is collected using the reflection of laser pulses shot from an airplane flying in a sweep pattern. Information collected can distinguish relative surface differences of as little as one inch. Green bands of the light spectrum can be used for penetrating fairly clear water to measure the bathymetry (submarine topography) of bodies of water.
According to digital media specialist Doug Gann, a preservation archaeologist with Archaeology Southwest, LiDAR scans of Chaco Canyon, in New Mexico, are proving to be a very useful research tool. “LiDAR increased the archaeological visibility of features, like Chacoan roads, which can be identified with a high degree of accuracy and clarity,” Gann said.
In 2005, LiDAR datasets cost as much as $943 per square mile for projects as small as 50 to 100 square miles, to as little as $472 per square mile for projects larger than 250 square miles. Some airborne laser swath mapping datasets are acquired through a program of the National Center for Airborne Laser Mapping and sponsored by the National Science Foundation, to help graduate student investigators complete their research.
The University of California’s San Diego Supercomputer Center operates the OpenTopography.org portal where many of these datasets are compiled.
The Pima Association of Governments invested in a dataset that covers much of Southern Arizona. This information, purchased primarily for use by the Pima County Regional Flood Control District, is available, for a fee, to consultants and contractors, including those in the field of archaeology. The high cost of these datasets has led to cooperation among entities that would benefit from the shared information of a consortium.
LiDAR has proven very useful in archaeological areas with dense forests such as the jungles obscuring ancient Mayan features. As thick as the vegetation is, some beams will still penetrate between the canopy leaves, giving a detailed simulation of the forest floor, as well as the vegetation layers above that floor.
This information proved very useful to archaeologists such as the University of Arizona’s Takeshi Inomata, whose colleagues were able to glean vast swaths of geospatial information about Mesoamerican societies, without the impact and cost of extensive field surveys.
“It gives us detailed information on the distributions of house mounds, agricultural fields, etc., over wide areas,” Inomata said.
Likewise, LiDAR may help in places where subsistence agriculture now overlies large arrays of archaeological sites. And conflicts are less likely to flare up if local farmers don’t feel threatened by field archaeologists surveying an entire landscape.
Continuing to pioneer unexplored horizons, aerial photographer Adriel Heisey has, on several occasions, come upon geoglyphs and ruins that were previously unrecorded. He notes that sometimes features may be known by the nearest neighbors, but the features haven’t been documented as archaeological resources. Since online access to archaeological records has improved, Heisey is more easily able to determine which finds are previously unrecorded.
“The sense of discovery is sometimes intoxicating,” Heisey said of his multilateral devotion to flying, photography and archaeology. A massive exhibit featuring 60 of Heisey’s aerial photos is currently on display at the Arizona State Museum.
“It was a real treat for me to work with Adriel in selecting the photos that went into this exhibit,” said Bill Doelle, president of Archaeology Southwest. He points out that Heisey used a 21/4” x 3 1/4” format camera, so the images print well in a large format.
“People are excited to see ancient places and see them in a way they normally never could,” said Heisey.
“I began shooting out of the regular airplanes I was flying for my job and found it was increasingly frustrating because of the windows and the speed and the altitude and the angles, and just not being able to be there at the perfect time.”
He overcame these obstacles when he built his own airplane for the sole purpose of doing photography.
“It is an acquired skill to be able to recognize these features, many of which are quite subtle; they don’t just jump off the landscape at you,” admitted Heisey. “The light has a lot to do with it; the angle of the light and the intensity of it has a lot to do with how archaeological features will be revealed.
“You begin to recognize when things look unnatural, when something was made by human beings. One of our prime strengths as humans is our pattern recognition capabilities and that includes the ability to recognize something on the ground that wouldn’t have been formed by natural processes.”
Perhaps archaeologists working on the new horizons of advanced, technology- assisted scanning are learning to recognize information in ways that took Heisey years to develop.
The use of unmanned flying drones with cameras is on the horizon. Gann has documented some of the early drone efforts and posted videos on the ArchaeologySouthwest.org website, at http://tinyurl.com/mpfs95q.
However, the Federal Aviation Administration has not yet established regulations on the use of drones for applications such as research and photography, and is not expected to until 2015.
Meanwhile, Heisey will continue to make new discoveries. “In my line of work, you have to decide to really focus on the ancient. You can put a filter on your view to screen out things that are more obvious, more recent and more typical of our own civilization, and look for the things that have been there for many, many hundreds of years and are very, very subtle,” he said.
From Above: Images of a Storied Land is an exhibit at the Arizona State Museum located on the University of Arizona campus through Sept. 20,2014.
Claire Rogers is a local, freelance writer. Comments for publication should be addressed to firstname.lastname@example.org.
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