ARCHAEOLOGICAL MAPPING ISN’T WHAT IT USED TO BE

Various technological advancesVarious technological advances are making the job faster, are making the job faster, easier, and more accurate. easier, and more accurate.

By Reed Karaim

The cutting edge of archaeological mapping comes wrapped in an unimpressive silver box. With a diabolically winking green eye visible through a small glass window, it looks like something out of a bad 1950s’ science fiction movie. On a rare gray morning in Tucson, the box is perched on a tripod above a 2,000-yearold pithouse, blinking away quietly while Jim Holmlund, president of Geo-Map, an archaeological and geological mapping firm, monitors its progress on a laptop. “You should see it in the dark,” Holmlund says while we wait. “You see all these flashes of green laser light—thousands of them. It’s really quite beautiful.”

The 3-D laser scanner sits on tripod in preparation of scanning a pithouse at the Rio Nuevo site in Tucson, Arizona.

The three-dimensional laser scanner finishes its work. The computer screen starts to fill with dots,and what’s revealed is beautiful enough to any field archaeologist.A pointillist image of the pithouse takes shape.There is more processing of the data to be done back in Geo-Map’s offices,and the end result will be a three-dimensional map of the pithouse accurate to within roughly two-hundredths of an inch.

On site,the entire process has taken no more than an hour. There are no string measurements,no laboriously calculated sketches on graph paper, no more hours kneeling in the dirt.“It’s quicker, and it’s incredibly more precise than the hand-drawn maps we would have had to do otherwise,”says Jonathan Mabry of Desert Archaeology, a contract archaeology firm in Tucson.Mabry is supervising the survey.“You’re going to see a lot more of this in the future.It’s going to revolutionize things.”

The laser scanner may be more Buck Rogers than Star Wars in appearance,but it’s the latest of a new wave of technology that’s transforming mapping.This new equipment “is going to change the way we do archaeology,”says Steven Shackley, an archaeologist with the Phoebe Hearst Museum in Berkeley, California.The technology includes global positioning systems (GPS),the latest generation of hand-held computers,and sophisticated software packages known as geographic information systems (GIS). These advances allow for unprecedented accuracy and detail as well as other remarkable capabilities.

THE PITHOUSE MEASURED BY GEO-MAP’S SCANNER scanner was part of the archaeological investigation undertaken by Desert Archaeology for Tucson’s ambitious Rio Nuevo redevelopment project.This site just west of the city’s downtown contains both historic and prehistoric occupations,including 4,000-year-old pithouses that show evidence of maize and pottery use.The data from the laser scanner provides “such a detailed record it allows us to rebuild the site in three dimensions back in the office,”says Mabry.

The scanner works by rapidly bouncing laser beams off many thousands of—often more than a million— points on an object.By measuring the differences in the infinitesimally small time it takes each laser beam to bounce back, the system is able to fix each point in space. The scanner measures at a rate of a thousand points a second.Holmlund says a scan of a typical pithouse has about 1.5 million points defining it.

At Rio Nuevo, the process starts with mapping specialist Joe Nicoli placing a handful of targets resembling Ping-

THE PITHOUSE MEASURED BY GEO-MAP’S

Pong balls on the pithouse floor.A digital camera built into the scanner then takes a picture of the site.The scanner operator, who controls it from a laptop computer connected by a cable, uses this picture to aim the scanner.Then the laser goes to work. The machine then scans in columns, moving from left to right,with these targets serving as reference points as the various sections of the map scan are integrated.The first pointillist image that takes shape on the laptop’s screen is raw data called a point cloud.

The point cloud data then undergoes a complicated process through which it is converted into information that archaeologists can understand and use.It includes registration of the scans, referencing them on a grid,and purging them of unwanted data.The scans are then used to create a model of the site that can be manipulated in various ways for various purposes through the use of different types of software,such as AutoCAD.

We see the end result of all this at Geo-Map’s offices. Nicoli,sitting at a desktop computer, calls up a map from a different site.A model of a pithouse rapidly takes shape on the screen. With a few mouse clicks,he moves the image forward and sideways.“We can get surface area, elevations, volume measurements,and profiles,” he says.“Archaeologists can play with the models and get all the measurements they want out of them.”

Shackley worked with Geo-Map last summer at McEuen Cave,a rock shelter in the Gila Mountains of southeastern Arizona that was inhabited between 2,200 and 4,000 years ago.Geo-Map is providing a three-dimensional re-creation of the rock shelter as well as all the features in the site,including two rocks covered with mortars.“They took millions of data points,” he says.“We’ll be able to reconstruct our excavations down to a centimeter (of accuracy) or less.”

Such a 3-D model can also be programmed to show the types of artifacts and features found at a site,the context they were found in,as well as the site’s stratigraphic information. With the inclusion of artifact, feature,and stratigraphic information, these models can serve as virtual replicas of the site.If, as sometimes happens,a site was investigated and then backfilled because a road or building was built over it, archaeologists could continue to study the site’s virtual replica.

The scanner has also been used to record features such as rock art.It’s able to measure the intensity of reflection of each laser pulse,which is shown by the intensity of the colors.“For rock art,” Holmlund says,“we can differentiate and accentuate small differences in patina values and paint color.”

Geo-Map has been mapping with the scanner for almost two years,and Holmlund believes his company is one of the very few in the United States consistently using this kind of equipment for archaeology. Part of the reason is the cost of the system.Geo-Map’s scanner goes for $150,000.Support equipment,software development,

Jim Holmlund, President of Geo-Map, Inc.

A laser scanner was used to map this Cienega-phase pithouse at the Rio Nuevo site.

Archaeologist and mapping specialist Joe Nicoli of Geo-Map, Inc., places scanning targets, which resemble Ping-Pong balls, in the pithouse.

Joe Nicoli examines newly acquired scan data in field.

An overview of 3-D model of two pithouses. The colored objects in the center of the large pithouse are digital “caps” placed over three floor features. The tops of the features must be closed in order for their inner dimensions to be measured.

This 3-D model of a pithouse was taken from the Rio Nuevo site. Measurements such as length, width, and depth of the pithouse floor features are taken directly from model. Archaeologists use these statistics to help analyze and categorize these structures. This is the underside of the pithouses shown in the photograph to the left. Measurements are being taken on various attributes of the floor features seen at the bottom of the pit.

The topography of the Cienega-phase pithouse is seen in this computerized image. The trench that cuts through the pithouse is clearly visible in the upper portion.

An enlarged view of a portion of a 3-D model of McEuen Cave in southeast Arizona. The protrusion in the center of the image is a boulder inside the rock shelter. The top of the rock shelter is directly above the boulder. The uneven nature of the floor is the result of displaced dirt from holes dug by looters.

hardware and software testing,training,and maintenance can cost as much as an additional $125,000.“The learning curve is tremendous,”says Holmlund.The laser scanner was originally used to develop 3-D models of offshore oil rigs.Steve Ahlgren,Geo-Map’s software specialist, worked for several months to develop some of the software that enabled the scanner data to be adapted to archaeology.

Despite the considerable expense of equipment and training,when the time and labor required for a handdrawn map is taken into account,Holmlund claims scanning is about two-thirds as expensive as the old-fashioned method.Mapping firms in Europe have reportedly started working with scanners,and Holmlund believes that a few other engineering companies have begun to test the use of scanners for archaeological applications in the U.S.

AN 1846 MAP OF THE WESTERN UNITED AN 1846 MAP OF THE WESTERN UNITED States hangs on Steve Baumann’s wall at the National Park Service,Western Archaeological and Conservation Center in Tucson.It’s a beautiful example of the old art of map making: rich in style,but short on detail and accuracy.The technological advances in mapping can be observed on Baumann’s computer screen.The topographic map of the area around Glen Canyon Dam in Arizona has none of the charm of the map above, but,with a few clicks of a mouse, it offers just about everything else an archaeologist could want.

The map is part of the center’s Integrated Cultural Resources Databank (ICRD),a geographic information system that allows park service staff easy access to an unprecedented amount of data about the archaeological sites

These are laser scans of a petroglyph found at a rock art site in Tucson. The uppermost small photograph shows the rock in which the petroglyph was pecked. The pecked image reflects the laser’s beam with greater intensity than the surrounding rock surface, and the laser measures this reflection. The result, as shown in the three other photographs, is that the petroglyph image can be separated from the rock. Researchers usually record petroglyphs by photographing and/or drawing them. Both of these methods, due to factors such as human interpretation and irregular rock formations, can be imprecise. A laser scan, however, allows for precise identification and measurement of rock art images.

they manage.The system is utilized by archaeologists at 12 National Parks in California,Arizona, Texas,Nevada,and Utah.It took three years to bring the first,Amistad National Recreation Area in Texas,on-line.Much of the effort went into fine-tuning software and scanning thousands of pages of field notes and photographs.In about nine months twice as much information was digitized for Glen Canyon,a park nearly three times larger.“It’s faster now because we know what we want to do,” Baumann says.

Starting with an aerial view in which each inch equals 100,000 feet,Baumann clicks his mouse for a closer view. Polygons begin to appear on the map,each identifying an archaeological site.He chooses a site, slides over to a dropdown menu,and suddenly we’re looking at field notes. “You can drill down from the polygon to the database to the actual report,and from there to any specific page or drawing or photograph,” he explains.

Earlier,we had visited the kind of file room where all this information has traditionally been stored—a windowless space with gray cabinets full of boxes holding pages and pages of typed reports,hand-drawn maps,and old photographs. Besides eliminating the laborious processing of digging through those files,the ICRD devised by Baumann and others also makes it easier to spot patterns and relationships across large geographic areas.

“It’s one thing to think about 10 sites in a specific area,”says Joe Labadie,an archaeologist and manager of the cultural resources program at the Amistad National Recreation Area.“But to try to do that with a great number of places across 50 miles—it’s beyond our analytical abilities.This system makes it easier to see the bigger picture, because you can move in and out and from one site to another so quickly.”

The Amistad Recreation Area includes a reservoir with 540 miles of shoreline on which there are more than 2,000 archaeological sites.The reservoir’s water levels can

rise or fall up to 60 feet in year, which makes Labadie’s job particularly challenging.But the Amistad ICRD, which integrates global positioning coordinates and contour maps of the lake beds, makes work along the constantly shifting shoreline much easier.For example,he says,if the water level falls 20 feet,he can use the GIS to quickly identify what sites will be exposed along the new shoreline that could be attractive to looters. “Park rangers can’t be everywhere,”Labadie says,“so GIS modeling allows us to target specific areas along the shoreline for ranger boat patrols so the most important sites can be protected.”

The database can be accessed through a hand-held computer.“I can drive out anywhere into the lake,stand on the shoreline with the (global positioning system), and if there is an archaeological site in the immediate vicinity, it will show me,”Labadie says. Baumann notes that conditions in the field often force archaeologists to adjust the day’s plans.The portability of the GIS makes such moves easy.“You’re not lugging file cabinets out there,” he says, “We’ve just got a couple of CDs with all the information we need.”He experienced the wonders of the system firsthand when he was working in Amistad and got lost. “All those canyons started to look the same,” he says, laughing.“We pulled the boat up to a shore,took a GPS reading, pulled the map up on the laptop with the site we were looking for, and said, ‘Okay, we’re a couple of canyons down.’”

Currently, the cultural databases for Amistad and the other parks are on hard drives and CDs.But the system should be on the Park Service intranet within a year, Baumann says. In the future,a move onto the Internet seems inevitable.

ARCHAEOLOGISTS EMPLOY GPS HAND-HELD UNITS units in survey work to establish the boundaries of a site and fix its location on a map. GPS, which is also used in rental cars and for recreational purposes,utilizes a signal from a satellite above the earth to identify the location of the system’s operator.This technology is generally accurate to within a range of one to five yards, depending on the model.A few companies,such as Geo-Map,are using a much more sophisticated system called Real-time Kinematic GPS,which provides measurements accurate to within half an inch. Such systems are not common in archaeology, Holmlund says,because they’re expensive— “tens of thousands of dollars”—and because many state laws require the technical expertise of a licensed surveyor to supervise their operation.

“GPS data generally has to be corrected and adjusted,” he observes.“These corrections involve understanding geodesy, cartography, and surveying principals.” Holmlund stresses that “it’s important to understand the theory behind the technology as well as the technology itself.”This is especially true for the more sophisticated GPS units, some of which can also incorporate data about artifacts found at a site.This information is then imported into a GIS program.

Shackley, Holmlund,Baumann,and others believe the latest advances in mapping should make detailed information much more broadly available.Digital recreations of archaeological sites and artifacts could also result in a certain amount of fieldwork being conducted,of all places, in front of a computer screen. This,among other things, could reduce wear and tear on sites,helping to preserve them for future generations.By eventually placing this type of information on-line,where it’s widely accessible, it could spark additional interest in the science.“This may be one way that the public has greater access to archaeology,” Shackley says,“and that would be a good thing.”

A 3-D model of bell-shaped pit superimposed upon a stratagraphic unit.

ARCHAEOLOGIGISTS EMPLOY GPS HAND-HELD Should an archaeologist want precise measurements of the various stratagraphic layers, this information can be obtained by manipulating the model to “explode” the unit. REED KARAIM is a writer living in Tucson. His work has appeared in the Washington Post, Fortune, and U.S. News and World Report.