Mapping a Legacy
March 1, 2009
The Canyon de Chelly National Monument is one of the most impressive archaeological resources on the planet. Located in northeast Arizona, this unit of the National Park Service encompasses 83,840 acres and is home to a community of Navajo people and an estimated 4,000 archaeological sites, which range in complexity from fields of ancient stone tools and pottery to 60-room pueblo dwellings.
The park was established in 1931 to preserve archaeological sites and items of scientific interest. Prior to that, there were frequent episodes of vandalism in the area. The Navajo Nation and professional archaeologists joined forces to convince the federal government to set aside the park as a national monument. “We have archaeological sites going back 5,000 years,” says Jennifer Lavris, an archaeologist who is surveying the canyon along with fellow archaeologist Keith Lyons. “It’s our job to locate and monitor the archaeological sites and make sure everything is taken care of.”
Organizing and researching such a plethora of archaeological sites demands accurate surveying data. “For virtually any research question we ask, we will need accurate spatial data,” Lyons says. “We want to know what resources they used, such as water and plant resources, and the locations of those resources.” The ancient tribes also created rock art, and the archaeologists need to locate it accurately. Long-range plans include GIS mapping of the park and its archaeological sites.
Control in a CanyonThe canyon is Y-shaped. To date, the archaeologists have established a network of 16 primary control points and 60 to 80 secondary points. Eight primary points are located about two miles apart on each side of the Y’s stem. “The secondary points are arbitrary points set at 500-meter intervals between each primary point,” Lavris says. “In the canyon, we can’t get good GPS data. The canyon is too confining. So by having a control network, we’ll be able to set up a robotic total station on any control point and shoot the location of any archaeological site [within range].”
To set up the network, Lavris and Lyons rented a Topcon Static/RTK GR-3 GNSS (multiconstellation) system. The primary control points are established with better than 2-centimeter root mean square (RMS) precision using a GPS static solution. To take satellite readings, the GR-3 unit is positioned over the control point for a minimum of two hours. After the hours have passed, the archaeologists and crews shut down the instrument, download the file and submit it to the Online Positioning User Service (OPUS) run by the National Geodetic Survey. Data are submitted 24 hours after it is collected, and OPUS returns the final processed coordinates.
“Once we have processed coordinates for the primary points, we can start setting secondary points using real-time kinematic technology,” says Mark Gonzales, a training specialist with Holman’s Inc., a Topcon survey equipment and GIS dealer in Tempe, Ariz. One of the GR-3 receivers is set on a primary point, and a radio link is established to the second GR-3 receiver. Using a Topcon FC-200 data collector and TopSURV software, the primary point is fixed to the base unit. The base transmits the correction to the rover using a UHF radio, and in real time the rover achieves 2 to 4 centimeters of precision. Gonzales says the secondary control points take about two to five minutes each to set using 150 one-second readings and a weighted average. “The TopSURV software does that all automatically,” he says.
In addition, the archaeologists bought a hand-held Topcon GMS-2 GPS data collection system to collect and record data points. The mapping-grade GIS-tailored system has an internal camera, and it enables the archaeologists to record attribute information about various points. “They can also use the GMS-2 to navigate and recover all their control points,” Gonzales says. According to Lavris, the hand-held GMS-2 field controller obtains the GPS and Glonass satellite signals and is capable of receiving 12 to 15 satellites on average. “Our maximum with other units has been seven satellites in some areas,” she says.
Mapping for the FutureTo map the ancient sites in detail, the archaeologists have purchased a Topcon GPT-9003A robotic total station. It comes with an FC-200 data collector with TopSURV 7 software. “We will tie into the control point network with the total station to have everything tied together spatially,” Lavris says.
She notes that the robotic total station enables one person to map an average-size archaeological site in one day. It locates vertical and horizontal coordinates and permits detailed maps to be produced. “The robotic total station ‘talks’ through infrared laser and spread-spectrum radio technology,” Lavris says. “You set up the machine to follow you, and when you want to record a point, you press a button and it finds you and shoots the point.” The FC-200 hand-held data collector is Bluetooth-enabled and has a keyboard to enter information about various points.
The archaeologists are also considering the possibility of conducting high-resolution scans of some of the archaeological sites using a Topcon IS Imaging Station. “They can take that scan, create a 3D model of the site and drape georeferenced images over that so that the model looks like the real thing,” Gonzales says. “That will document the shape of the wall’s structure as well as its texture and physical characteristics. And the archaeologists can take a detailed inventory of the rock art with that system.” According to Gonzales, the scans will allow changes resulting from forces such as erosion or vandalism to be monitored to better help NPS management protect the fragile sites.
In the same way that a GIS system can show a city where all the fire hydrants are, a GIS map can show the archaeologists locations of the rock art, plants or other resources. “All the data collected from the Imaging Station will go into a GIS map,” Gonzales says.
Entering Canyon de Chelly into a GIS database is a huge undertaking, but Lavris believes the effort will have far-reaching benefits. “We’re looking to map archaeological sites to very high detail with very little error,” Lavris says. “We’re looking 20 years into the future and beyond. This will set the framework for managing these resources from here forward.”
Sidebar: Reconstructing the Puzzle of the PastArchaeology has been a lifelong interest of Holman’s Mark Gonzales. As a student at Pima Community College Centre for Archaeological Field Training in Tucson, Ariz., Gonzales studied anthropology and archaeology. Gonzales later worked for the center as a staff archaeologist specializing in mapping excavations of sites inhabited by prehistoric cultures such as the Hohokam civilization in the Tucson area.
He also spent more than 16 years directing topographic and hydrographic surveying data collection under the direction of Glen Canyon Environmental Studies and Grand Canyon Monitoring and Research Center. These data were used in the preparation of specific scientific surveys in the Grand Canyon on the Colorado River for the U. S. Geological Survey and the U.S. Bureau of Reclamation. “My job was to develop a surveying and mapping program to monitor resources in the Colorado River ecosystem in the Grand Canyon,” Gonzales says. “That work included surveying and mapping cultural resources such as archaeological sites.
“It’s very difficult--and some people thought it impossible--to use GPS technology where there are steep canyon walls,” Gonzales says. “But with emerging technologies, I helped develop many methods to successfully map natural resources by combining GPS technology, conventional surveying methods and remote sensing technologies such as aerial mapping.”
Modern surveying and mapping technology enables archaeologists to ask and answer new spatially related questions for the first time, Gonzales says--questions such as, “How far did they go to get water?” or “How far did they go to get hematite to color their art?”
What’s more, modern surveying technology enables archaeologists to be far more precise than in the past. For example, when an archaeologist reconstructs a puzzle of an ancient living site, it makes a big difference whether a certain stratum can be measured to the nearest foot or to the nearest centimeter. “That foot may mean thousands of years of time,” he says. “But if we can measure it to the nearest centimeter, the puzzle of the past can be reconstructed more precisely.”
At Canyon de Chelly, the sheer abundance of historic artifacts and sites provides an incredible chance to combine archaeological efforts and advanced surveying technology. “There aren’t many opportunities to put together the whole story in the way that we hope to do at Canyon de Chelly with this mapping technology,” Gonzales says.