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The Petén, Guatemala

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The Petén, Guatemala
Ground-Truth Information

Mayan Research challenges: collecting ground-truth information

Our intrepid explorers in a stand of treesGround-truth information, often referred to as "reference data," involves the collection of measurements or observations about objects, areas or phenomena that are being remotely sensed. This ground-truth information can be used by social scientists in two ways: first, the data can aid in the interpretation, analysis and validation of the remotely sensed data; second, such information helps in understanding the socioeconomic forces behind land cover modifications due to human activities.

Clearing the road of trees Ground-truthing is expensive and time consuming. In recent years, the cost of computer hardware and software for remote sensing analysis has dropped dramatically, however; the costs associated with ground-truth activities have generally escalated. Airfare, lodging, vehicle rental, food, labor, and the like remain expensive elements of the research activity. However, recent advances in affordable GPS receivers and digital data field recorders allow the researcher greater flexibility in the sampling design.

The terrain is
so difficult even a burro gets stuck in the mudIn order to have an accurate, and sufficiently large reference data set, we have to visit as many sites as possible in the remote and rugged terrain of the Petén. Frequently, we break camp each day and move on to the next location. This is in contrast to the approach used by others who remain at a site or village for an extended period. We never excavate archeological features, we strictly map and verify their existence. Some challenges encountered while conducting fieldwork in the Petén include logistical problems, communication problems, equipment failure, inadequate maps, physical stress, suspicion, danger, and unstable political environments. Our research team once was captured and held at gunpoint by leftist guerrillas for several hours before being released at nightfall.

Not all roads are dryLogistics are probably the major constraint on our fieldwork. Often we are the first professionals to visit an unrecorded archeological site. A logistics coordinator is used to schedule in advance the jeeps, boats, aircraft, mules, horses and workers that will get us to our destination. Since many areas of the Petén do not have telephone service, a member of the team who lives in Guatemala must travel weeks and months in advance to arrange the rentals with the local villagers. The more inaccessible the location, the more difficult the arrangements. Once the logistics have been coordinated, the field missions last two to three weeks. As the mode of travel switches from jeeps to boats to horses and mules, it is critical that the dates, times, and locations for these arrangements be finalized in advance. Exacerbating the logistics are the difficult conditions sometimes encountered in the road and pathways. These conditions include downed trees, and extremely muddy paths.

Educating local residents aids our research goals and objectives Occasionally, we are met with suspicion regarding the true purpose of our research. We have successfully combated this situation by taking the time to educate the local residents about our research goals and objectives. We always take a large number of satellite images and, after explaining how we are using the imagery, leave a copy of it with the person(s) involved. We have gained acceptance and support for our data collection activities, and the confidence of the inhabitants through years of exposure and word of mouth, and are even known to the locals as the "Traveling Wilburys," which came about because of the single cassette tape of the recording artists the Traveling Wilburys that was taken on a field activity. As the years have passed, many of the inhabitants have become sufficiently educated about satellite imagery and GPS units, that when we stop at a village and present the images, they can often help us interpret some of the displayed features and anomalies. Having a Guatemalan national on our research team has been a positive benefit to our research activities.

Obtaining our position with the aid of a GPS unit GPS measurements are a critical component of our field research. In 1988, when there were few satellites in orbit, and the receivers were not as sophisticated, we often found ourselves climbing a temple at midnight to collect a position that would only be available between 1 and 4 am. Also, in the tropical rain forest, the dense vegetation cover attenuated the GPS signals. Today, with the complete constellation of satellites, the readings can be gathered nearly around the clock. More sophisticated GPS receivers and software are available that allow for the collection of more data with greater accuracy. Even with all the technology, there are still hazards to collecting GPS information. In the tranquil scene to the left above, what is not shown are the two jaguars which have crept onto a tree limb above us.

Determining our position with the aid of villagers A problem often encountered is the inaccuracy of available maps. Consistently, we find that lakes, rivers, archeological sites, and cultural features are not located where the map indicates. Apart from the obvious in-field confusion, there is the major concern that if these inaccurate maps are digitized and incorporated into a GIS, they will lead to false results for predictive models. This dilemma is resolved by constant comparison of GPS measurements, imagery, and maps to eliminate as much confusion as possible. Also, the names indicated on the maps are not necessarily the same as used by the local inhabitants.

A five star restaurant in the jungle As we studied deforestation trends in the Petén over the last several years, we designed our ground-truth activities primarily to identify the difference between new forest clearings and regrowth. We are now expanding our activities to include information on the decision processes on land use and land conversion. We are in the process of interviewing local farmers and ranchers to address the scientific issues of deforestation rates and trends in land use conversion to understand the uncertainty involved in modeling the terrestrial carbon budget. Through the interviews, factors such as crop-to-fallow ratios, the decision process for converting land to pasture or shifting to agriculture, forest fragmentation indices, spatial characteristics of cleared land, associated socioeconomic factors will be determined. These results will be correlated over the time scale of our database, providing better analytical information for management decisions.

Responsible Official: Dr. James L. Smoot (
Page Author: Tom Sever
Page Curator: Diane Samuelson (