Airborne laser scanning is often used to prepare for new construction, but a recent study in Guatemala used the technology to understand some very, very old construction.
LiDAR is an active remote sensing technology that uses laser pulses to create a 3D map of ground land cover and ground surface in three-dimensional space. Two years ago, Guatemala’s Pacunam LiDAR Initiative (PLI) embarked on the largest-ever survey of the Maya Biosphere Reserve, collecting data on 2144 km2(827.8mi2) of ground. The researchers hoped that their survey would provide more data on the ruins of an old Maya lowland settlement located on the territory.
A LiDAR system collects data by sending quick light pulses at the ground, and using a sensor to measure pulse return. Using differences in return time and return wavelength, scientists can map out 3D images of the underlying terrain. In this case, the PLI used a Titan MultiWave multichannel, multispectral, narrow-pulse width LiDAR system. According to parent company Teledyne Optech, it’s the first airborne LiDAR sensor to capture data in multiple spectra. Its standard configuration measures visible spectrum RGB light, near-infrared (NIR) light, and intermediate infrared radiation, which provides a more complete picture of ground under cover.
The initiative was the most advanced LiDAR system deployed in the region to date, scanning the terrain from six angles as opposed to the usual two, and capable of recording in higher resolution. The team was able to collect 33.5 billion laser pulses, and received 5.2 billion ground returns. On average, the team got between 1.1 and 5.2 ground returns per m2 (10.8 ft2), a difference explained by variations in vegetation coverage. From those returns, the researchers were able to create a bare-earth terrain model using geographic information system (GIS) applications, including ArcMap, QGIS, GRASS 7.2 and the Relief Visualization Toolkit.
For some of the terrain, the researchers were able to check the accuracy of their results. With 7.7 percent of the survey region already “ground-truthed” (ground-surveyed either before or after the airborne study), the researchers were able to estimate the accuracy of the remaining survey area.
The researchers used their map, and the understanding of the ruins they could gain from it, to draw conclusions about the settlements. Their survey showed 61,480 ancient structures in the region, with wetland farmland, farm terraces in mountainous areas, causeways stretching between sites, and defensive features like walls up around them. From that, they were able to make population estimates, learn more about how the region’s agriculture was organized, and make educated guesses about the sociopolitical order that existed at the time.
The team is excited about the possibilities that LiDAR might bring in the future, both for this site and for the field in general. The team’s paper concluded: “These perspectives on the ancient Maya generate new questions, refine targets for fieldwork, elicitregional study across continuous landscapes, and advance Maya archaeology into a bold era of research and exploration.”
To read the original Science article where the findings were published, see here.