Monday, October 1, 2018

Seeing The Forest Without The Trees: Lidar Reveals Many Maya Ruins

We've known the the Maya civilization was populous and grand in its classical period. But, now, with Lidar, we understand its grandeur in a manner that was obscured by jungles over the centuries, in exquisite detail. 
Combing through the scans, Acuña and her colleagues, an international 18-strong scientific team, tallied 61,480 structures. These included: 60 miles of causeways, roads and canals that connected cities; large maize farms; houses large and small; and, surprisingly, defensive fortifications that suggest the Maya came under attack from the west of Central America. 
“We were all humbled,” said Tulane University anthropologist Marcello Canuto, the study’s lead author. “All of us saw things we had walked over and we realized, oh wow, we totally missed that.” . . .
Lidar’s principles are similar to radar, except instead of radio waves lidar relies on laser light. From an aircraft flying just a few thousand feet above the canopy, the surveyors prickled each square meter with 15 laser pulses. Those pulses penetrate vegetation but bounce back from hard stone surfaces. Using lidar, you can’t see the forest through the invisible trees. 
Beneath the thick jungle, ruins appeared. Lots and lots of them. Extrapolated over the 36,700 square miles, which encompasses the total Maya lowland region, the authors estimate the Maya built as many as 2.7 million structures. These would have supported 7 million to 11 million people during the Classic Period of Maya civilization, around the years 650 to 800, in line with other Maya population estimates.
From the Washington Post.

The introductory discussion of the source scientific journal article is as follows:
Reports of lost cities in the Maya forest began with the remarkable pictorial folios that Stephens and Catherwood produced from their journeys in the 1830s (1) and that inspired the Carnegie Institution of Washington's expeditions in the early 20th century (2). This research focused on major architecture: the grandest temples, plazas, tombs, and palaces built for Maya aristocrats. The singular attention paid to rulers illuminated Maya politics and religion but left a major lacuna in knowledge of the populace. To fill this gap, later fieldwork mapped the humble housemounds to interpret settlement patterns at the detailed site scale (3–5). On page 1355 of this issue, Canuto et al. (6) use a remote sensing method called light detection and ranging (lidar) to examine regional-scale settlement patterns and implications for sustainability in the Maya forest. Their conclusions support extensive settlement densities, as has been expected, and suggest substantial land modifications that affect assessments of sustainability.
Anabel Ford and Sherman Horn, "Above and below the Maya forest" 361(6409) Science 1313 (September 28, 2018). DOI: 10.1126/science.aav0887

The paper itself has this abstract:
Classic Maya civilization in detail 
Lidar (a type of airborne laser scanning) provides a powerful technique for three-dimensional mapping of topographic features. It is proving to be a valuable tool in archaeology, particularly where the remains of structures may be hidden beneath forest canopies. Canuto et al. present lidar data covering more than 2000 square kilometers of lowland Guatemala, which encompasses ancient settlements of the Classic Maya civilization (see the Perspective by Ford and Horn). The data yielded population estimates, measures of agricultural intensification, and evidence of investment in landscape-transforming infrastructure. The findings indicate that this Lowland Maya society was a regionally interconnected network of densely populated and defended cities, which were sustained by an array of agricultural practices that optimized land productivity and the interactions between rural and urban communities. 
Structured Abstract 
Lowland Maya civilization flourished from 1000 BCE to 1500 CE in and around the Yucatan Peninsula. Known for its sophistication in writing, art, architecture, astronomy, and mathematics, this civilization is still obscured by inaccessible forest, and many questions remain about its makeup. In 2016, the Pacunam Lidar Initiative (PLI) undertook the largest lidar survey to date of the Maya region, mapping 2144 km2 of the Maya Biosphere Reserve in Guatemala. The PLI data have made it possible to characterize ancient settlement and infrastructure over an extensive, varied, and representative swath of the central Maya Lowlands. 
Scholars first applied modern lidar technology to the lowland Maya area in 2009, focusing analysis on the immediate surroundings of individual sites. The PLI covers twice the area of any previous survey and involves a consortium of scholars conducting collaborative and complementary analyses of the entire survey region. This cooperation among scholars has provided a unique regional perspective revealing substantial ancient population as well as complex previously unrecognized landscape modifications at a grand scale throughout the central lowlands in the Yucatan peninsula. 
Analysis identified 61,480 ancient structures in the survey region, resulting in a density of 29 structures/km2. Controlling for a number of complex variables, we estimate an average density of ~80 to 120 persons/km2 at the height of the Late Classic period (650 to 800 CE). Extrapolation of this settlement density to the entire 95,000 km2 of the central lowlands produces a population range of 7 million to 11 million. Settlement distribution is not homogeneous, however; we found evidence of (i) rural areas with low overall density, (ii) periurban zones with small urban centers and dispersed populations, and (iii) urban zones where a single, large city integrated a wider population. 
The PLI survey revealed a landscape heavily modified for intensive agriculture, necessary to sustain populations on this scale. Lidar shows field systems in the low-lying wetlands and terraces in the upland areas. The scale of wetland systems and their association with dense populations suggest centralized planning, whereas upland terraces cluster around residences, implying local management. Analysis identified 362 km2 of deliberately modified agricultural terrain and another 952 km2 of unmodified uplands for potential swidden use. Approximately 106 km of causeways within and between sites constitute evidence of inter- and intracommunity connectivity. In contrast, sizable defensive features point to societal disconnection and large-scale conflict. 
The 2144 km2 of lidar data acquired by the PLI alter interpretations of the ancient Maya at a regional scale. An ancient population in the millions was unevenly distributed across the central lowlands, with varying degrees of urbanization. Agricultural systems found in lidar indicate how these populations were supported, although an irregular distribution suggests the existence of a regional agricultural economy of great complexity. Substantial infrastructural investment in integrative features (causeways) and conflictive features (defensive systems) highlights the interconnectivity of the ancient lowland Maya landscape. These perspectives on the ancient Maya generate new questions, refine targets for fieldwork, elicit regional study across continuous landscapes, and advance Maya archaeology into a bold era of research and exploration.
Marcello A. Canuto, et al., "Ancient lowland Maya complexity as revealed by airborne laser scanning of northern Guatemala" 361 (6409) Science eaau0137 (September 28, 2018) 
DOI: 10.1126/science.aau0137


Marnie said...

Thanks for this. It's especially interesting that with this technique, they can see smaller structures, such as dwellings.

I think we'll see a lot more of this, especially as companies like Aerovironment develop drone mounted high resolution lidar such as the Quantix with lidar.

Many archaeology projects don't have a big budget and the potential for archeaologsts to self fly their own reasonably priced high resolution lidar systems looks promising.

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