The LiDAR system: a new vision for archaeology

16/06/2021

LiDAR stands for Laser Imaging Detection and Ranging), which translates as "laser image detection and ranging". In practical terms, it is a surveying technique using laser scanning. This technology started in the 1960s when the laser beam was invented; but it became a reality 20 years later, when the use of the Global Positioning System, better known as GPS, was commercialized. This technological tool is used for the generation of high-resolution maps, which are used in a wide range of studies ranging from commercial to military and scientific.

Among the scientific areas that make use of these images are the Earth Sciences, such as geology, geography, meteorology and geophysics; astronomy; biology, which uses it for a wide variety of studies that include aspects of diversity conservation, among others; and, of course, archeology. In this article I will focus only on its usefulness in archaeological studies, the importance of its use and the advances we have had in the discipline, thanks to the application of this technique. To do so, I will first explain how the system works.

Like many of the technological developments that we have today, the Lidar system is a tool made up of different technologies adapted to a single device. In this case, it consists of the laser beam, the GPS, and the inertial navigation system or INS. The device made up of these three tools is located on the outside and underneath of any type of aircraft, such as an airplane, a light aircraft, a helicopter, or even an unmanned aerial vehicle, known as a drone. However, there are also terrestrial devices.

The Lidar allows calculating the distance from the device, through the laser beam pulsed by the system, which can emit a large number of pulses per second, to any object or surface. Once the beam makes contact with the target, it bounces off and returns to the device, giving the distance between the two points. The coordinates of the objects and the different heights at which the pulses made contact can also be calculated.

Once the data are obtained, they must be processed with specific computer programs, through which the final result is obtained: a highly detailed image of the area covered by the aircraft. This image is known as a Digital Elevation Model (DEM).

The National Institute of Statistics and Geography (INEGI) has a collection of freely available digital elevation models at a scale of 1:10,000 of some regions of the national territory. Initially, and as we will see later, these models can serve as images with which we can begin to work and later focus on particular areas with the intention of generating models with a higher resolution.

What is Lidar useful for and how does it benefit archaeology?

3D surface images are a great help for archaeologists to identify and interpret archaeological sites, landscapes, and the way people or societies may have interacted with their environment. Since 1980, archaeology has used this type of model, such as DEMs or DTMs (Digital Terrain Models), to carry out research in Mexico and the world. Previously, aerial photographs were used, then satellite images and land survey methods such as total stations or 3D laser scanning. However, none of these methods or models allowed the elimination of information such as the thick jungle of the Maya area, which covered the objects of interest such as the settlements of extinct societies.

Lidar offers this advantage, giving us an image of the bare earth, without those trees that cover the vestiges of past cultures and that we could not observe with the naked eye or with models made with previous techniques. The major applications of the system, in Mexico, have focused on the Mayan region (little work has been done in other areas, such as the Gulf Olmec), which has allowed us to advance our knowledge of settlement patterns, road networks that connected the large cities and the way they exploited the resources of their environment, among others. Likewise, it has been possible to create three-dimensional models of entire cities, as is the case of some sites located in Belize.

Another advantage of the technique is the great time savings. For example, at the archaeological site of Caracol, Belize, it took archaeologists 20 years to survey an area of nine square kilometers. With Lidar, 200 km2 were mapped in just six days, and with a much higher resolution than when done on foot.

One of the latest archaeological projects to emerge from the discovery of a settlement through a low-resolution DEM, by the way from INEGI, is the Middle Usumacinta Archaeological Project (PAUM), led by archaeologists Takeshi Inomata and Daniela Triadan of the University of Arizona.

With the central objective of examining the emergence of the Maya civilization and its interaction with the Olmecs in the Mesoamerican Preclassic period, PAUM began its research work in 2017. This focused on a site that had not been previously recorded, Aguada Fénix, Tabasco; same that was located in a region of great relevance and of which were known, mainly, Classic settlements.

As part of the pre-production of the PAUM and based on the INEGI DEM, a high-resolution Lidar survey of the area of interest was carried out. The data processed and represented in the models yielded unprecedented information: 21 ceremonial centers with a standardized spatial organization were identified. In addition, it was possible to identify a massive human construction 1,413 m long on its north-south axis, almost a kilometer and a half, the equivalent of almost 12 soccer fields aligned along its length! In its east-west axis, its length is almost 400 meters.

Several things are striking about this great construction. The first is that, despite its size, it has not been identified in the surface surveys carried out in previous works in the area. But having had the opportunity to be there, I must confess that if they do not tell you that you are standing on the structure, you think you climbed a small hill 15m high. In this case, had it not been for the help of Lidar technology, we would still be unaware of the existence of Aguada Fénix. 

Consequently, the excavation work started in 2017 has begun to yield valuable information that begins to take shape and make sense of the relationships that were established between the aforementioned cultures, being able so far to obtain dates that place this large settlement around 800 BC.

There is still a lot to know about Aguada Fénix, but there is also a lot of territories that Lidar technology has to cover in our vast territory and, thus, offer us images of the earth's surface modified by humans for the development of their societies and communities.

By Claudia I. Alvarado Léon, Source INAH Morelos Center