Drones are becoming more common place with particular uses in the military, geological mapping, and even entertainment. One team of researchers are using drones and LiDAR to map a former leprosy colony which is rapidly deteriorating in an attempt to preserve the site.

The Surprisingly Long History of Drones

When most people hear the word drone, they think of quadcopter RC aircraft fitted with cameras (and invading people’s airspace). However, drones—also known as UAV or Unmanned Aerial Vehicles— date back as far as 1849 where Austria sent unmanned, bomb-filled balloons to attack Venice.

As time progressed, many engineers and scientists developed unmanned systems in an attempt to reduce pilot deaths. The drone considered to be the first modern drone was the Israeli Tadiran Mastiff (1973) as it used a data-link system, streamed live video, and was used in battlefield scenarios. The turn of the 21st century has seen drone use shift from battlefield applications to more peaceful environments including mapping, entertainment, and even transportation of goods.

One application of drones that is proving to be of great help is in archaeology. But how do drones high up in the air help archaeologists study the past buried in the earth? This is where LiDAR comes in!

Drones are becoming more common and less expensive.

A Basic Intro to LiDAR

Without going into too much detail (there is a fantastic LiDAR article here), LiDAR stands for Light Detection And Ranging. It is very similar to how SONAR and RADAR, but uses light as opposed to sound and radio. Simply put, a LiDAR unit emits light towards an object of interest and measures information on the light that reflects back.

A sensor on the source detects the reflected pulse of light and measures the time taken between the emission and reception. Knowing this time (divided by 2), and the speed of light, the distance between the object and source can be determined using the simple yet powerful equation, speed = distance x time

This measurement between emission and reception gives the range of a point, which is not very useful when trying to generate an image. To gather more complex information, the emission source is directed very rapidly to create a scan line (akin to barcode scanners), which generates a line of distance data. If that scan line is swept across an area (such as a room), an entire “distance” image can be generated.

LiDAR rendering of a group of people. Image courtesy of NASA

Drones and LiDAR are becoming increasingly accessible and decreasingly expensive, especially in recent years. Such being the case, both technologies can now be found across a wide range of industries. Archaeologists and historians combine drones and LiDAR to identify and 3D-render historic sites.

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A Bird's-Eye View: Drones and LiDAR

Some historic sites are dead easy to find. It's somewhat difficult to miss the Pyramids of Egypt or the Leaning Tower of Pisa.

However, some sites that are just as important (historically speaking) are much harder to find. Some have been destroyed and some have simply been buried as time goes on. Finding them often relies on historical documentation which outlines the locations of sites, even though there's no longer an obvious visible structure.

This is where LiDAR steps in and illuminates the historical treasures that lie beneath the earth. Even if a historic building collapses and all of its structural materials are removed, one piece of evidence remains: the foundation.

Image courtesy of the Unit for Landscape Modelling (ULM) Cambridge University © Historic England

All buildings (past and present) have to be built on flat ground to help with structural integrity and to provide a proper ground floor. (Romans in particular love their tiled underfloor heating.) Since there are very few places in the world that have naturally-occurring, truly flat ground, the foundation leveling results in disturbing the ground which the building occupies. This disruption results in the building foundation being either lower than the surrounding ground or higher.

From the air, this change in height is often unnoticeable to the naked eye after hundreds of years. However, LiDAR can spot such changes with ease and it is this ability that archaeologists are exploiting. In the past, researchers could only attain high-level views of areas by hiring a plane or helicopter to carry LiDAR equipment. However, when LiDAR is coupled with drone technology, the cost of taking aerial shots of foundational evidence is much lower. This makes it easier and cheaper for archaeologists to search for undiscovered sites and learn more about the past.

But taking aerial shots of historic building locations is not the only task that a drone can perform in the field of archaeology.

Back Down to Earth: Sending Drones into Structures

One team of Australian researchers, the Robotics and Autonomous Systems Group at CSIRO, is using drone and LiDAR technology to map a leprosy colony on Peel Island, Australia. The site, which operated between 1907 and 1959, was a quarantined colony designed to house those with leprosy and prevent the disease's spread. The site consisted of many huts and structures, housing both patients and doctors.

Since its closure, the site has been a popular tourist attraction; but, due to safety concerns, entry to the structures is now forbidden. This is not due to concern over leprosy but rather due to the risk of structural collapse as the buildings have not been taken care of since the site's closure in 1959.

One of the drones tasked with carrying a LiDAR payload. Image courtesy of CSIRO.

In the interest of preserving the site, historians are using drones mounted with LiDAR equipment to not only map the site from above but inside the huts and structures as well. The goal is to create a 3D model which will preserve the site digitally so that when the elements finally destroy the site, a record of what existed will be around for future generations.

Summary

Historic sites have been lost for many reasons, from environmental conditions to disasters or even armed conflict. When such sites are lost, every generation that exists from that point onward loses out on a piece of our shared heritage. This is why digitally preserving such places is imperative.

Technology, if used correctly, can provide invaluable tools to help us explore our past. Mounting sensors and data gathering systems onto UAVs, which can explore environments too dangerous for people, not only helps to save lives but also helps with our understanding of our surroundings without fear.