thermal

The Heat is on! Drones and Thermal Cameras in Archaeology

Lunch views at Zagora

Lunch views at Zagora, Greece

My name is Hugh Thomas and I am an Australian archaeologist who specialises in remote sensing and digital methods in archaeology. Simply put, I specialise in different photography techniques, both terrestrial and aerial, to both record and discover new archaeological remains.

This post will be about a project I directed during May and June of this year called the Zagora Infrared Photogrammetry Project (ZIPP). This project, which was funded by an Australian Government Endeavour Research Fellowship, was conducted under the auspices of the University of Sydney and the Australian Archaeological Institute at Athens.

The ZIPP Team

My project used drones to create large, 3D models using both regular light and infrared cameras(more commonly known as thermal cameras). The idea behind using thermal cameras is that as the temperature starts to drop, like at dusk, the ground will begin to cool. Any archaeological remains that exist under the surface may radiate heat, or absorb heat from the nearby ground, which will cause the dirt around it to cool at a different rate than the wider area. The hope is that your thermal camera will pick that difference in temperature.

Thermal image. A small rectangular feature, probably the foundations of a small building.

We also use regular photographs to create 3D models of the areas so we can see if any thermal irregularities we have found can be explained by something sitting on the surface ie. grass or rocks.

https://p3d.in/G8NFN

 

Click this link to interact with a 3D model of Zagora.

This thermal imagery technique has been around since the 1970’s but it is rarely used, because until recently, people had to use aerial photography platforms like helium balloons and the cameras were not particularly great. But with the popularity of drones and the reduction in cost of thermal cameras, this type of remote sensing should become more popular.

So I proposed a project called the Zagora Infrared Photogrammetry Project where I, along with some volunteers, would spend 6 weeks performing this work at an Early Iron Age site called Zagora. I have a long history with Zagora. I was a trench supervisor for excavations there in 2012-2014 and was their digital specialist. Zagora has a really interesting history. We don’t know when it started, maybe 900 BC or perhaps earlier, in a period of Greece just after the big Bronze Age civilisations had disappeared. The site, which sits on a promontory on the west coast of the island of Andros, seems to have survived until about 700 BC, when is was abandoned. Thankfully for us, the site was never resettled, apart from a small temple that seems to have been maintained. This has meant that the town naturally collapsed, and was never damaged by later buildings. This is rare for sites of this period, so we are incredibly lucky.

Thermal image of the Archaic temple

So what does a day look like on ZIPP. Unlike most archaeological work which starts early in the morning, we often only left for site at 3-4pm. As Zagora is so remote, it would take us around 30 minutes to walk to the site from where we leave the car. In order to prepare an area for aerial survey, we would lay a series of cardboard crosses around the area under investigation. These were then shot in with a very accurate, RTK based GPS system, that has an accuracy of around 2cm.

Emma Williams records a ground control point with a RTK GPS system

The crosses act as ground control points and allow us to geolocate the area we are photographing. We then fly the area with a regular photographic drone. This is designed to create a 3d model of the area to act as a control to any thermal images we take.

Orthophotograph (an output of 3D modelling) created with drone images.

We generally would do this for two or three areas in each session. Then we would have to sit and watch the sun set, which is a pretty nice way to work.

Once the sun had set, and the ground began to cool, we would place on head torches and begin to photograph the site with the infrared camera. This is incredibly daunting, especially as you are flying in the darkness with equipment that is worth thousands of dollars. Each area would be flown once, normally for a period of around 15 minutes. Then we would pack up and walk the 30 minutes back up to the car. Towards the end of the season, we wouldn’t be back to the car until 10:30 at night. As it was so late, any night we did thermal work, we would run down to a local taverna for a quick meal. It is an incredibly exhausting form of work and it is not pleasant walking up mountain tracks in the pitch darkness.

Walking home in the dark

The next morning, we would all slowly wake up and after caffeine, we would begin to process the work from the night before. This involves analysing hundreds of photographs, making 3D models and trying to identify thermal anomalies. ZIPP was a fantastic success. We found over 60 different thermal signatures, from drains running through roads to massive housing complexes. In some areas we could see the internal and external faces of walls.

This image shows a room, the walls are showing up as warm(white) lines. You should hopefully be able to see a colder(black) square area in the center, which is the internal part of the room.

Ultimately, every feature discovered will be placed into a report for the excavators of Zagora and the Greek archaeological ministry. The directors  will analyse the results and we will determine which features should be the focus of excavations in the future.

Hopefully this highlights a different form of archaeological investigation and emphasises how useful non-destructive techniques can be.