For hundreds of years, maybe even thousands, humans have been digging holes, trying to unearth treasures of a bygone age. It is a messy affair, lots of shoveling and moving large amounts of dirt or sand. When it gets down to it small trowels may need to be used or even little brushes. How do we know where to dig? Well sometimes there are already existing structures, or the remnants of buildings. There could also be a building that has been there a long time. We just have to find hints that something interesting is under the ground. Archaeology can find things like pottery, tools and coins, but also parts of old structures. The problem is that more often than not these things are buried, else we would already know about them. In recent years archaeologists have used remote sensing methods to have a basic look underneath the ground before they dig it up. Basically the devices send a signal into the ground and see what gets reflected back. This can be very time consuming, moving equipment to a random field and spend all day setting up and getting reasonable measurements. Now with the increase of satellite technology there is a new way to look for new sites.
The method of using satellite imagery, such as that found on Google Maps, is generally referred to as an aerial survey. Traditionally this was done using cameras attached to an airplane, balloon or UAV’s. People have also been known to use kites! These pictures can be useful to help map a large area, or a site that is particularly complex. Plus if they are taken fairly often then they can be used to document to progress and status of the dig. This angle of image can also help to detect things not obvious from the ground. Things like different coloured soil/sand, or locations of certain types/colours of flowers can hint at a buried structure or wall. When solid rocks develop under plants they tend to grow slower, so a wall may actually be fairly obvious if looked at over time. Certain plants such as ripening grain changes colour rapidly, and if anything slows it down then it is noticeable compared to the other grain. When looking at different times of day the shadows could show areas of a field that are slightly raised from its surrounding.
With more and more Earth monitoring satellites going up all the time, companies like Planet Labs can now offer a satellite image of a specified part of land with updated images in the days and sometimes hours timescale. There have also been changes in the type of satellite going up, they are no longer just taking standard images. Modern technology allows the use of sensors seeing different wavelengths of light. The different bands of the electromagnetic spectrum can tell us different things about the thing you are looking at, and most of the spectrum, the human eye cannot see. Most of these satellites are designed to be used to look at weather conditions, specifically things like clouds and effect on the ground. Many modern weather satellites use microwave sensors to probe the ground. Much like microwave radar used to track airplanes, the satellites can send a signal towards the ground, and the signal that gets reflected back can say plenty about the surface. This is similar to the way ground penetrating radar works. SAR (Synthetic Aperture Radar) satellites are an example of this technology. There is also a good portion of satellites with Infrared spectrum sensors. This band is often giving data on aspects like temperature, showing how different sections of land are reacting to weather conditions can say plenty about what the ground is made of. There are also other methods to map the surface, such as LIDAR which is used in range finding applications, showing distances from the satellite to the ground.
Even though this is a fairly new technology for archaeology, there have been some significant uses of it. One of the most prominent uses have been to study the Maya civilization in ancient Mesoamerica. A particular area of interest is the Petén region of northern Guatemala. Very dense forest, and little to no modern settlements in the area make it difficult to study. Remote sensing has allowed scientists to study potential causeways and canals used by this early civilization. There have also been hints at cisterns and temples and buildings that they may have lived in. This allows for archaeologists to have a much better idea of where to look, without ever having to visit the jungle. In Peru, a group of Italian scientists have been getting results using satellite imagery. They have managed to get images of a buried settlement, including a pyramid in a riverbed. The North of Peru has also been known to be a haven for clandestine excavations. Satellite data has been useful to map and monitor archaeological looting. There have also been attempts to find lost cities such as Iram of the Lost Pillars in the Arabian Peninsula. The researchers found interesting information on old trade routes and uncovered a previously unknown settlement. There is also an award winning TED talk by Dr Sarah Parcak on using citizen science to search for sub-surface remains, Using normal people looking at satellite images they have prospectively found several significant sites in various parts of Egypt and the ancient Roman Empire.
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