Over the past decade, there has been a silent revolution in archeology, virtually allowing archaeologists to see through the ground without digging. Advances in geophysics, soil chemistry and remote sensing are accelerating the discovery of ancient sites and helping archaeologists understand them on a global scale.
Below is our list of the top six of these techniques. While each has value in their own right, the future will lie in their combination, perhaps one day creating a virtual reality linked to GPS that will take the observer underground.
While you won’t find actual artifacts this way, and you can’t date what you see, this approach is much more durable than digging and risking damage to things. Instead, it leaves the archeology buried for future generations when excavation techniques could be even better.
1. Google Earth
Satellite imagery such as Google Earth, Microsoft’s Bing, and NASA’s World Wind have made it possible to zoom into even the most remote corners of the globe to locate sites. By helping to spot features such as settlement mounds or enclosures, it can help draw attention to places where such sites can be found. Aerial photographs have been used in this way since the 1930s, but they were generally difficult to access. The universal availability of Google Earth has therefore made it a fantastic tool for professional scientists and citizens alike. However, there are many pitfalls in interpreting satellite images that can only be resolved in the field.
Archaeological sites often leave superficial traces of what is buried under the ground. We have long worked to manually map the elusive “bumps and bumps” often using hatching, a form of representation invented in 1799. Now, Light Sensing and Range Finding (LIDAR) technology produces detailed three-dimensional maps of light. Earth’s surface in a fraction of the time. . In principle functioning as a tabletop scanner but operated from an airplane, the laser beams are directed towards the ground, while being connected to an accurate GPS and an inertia measurement system, generating a cloud image of points on the ground surface. One of the advantages of LIDAR is that it can often see through vegetation, locating sites otherwise obscured by woods or rainforests.
Archaeologists have used drones for several years to capture sites from the air. Before that, we used a variety of homemade kites, helium balloons, and model airplanes – filling the gap between aerial photographs and images taken from the top of landrovers and shaking ladders. Drones can take photos in low light conditions and in frost and snow conditions when archeology can be best viewed. A particular application is to mimic LIDAR, taking overlapping vertical images, and with ground control (usually paper plates at fixed points) it is possible to generate point cloud images in three dimensions, using standard software packages. In the not too distant future, it will be possible to mount LIDAR directly on drones.
4. Shallow geophysics
Geophysical techniques can help locate targets to be studied. Soil resistivity, for example, is a measure of the resistance of the soil to the flow of electricity. It can uncover differences in soil moisture to reveal buried structures and can reliably reach up to around 1.5 meters deep. However, it is slow because probes have to be inserted into the soil at regular intervals, but it can produce very detailed results. Magnetometry measures the strength of the earth’s magnetic field. This may reflect the pattern of archaeological features created either by burning or by soil bacteria that can leave magnetic traces in the soil. It is a quick technique and has been shown to be particularly effective for desert sites, such as in ancient Egypt. Recently, sensitive multi-sensor magnetometers, mounted on a cart and linked to a GPS, are able to survey many acres in real time per day and reveal entire landscapes, like those around Stonehenge.
5. Soil geochemistry
Traces of human and animal dung around ancient settlements can remain in the soil for millennia. It has long been known that by recording heavy metal patterns in the soil, it may be possible to locate these ancient sites. This is especially important if there are few or no artifacts left. One way to perform such measurements is to take samples and analyze them in the laboratory. But in recent years, portable X-ray fluorescence spectroscopy (pXRF) meters have become available, allowing rapid recording of samples in the field. They work by emitting x-rays which the atoms in the sample absorb. This increases the energy of the atoms, which in response emit secondary x-rays to a single energy that reveals the elements of which the sample is made.
6. Ground penetrating radar
When ground penetrating radar, which uses radar pulses to image the ground, was first applied to archeology in the early 1980s, it was believed to be the answer to many problems in archeology. But as the technology gradually improved, archaeologists weren’t impressed. The early use of such a radar produced sections through the deposits. However, there were countless cases of false positives. Recently, software has come to the aid of technology, enabling three-dimensional modeling, making visualization much more reliable. One of the advantages of ground penetrating radar is that it works in confined spaces and through hard surfaces. But the interpretation of the results remains a problem. Be very skeptical of hidden Egyptian tombs and Nazi trains.