Investigating Ancient Cities
Digging and archiving are still a part of modern archaeology, but it now includes state-of-the-art technology.
Modern archaeology involves more than digging around a site and recording what and where artifacts were found. Today, it involves sophisticated methods of surveying, analyzing, and record-keeping.
Important modern techniques are those collectively referred to as “remote sensing.” These methods allow an archaeologist to gather information from a site without actually digging, and can include aerial, satellite, and ground-based techniques.
Aerial imagery—taking pictures of a site from an aircraft in flight—provides archaeologists with a perspective of a site not available from eye level, and can sometimes reveal features not visible from the ground. Additionally, access to some areas may not be possible on foot. Aerial imagery can be obtained using a variety of aircraft, including satellites, airplanes, helicopters, balloons, and unmanned vehicles or drones.
Aerial photographs may be taken from the vertical or from oblique angles. Vertical photographs are taken directly over a site. There are no distortions in perspective, but it is can make details, such as differences in height, difficult to read. Photographs taken from oblique angles (not from straight above) allow archaeologists to spot elevation changes and give a perspective that complements a vertical photograph.
It should be noted that visible light is only part of the electromagnetic spectrum. Detection of infrared radiation—or heat—differences on a site can also lead to insights. Archaeologists sometimes make use of color infrared film and Thermal Infrared Multispectral Scanners (TIMS). Color infrared film is film that is sensitive to the infrared spectrum; it makes otherwise hidden details visible and is particularly useful in detecting vegetation. TIMS detect temperature differences near the ground.
For example, TIMS was used at the Anasazi site in Chaco Canyon, New Mexico, United States. The site is home to one of the largest concentrations of pueblos in the Southwest and includes many large stone buildings. There, TIMS detected a network of roads that were invisible to the naked eye.
Archaeologists may also use synthetic aperture radar (SAR) systems, which beam radar waves to the ground (from moving sources like airplanes or satellites) and detect the reflected energy, using it to create images. SAR systems can be used to detect linear features on the ground. The SAR system aboard the space shuttle Endeavor detected ancient watercourses in Sudan in 1994, which may help explain the origin of the “Great Bend” of the Nile River.
Other remote-sensing techniques, which can be used closer to Earth, include ground-penetrating radar (GPR), magnetometry, and Multi-Frequency Domain Electromagnetic (MFDEM) analysis. GPR systems send electromagnetic pulses into the ground and use the returned echo to determine an object’s depth; this can be used to create a three-dimensional survey of a site. Magnetometry systems, or magnetometers, measure differences in magnetism, and can be used to detect underground objects. They are particularly useful in discovering areas where fires—such as hearth fires— have occurred in the past, because fires affect the magnetism of topsoil. MFDEM systems generate electromagnetic fields to detect buried features of a site and can help archaeologists prioritize certain underground layers of a site. In 2012, MFDEM was used in Kabri, Israel, at the site of a Canaanite city dating from 2,000 B.C.E. At that site, MFDEM allowed discovery of a previously unknown underground chamber filled with jars.
One technique that can be used either from the air or on the ground is Light Detection and Ranging or LiDAR. LiDAR systems shoot lasers at surfaces and measure the reflection to create images. Air-based systems can be used to measure the heights of trees, ground features, and the like. For example, in Cambodia, LiDAR systems have been used to penetrate the vegetation at Angkor Wat (a Buddhist temple built in the 12th century under the Khmer Empire) and create highly detailed three-dimensional maps of the site. Ground-based systems can be used to provide accurate three-dimensional reconstructions of site structures. LiDAR was also used to reconstruct the Kabri storeroom with millimeter accuracy.
For ground-based surveying of a site, a device called a “total station” or “total station theodolite” is used. It was originally developed by civil engineers to measure the horizontal and vertical distance simultaneously. It allows an archaeologist to survey topographical features of a site and create maps designating the location of objects therein. For example, a total station was used to survey the site of Tell es-Safi, a city in modern-day Israel, which is thought to have been the home of the biblical giant Goliath.
Once a site has been surveyed, it can be examined and artifacts found there can be analyzed; even small slivers can be analyzed to yield important data. Two devices used for this analysis are an X-ray florescent spectrometer and a Fourier transform infrared spectrometer.
The X-ray fluorescent spectrometer is a device that resembles a supermarket checkout scanner; it has a large handle, trigger, and a display. It emits an X-ray that interacts with the atoms in an object. Depending on its composition, it will fluoresce at different energy levels. These levels are detected and used to identify the element.
A Fourier transform IR spectrometer makes use of the principle that when infrared radiation (IR) impinges on an object, some is absorbed by the object while the rest is transmitted through the object. The spectrometer detects the amount transmitted, which represents the molecular signature of the object, allowing it to be identified. The Fourier transform IR spectrometer is a device about the size of an inkjet printer, or about half the size of a milk crate. Small samples are placed inside for analysis at a dig site.
Although spectrometry can determine the composition of an object, it cannot determine how old an object is. To do so, archaeologists use carbon-14 dating. This uses the known rate of decay of carbon in formerly living items to determine an approximate age.
Not surprisingly, today archaeologists use handheld devices and laptop computers to record data found on site. Depending on whether an adequate internet connection is available, they can instantaneously disseminate the information to colleagues far afield.