Use of Thermal Imagery in Archeological Research
Abstract
Thermal imaging is a method of increasing visibility by detecting an object’s infrared radiation and creating an image from the information, (Rouse M. 2011). Thermal imaging has long been used by archeologists to locate buried architecture and various cultural landscape elements. However, it has still been a problem for archeologists in understanding the archeology of standing ancient structures. This is due to a challenge in uncovering plastered surfaces as they possess significant historic importance. Infrared Cameras attached to low-cost drones are used to study structures below the ground level without having to excavate first (Jesse C., Et al, 2017). It is therefore evident that thermal imaging has been extremely instrumental in archeological research (Brooke C., 2016). Passive infrared cameras have been found to be successfully used to study archeology of underlying plastered surfaces to detect man-made anomalies and building materials.
Use of Thermal Imagery in Archeological Research
Archeology is the study of societies and lives of people who lived in the past. It studies ancient civilization by recovery and analysis of remains from particular periods, environment and geographical regions. These include building ruins, burial grounds and monuments, human fossiils and artefacts (Maggs M., 2015). Archeoogy is a tool used to determine human history that was not recorded through writing. However archeology can also cover modern civilization up to present time. Archeology allows us to understand human history and look at human culture. Through it we understand how the culture has been shaped and how it has changed over time, how it has evolved and adapted to various environments and why these changes happened. It enlights us on aspects of development of agriculture, trade routes and cultural believes of the past.
Different methods are used by archeologists in the identification, excavation and processing of information obtained from the excavation process so as to deduce important information from the site findings. This information could vary from dating of discovered artefacts, deductions of conditions of the environment that impacted the artifacts to culture that may have impacted the artefacts. Archeology follows a series of steps before the actual excavation is done.
First a survey is carried out.Archeologists do not randomly start excavating random areas in search for archeological sites. The areas are first surveyed through various methods such as visual inspection to try and narrow down the area to excavate as precisely as possible. Remote sensing and aerial photography. Oral interviews are also conducted as a big part of history is passed dow generations through verbal delivery. These help archeologists narrow down areas to excavate but are not always accurate methods ("Methods of Archaeology," n.d.).
Once the area of excavation has been identified archeologists estimate a grid system to help them record the exact location from where artefacts are recovered during the excavation. Several test pits are then dug to determine the density and spread of the artefacts, again by mere estimation. Excavation then begins as archeologists note the precise locationnfrom which the artefacts are retrieved. The excavated dirt is also screened for any artifacts thst could hae been missed during the excavation. Archeologists also search for features during site excavation. A feature refers to evidence of human activities that has a vertical component and is immovable ("Archaeological Methods," 2015).
Once excavation is completed the discovered artifacts and recorded information is then processed and analysed. Methods of analysis include dating of the discovered artifacts as well as study of the structure and composition of the said artifacts and features. There are various methods used in study of structure and composition and dating of artifacts. Based on the type of artefacts archeologists could either employ relative dating methods or absolute dating.
Relative dating presumes age by comparison to other artefacts found in the vicinity of the artefact being dated. Therefore it is inaccurate and is on ly capable of placing an artefact in a time sequence rather than giving it a precise age. Some methods of relative dating include stratigraphy and style analysis. In stratigraphy items in the lowest layer are assumed to be older than the items in the preceding top layer. Style analysis associate certain styles and shapes with a certain historic period.
Absolute dating is highly dependent on scientific analysis and can provide age of an artefact precise to the year. Various absolute dating techniques include radiocarbon dating which is used to date organic matter, uranium-lead dating, luminescence dating and so on. The main limitation of absolute dating techniques is that they require destruction of atleast a piece of the artefacts that is used to conduct the dating or study the internal structure of features (Johnston, 2019).
These methods of both identification of archeological sites to processing of the excavated information have been found to be both time consuming, tedious and inaccurate. Archeologists have been forced to canvass large geographical areas only to find very small significant areas for excavation from their survey. A lot of resources both financial and in terms of labor are also used in the excavation processes as archeologists are unable to precisely pinpoint the sites where either the artefacts or features are located. Some artefacts and features also get destroyed if archeologists overcut their excavation while others remain undiscovered if the archeologists undercut during the excavation. These errors either lead to incomplete information being available for processing which in turn increases the margin for error of the deductions made from the information gathered. Artefacts and features also get partially deformed as parts are removed for the purpose of exploring their structure and age.
Recent scientific developments have allowed technology to reduce the margins of error involved in the archeological process either in the survey phase, the excavation phase or the information processing phase. The precisely introduction of Thermal imaging technology in archeology has allowed a massive step up for archeology as a field. Thermal imaging uses infrared emission from objects to generate images from the information.
Thermography which is also referred as thermal imaging is one of the methods that archaeologists are using today in a scientific investigation. The method involves the practice of translating the infrared radiation into the material under investigation. The science behind this type of investigation is that the method is simple but detailed. Any material that is hotter than absolute zero basically emits infrared radiation. The infrared radiation that are emitted by these materials makes them hotter. Thermal cameras have ability to access the infrared radiation that is emitted by such materials. The radiations are then translated by the cameras to thermogram or into thermal image.
Archaeologists have been using this method since 1970. The method is has been able to detect both exposed and subsurface remains. When the materials are heated by the sun rays during the day, they absorb the heat from the sun. During the night this heat is released into the atmosphere in the process of cooling. This happens at different rates depending on the material. The temperature release rate fluctuations are detected by the camera sensors for translation.
Although archaeologists are using thermal imaging, it is not the best. The method has however shown an improvement in terms of sensitivity and features of the imaging have improved. The cameras basically use fuzzy changeable pictures which are basically representations of the temperature. Therefore, coming up with a sensible information requires experts in interpretation. In experienced people can misinterpret the images specifically when the cameras provides scenario have extenuating situation like inclement weather or any other kind of interference. One of the disadvantages of using the method is that the capital that is required to set up an investigation station is expensive. In addition very experienced professionals are required to interpret the images produced by the cameras.
One of the common thermal imaging techniques that the archeologists are using is the new aerial thermography. The use of aerial thermography has ensured that archaeologist is able to gather field survey data over a wide area within a little time. Comparing the method with the older method, the older method could not record enough spectrum data or temperature data for a pixel image. The recent cameras are small and have ability to collect data of small object. The cameras are small which make it possible to be mounted on a drone to collect data while on air. The data collected through the aerial method is accurate and the information that is unreachable can be accessed easily with the help of a drone. The method has also facilitated mapping of multiple images with the help of photogrammetric software.
References
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Jesse Casana, Adam Wiewel, Autumn Cool, Austin Chad Hill, Kevin D. Fisher, Elise J. Laugier (2017). Archaeological Aerial Thermography in Theory and Practice. Advances in Archaeological Practice,; 1 DOI: 10.1017/aap.2017.23
