THE ROLE OF REMOTE SENSING TECHNOLOGIES
The MAEASaM project will use remote sensing to identify yet-to-be found archaeological sites, to assess and monitor the preservation conditions and susceptibility to threats of new and known sites, and to predict future threats for heritage management planning. The MAEASaM Remote Sensing Working Group discuss the value of this approach.
Remote sensing is the science, the technology and the art of obtaining information of an object under consideration, without coming into physical contact with it (Lillesand et al. 2007). While our own eyes are remote sensing devices, they are limited to what we can see within our field of view and the light spectrum range – that is, the visible spectrum. A camera carried on an aircraft or a scanner in a satellite is like an extended eye: it can see an entire landscape at a moment in time, since it is orbiting above the earth and has been enhanced by sensors that capture light well beyond the spectrum visible to humans, into the ultraviolet and the infrared regions, for example. Since the advent of aerial photography in the late 1800s, this extended eye has been used to discover archaeological sites. Observing the earth from above is one of the best ways to find archaeological sites and understand archaeological landscapes, revealing features that are too faint or too large or too fragmented to be appreciated by an observer at ground level.
Left: Aerial photograph of stone-walling, southern Africa
Using remote sensing in Ethiopia has given me the opportunity to explore the country’s vast and diverse landscape in great detail. My work so far has used open source satellite imagery to analyse and monitor landscapes where known archaeological sites and monuments are located, including the UNESCO World Heritage site of Harar Jugol, the Fortified Historic Town located in eastern Ethiopia. The availability of Google Earth imagery in recent years has meant I can zoom into known areas of historic importance and see what is happening around them – for example, if there are any new urban developments in the area, desertification of the landscape or agricultural change, the opportunities are endless.
Nadia Khalaf, University of Exeter
A WIDER LENS
Not surprisingly, more archaeological sites are being discovered every year through remote sensing than by any other method. As an archaeological technique, it has many advantages, being non-destructive, cost-effective and relatively fast. Today it is used by archaeologists to find new archaeological sites in areas that have not been investigated before and that are difficult or dangerous to reach, also proving invaluable in monitoring many and varied heritage threats from looting to flooding.
New technologies, new perspectives
High-resolution multispectral, hyperspectral, Light Detection and Ranging (LiDAR) and synthetic aperture radar (SAR) satellite imagery have provided new perspectives for archaeological investigation, ranging from synoptic views to small details. Incorporating machine-learning techniques and algorithms that facilitate the automated detection of sites and features, together with multitemporal remote sensing big data, further extends the potential of remote sensing in archaeology.
We plan to use traditional techniques based on visual inspection but also to exploit the complementarity of multi-sensor, multi-polarisation, multi-band and multi-temporal remote sensing systems in combination with innovative machine learning approaches.
Right: Light Detecting and Ranging (LiDAR) imagery of stone-walling in southern Africa.
Left: Landsat imagery showing the archaeological sites of Harlaa and Harar in Ethiopia. Green pixels indicate the extent of urban growth.
- S. Merlo, MAEASaM Remote Sensing Co-ordinator and Project Manager
- A. Akintayo, Postdoctoral Researcher, Tanzania
- N. Khalaf, Postdoctoral Researcher, Ethiopia
- P. Ochungo, Postdoctoral Researcher, Kenya