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Why do archaeologists care?

Why multispectral imagery is relevant to archaeologists

As you’ve now seen, we can create spectacular pictures using multispectral imagery – but what use is this to archaeologists? In this step we’ll show you how it can be very useful in all three of the fields we highlighted in week one: prospection, landscape archaeology, and heritage protection.

Archaeological prospection

It might come as a surprise, but multispectral imagery can be really useful in helping to detect archaeological sites. This is because the soil that makes up archaeological sites is often different from other soils in the immediate area. This results from the activity of the people who lived there in the past, which can change the nature of the local soil, by altering its physical properties through the incorporation of materials like domestic rubbish, ash, animal dung, and decayed mudbrick and other building materials. These archaeologically distinct soils may show up well on imagery that uses non-visible wavelengths of light. Ploughed tells (settlement mounds) are a great example of this – the broken-up soil that arises from broken-up mudbrick, looks quite different from the surrounding agricultural land, which should more closely reflect the local ‘natural’ soil.

True colour northeast Syria Multispectral northeast Syria Notice how the archaeological sites (highlighted by the white outlines) in the true colour composite of Tell Leylan (above) in north-eastern Syria are much clearer in the false colour composite (below). The watercourses are also much more visible too. Can you see any other possible sites? Sentinel-2 (4/3/2 and 12/8/3) images, courtesy of ESA.

Wetland archaeology is another fantastic example of how multispectral imagery can be used for site prospection. Water, dry land and vegetation react very differently to infrared light, which makes false colour imagery a great way of finding sites rise only slightly above a surrounding marsh.

True colour Iraqi marshes Multispectral Iraqi marshes You can barely see a few raised sites in the true colour image of the southern Iraqi marshes (above), but the archaeology is much clearer in the false colour composite (below). Can you see the small pale mounds, and even some of the trackways radiating out from them? Sentinel-2 (4/3/2 and 8/4/3) images, courtesy of ESA.

Multispectral imagery can be a fantastic tool for finding new sites, but this is not always the case. How useful the technique is will depend on the nature of the archaeology and its environmental context!

Landscape archaeology

The aim of landscape archaeology is to better understand a site by incorporating its relationship with the local environment into our analysis. Multispectral imagery is a great tool for this! We have already seen how it can be used to better understand the distribution of vegetation, water, and soils and geology – which are all variables we are likely to consider when exploring the wider landscape.

Multispectral image of Wadi Qadisha This false colour infrared composite of Wadi Qadisha high-up in the mountains of Lebanon helps contrast the mountains with the more fertile valleys. How would you expect the archaeology to differ in these two areas? Sentinel-2 (8A/4/3) image, courtesy of ESA.

Multispectral image of northern Egypt Northern Egypt contains many different contrasting landscape types within a small area. You can imagine how sites will look very different in the Nile Delta and the Sinai desert. Sentinel-2 (12/8A/4) image, courtesy of ESA.

Heritage protection

Multispectral imagery offers a wonderful tool for monitoring archaeological sites and for tracking threats to heritage. Agriculture, urbanisation and mining are three obvious examples of the kinds of developments that can threaten archaeology that can be highlighted readily using multispectral imagery.

Multispectral image of Giza Urbanisation around the pyramids at Giza. The urban spawl is the purplish colour which now lies to both the east and west of the pyramids The sun is shining from the southeast, and so the monuments themselves are emphasised by the areas of shadow on their western sides. Can you see the dark triangles? Sentinel-2 (12/11/4) image, courtesy of ESA.

Multispectral image of Samarra Agricultural (and urban) expansion surrounding part of the UNESCO World Heritage Site of Samarra. Samarra was a short-lived capital city of the Abbasid caliphate, and its remains are spread over 150 sq-km of landscape to the east of the Tigris River, north of Baghdad. Sentinel-2 (8/4/3) image, courtesy of ESA.

Multispectral image of northern Oman Modern copper mining in northern Oman, obliterating any traces of the first Bronze Age mines. Oman supplied large quantities of copper to Southern Mesopotamia during the third millennium BC. Much of the evidence from this period has now been destroyed with large areas of the landscape, visible as purple blobs, being mined in the last forty years. Sentinel-2 (12/11/2) image, courtesy of ESA.

Are you more likely to make use of multispectral imagery for site prospection, landscape archaeology or heritage protection? Tell us about it in the comments below.
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Advanced Archaeological Remote Sensing: Site Prospection, Landscape Archaeology and Heritage Protection in the Middle East and North Africa

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