As you learned earlier in the course we use photographic methods that allow us to see beyond the human visible spectrum. In week three you saw this in terms of imaging landscapes where by capturing information reflected in the infra-red (IR) part of the spectrum or the ultra-violet (UV) we can reveal areas of the ground that are hotter and colder as a consequence of buried features such as walls. Our colleague Geert Verhoeven has pioneered the latter approach and also used infra red recording in flights above Portus.
We also use multispectral imaging on the ground. As with aerial photography the key component is a modified camera – cameras usually have the IR and UV removed via a filter within the camera. So, we use professionally modified cameras to allow this energy through, and then filters attached to the lens to block out the visible and any other parts of the spectrum we are not interested in. This allows us to be very precise about the wavelengths we allow through and hence capture in the camera specific materials and object properties. Our colleague Eleni Kotoula is an expert at using this technique for analysis of objects and in particular as part of the conservation process.
In addition to recording objects using multispectral approaches (sometimes including multispectral RTI capture which again has been pioneered by Eleni) we have used multispectral imaging to record writing within the surviving rooms at Portus. These data have not been analysed extensively yet but combine modern and ancient notes.
This is one of a number of photos taken in the rooms in the basement of the Palazzo Imperiale that record visits by people in antiquity and the 18th and 19th centuries © Geert Verhoeven, Department of Archaeology, Ghent University