Since the astronomer and composer Sir Frederick William Herschel (1738-1822) discovered in 1800 the infrared portion of the electromagnetic spectrum, many other scientists became interested in this kind of invisible radiation. It lasted, however, until 1904 for the first near-infrared photograph to be taken. From the 1930s onwards, this unusual type of imaging was practised more elaborately, specifically to examine damaged and censored writings or study blood patterns for medical purposes. After 1935 – the year in which one of the earliest infrared aerial photographs was taken from a stratosphere balloon – the trend was set. Less than a decade afterwards, aerial infrared colour film became extensively used for its camouflage detection capabilities in WWII. Today, orbital and aerial NIR recording serves a great number of applications, being intensively used by the military as well as the scientific fields of hydrology, geology, forestry and archaeology. Up till now, NIR radiation was mostly captured in an analogue way by infrared sensitive plates or film emulsions (black-and-white or colour), or digitally by satellites or high-tech multispectral sensors. For various reasons (cost, resolving power, lack of hardware etc.), aerial archaeologists use(d) the analogue NIR approach to study their objects (some examples are – amongst others – the work of Bradford, Strandberg, Solecki, Edienne and Martin). Such a film-based workflow is however very error-prone, as the emulsions need to be stored cooled and developed by specialised labs directly after exposing them. Moreover, determining the right exposure is not as straightforward as with conventional/standard (i.e. visible light) photography. Together with some ignorance and/or lack of knowledge about the subject, this critical imaging process severely restricted NIR radiation to be captured by aerial archaeologists so far. However, this changed completely with the advent of digital cameras. As their sensors are very sensitive to NIR radiation, the whole process of taking NIR photographs is much less of a cumber stone. The poster under consideration wants to show how NIR imagery can be taken with normal (and converted) digital cameras, what the images look like, compare the advantages (and disadvantages) to normal aerial imaging (e.g. haze penetration, enhanced clarity of detail and visualization of stressed vegetation) as well as outline a basic approach of NIR image processing.

Please cite as: Verhoeven, G., 2015. Becoming a NIR-Sensitive Aerial Archaeologist. AARG 2007, 25 September 2015, Danish Heritage Agency, Copenhagen, Denmark. DOI: 10.5281/zenodo.165988