Thermal-infrared measurements of the north-east tower at Ardrossan Castle

Thermal infrared imaging of buildings is used to investigate a range of phenomena including the accumulation of moisture. In general, the presence of moisture poses a direct danger to historic structures and must be characterised prior to any intervention. Many low-cost imaging solutions are available which has made the technology more accessible. In the current work, thermal infrared imagery (10~μm) of a likely gatehouse in the northeast corner of Ardrossan Castle (North Ayrshire, Scotland) was obtained by a multi-disciplinary team including academics and volunteers from a local heritage charity. Raw image data were processed to enhance the clarity of the images and included corrections for thermal drift and sensor uniformity. An image-stacking procedure was applied, and the images were analysed to determine their signal-to-noise ratio. The processed thermal images (temperature maps) showed evidence of moisture retention within the masonry system of the gatehouse. In addition, a small difference in temperature was observed between masonry and mortar, consistent with the expected behaviour of historic lime mortars. This approach has revealed new information, unknown from visible surveys of the castle, and was achieved using low-cost materials and freely available software. The impact of water ingress on historic structures is discussed, together with complementary remote-sensing technologies that may benefit further investigations at the castle and other historic stone structures.