Using ground-based thermography to analyse surface temperature distribution and estimate debris thickness on Gran Zebrù glacier (Ortles-Cevedale, Italy)

In this study ground-based thermal infrared imaging was used to obtain surface temperatures distribution and to estimate the thickness of supraglacial debris on a mountain glacier. The study area is the eastern tongue of Gran Zebrù glacier (Ortles-Cevedale group, Central Italian Alps, Italy), having an area of about 0.23 km². The glacier surface includes some areas completely covered by debris. 
We used a FLIR E85 Thermal Camera to take 17 thermal images of the glacier surface on 30 September 2019, the images were taken from a distance of about 100 m from the glacier front. The thermal images were combined into a single panoramic image and calibrated in order to obtain surface temperatures. In addition, we manually measured the debris thickness and took thermal images at 18 points on the glacier, in a sector with a continuous debris cover. From these data, an exponential equation correlating measured debris thickness and debris surface temperature was obtained and applied to the panoramic thermal image to estimate debris thickness at each pixel with surface temperature > 0 °C.
This method allowed us to obtain the distribution of surface temperatures and of debris thicknesses with a high spatial resolution, between 0.11 and 1.10 m. The obtained surface temperatures show a spatial variability, ranging between -10.7 and 26.4 °C, with a mean of 5.8 °C. Snow and ice have mean temperature of -1.2 °C, while the debris cover a mean temperature of 14.1 °C. The estimated debris thicknesses have an inhomogeneous distribution on the glacier, ranging between 0.03 and 0.51 m, with a calculated mean debris thickness of 0.14 m in the areas completely covered by debris, that is in good agreement with field data.