Rescue blankets hamper thermal imaging in search and rescue missions

Thermal imaging for unmanned aerial vehicles is used to search for victims in poor visibility conditions. We used a gimbal-mounted camera for thermo-radiation measurements of body temperature from persons covered with rescue blankets in the hibernal wilderness setting. Long-wave infrared radiation in the spectral range between 7500 and 13,500 nm was evaluated. Parts of this research have previously been published in a review on electromagnetic radiation reflectivity of rescue blankets (https://www.mdpi.com/2079-6412/10/4/375/htm). Surface temperature measurement was diminished by clothing, namely by 72.6% for fleece, by 82.2% for an additional down jacket and by 92.3% for an additional all-weather jacket, as compared to forehead temperature. Furthermore, we detected that a single-layer rescue blanket is sufficient to render recognition of a body shape impossible. With three layers covering a clothed body infrared transmission was almost completely blocked. However, rescue blankets increase visibility for thermal cameras due to high gradients in temperature. Conspicuously low temperatures from objects of 1 to 2 m length may indicate reflections from rescue blanket surfaces in a cold environment. Ideally, rescue blankets should be removed from the body to increase the chance of being located when using thermal imaging to search for victims in search and rescue missions.