Rescue blankets hamper thermal imaging in search and rescue missions
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Rescue blankets hamper thermal imaging in search and rescue missions Markus Isser1 · Hannah Kranebitter2 · Andreas Kofler3 · Gernot Groemer4 · Franz J. Wiedermann5 · Wolfgang Lederer5 Received: 3 April 2020 / Accepted: 23 July 2020 © The Author(s) 2020 OPEN
Abstract Thermal imaging for unmanned aerial vehicles is used to search for victims in poor visibility conditions. We used a gimbalmounted 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. Keywords Emergency medical services · Infrared rays · Insulation · Rescue work · Rescue blanket · Thermography
1 Introduction Rescue blankets are essential components of first aid equipment used by hikers and alpinists in outdoor sports [1, 2]. Blankets are composite materials and consist of a polyethylene terephthalate sheet coated with a thin aluminium layer with a surface colour of silver or gold on either side [3]. While the polyethylene terephthalate sheet provides high tear resistance [4] and diminishes heat loss from thermo-convection and evaporation, the aluminium layer protects against hypothermia by reflecting infrared (IR) radiation back to the body [5]. Manufacturers recommend turning the silver facing towards the source, e.g.
silver side down when aiming to block thermal radiation from the body and silver side up when protection against an external source of heat is desired [6]. As the metallic surface flashes in the sun, it increases a victim’s visibility for search and rescue (SAR) services. The silver side of the blanket is highly reflective, but gold up may be more conspicuous in a snow and glacier environment [7]. The use of thermal imaging in unmanned aerial vehicles (UAVs) is increasing in popularity with rescue organizations and fire brigades [8, 9]. Especially in SAR missions and firefighting, non-contact thermal imaging devices are being deployed more and more
