Avalanche rescue using ground penetrating radar

Every year world-wide, over 150 people are killed by snow avalanches. Method of rescue statistics show survival is best when skiing with a companion (69% survival) and having something stick out of the snow after burial like an avalanche cord or ski (72%) followed by use of personal radio transceivers (40%). Organized searches (16% survival) using probe lines (12%) and search dogs (11%) take time to assemble. Victims only have a 30% chance of survival after the first hour of burial, and only 35% if buried deeper than 1 meter. Ground penetrating radar (GPR) could provide an efficient method for locating buried avalanche victims. Snow is an excellent propagation media for GPR waves. A human body is highly conductive with a high dielectric permittivity contrast relative to snow, serving as an ideal reflector target for GPR. However, it has been unknown how GPR will respond to the unfavorably changing dielectric properties as a body freezes. It is also unknown whether or not GPR can distinguish a human body from other natural and man made objects in the avalanche debris field. A human body mass equivalent (BME) was buried in snow, and the GPR response and core temperature were recorded versus time as the BME froze in a simulated avalanche burial at a cooperating ski area. A freshly euthanized pig was used as the BME, due to the similarity in properties to that of a human body. The experimental measurements show that it takes about 110 hours for the 145 pound BME to completely freeze while buried in snow with an ambient temperature of -7degreesC. Throughout the course of the experiment, the BME could be uniquely identified relative to other buried natural and man made objects by its imaging GPR signature. Modeling showed this was a consequence of a unique phase shift from constructive and destructive interference occurring in a thin layer sequence at the BME-air-snow interface. This resulted from initial body heat melting of snow, development of a thin air pocket, and subsequent refreezing. Thus, GPR has the potential to image, identify and locate a human body and therefore possibly save lives, or at a minimum, help recover the body before spring thaw.