GPS signal reception under snow cover: A pilot study establishing the potential usefulness of GPS in avalanche search and rescue operations

摘要

Avalanches are one of the major threats to life in high-mountain terrain and account every year for approximately 150 accidents causing injury or death in the United States alone. Every year avalanches cause significant property damages and a death toll of approximately 1.5 people in the United States. The specific characteristic of the avalanche accident is the extreme importance of getting to the buried victim as soon as possible to improve survival. Approximately 40% of all buried victims survive 1 hour, and only about 20% survive 2 hours. Newer studies from Europe indicate that the initial survival probability is 92% at 15 minutes, 30% at 35 minutes, 27% at 90 minutes, and finally drops to 3% at 130 minutes. Unless prompt and efficient search and rescue are ensured, the prospect of buried victims is rather grim. Many tools have been used in the past to aid in retrieving buried victims including the avalanche cord, probing techniques, and in more recent time, the use of electronic beacon devices that allow search teams to locate the buried victim. The advent of satellite navigational aids (GPS, GLONASS) makes it possible to determine one's position with remarkable accuracy. We studied the degree to which the GPS satellite signal could penetrate through snow and be received by a commercially available GPS receiver. This information may lead to the development of an additional tool for precise and quick localization of buried victims in avalanche accidents and thus may substantially improve their survival by shortening the search time at the accident site. In this study we used a Motorola Traxar six-channel GPS receiver with amplifier unit connected to an antenna by means of a shielded coaxial cable. The antenna was buried under incremental covers of compact snow, and the reception of the GPS signal was measured at each burial depth: 5 cm, 15 cm, 25 cm, 35 cm, 45 cm, 55 cm, 1 m, and 1.5 m. The variables that were measured included signal quality, number of satellites received by the receiver, and their respective signal strength. A reference reading was taken from the GPS receiver above the testing site before measurements under snow cover were started. The satellite signals were received with good quality and precise readings up to a burial depth of 1 m. Under 1.5 m of snow the receiver was able to lock on only one satellite, making a positional reading impossible. The reception of the GPS signals under snow cover is possible and warrants further study directed toward the development of a search and rescue device using this technology.