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Show the melting point will only melt from any added heat. In the case of cold snow, disturbance of the temperature field by presence of the victim as a heat source theoretically ought to be detectable. In practice, any such effects might take hours to become recognizable with normal instrumentation. Even more severe is the problem raised by initial temperature inhomogeneities and the strongly disturbed avalanche debris snow. Heat conduction does seem to be a likely means of locating the victim. 2.6.4 Gravitation The human body is approximately three times denser than cold, dry avalanche snow. Under ideal conditions a highly sensitive gravimeter might be able to detect a gravity anomaly resulting from presence of a buried victim. Gravity measurements are slow, require a skilled operator, and the equipment is very expensive. At best, the victim could be detected only under ideal conditions, for local terrain anomalies would dominate the gravitational field in most cases. 2.6.5 Chemical Odor The avalanche dog successfully uses this principle, so it is known to work. No mechanical contrivance has yet been assembled which can duplicate the nose of a good dog. But the proven feasibility of locating victims by chemical odor suggests that this might be a more profitable avenue of investigation than the ones previously described. A sensitive detector of local carbon dioxide concentrations has been proposed as one attack on this problem. The method offers some possibilities, but no equipment has yet been produced for operational tests. A recent military device which reacts in very sensitive fashion to the ammonia in human perspiration might also merit tests for avalanche rescue. 2.6.6 Reflected Sound The sonar principle widely used for undersea detection might work in avalanche debris. A sound signal emitted at the surface would generate reflections from density or surface character variations within the snow, including a victim's body. Limitations on this method include the very short ranging distance, strong absorption of sound by snow, confusing reflections from natural inhomogeneities in avalanche debris, and the well-known difficulties of coupling appreciable amounts of sound energy into snow. 2.6.7 Reflected Electromagnetic Radiation Most parts of the electromagnetic spectrum are unsuitable for use in snow. Ultraviolet and infrared ( see 2.6.2) are strongly absorbed over very short distances. Visible light penetrates a long distance in snow, especially in the blue part of the spectrum, but is so strongly scattered by the snow crystals that buried objects are completely obscured by an inch or two of snow. Satisfactory transmission is possible in certain regions of the radio spectrum, so the radar principle could be applied in theory to locate a victim. The very short distances involved in avalanche search require pulse 50 |