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Telephone monitoring is in full swing in the search for those missing in the avalanche. It is one of the most important tools of the police. However, if the phones are covered with clay or parts of the house, the signals are not picked up.
Mobile phone tracking is one of the police’s most important tools in locating where people are in the avalanche. Photo: Hans O. Torgersen
The mobile phone must be switched on to use this technology. On Wednesday night, the police warned people not to call the mobile phones of the missing persons. They want to prevent phones from running out during follow-up work.
Professor Josef Noll from the Department of Technological Systems at the University of Oslo explains how to search for the mobile phones of people missing in the avalanche:
– The mobile phone periodically connects to the network and finds different bases. It can also send a signal to an area that the mobile responds to, he says.
– You can do this from one direction, or you can use the advanced cross mirror by sending from multiple directions.
Professor Josef Noll from the Department of Technological Systems at the University of Oslo believes that advanced mobile phone tracking has brought about a revolution in the search for missing persons. Photo: University of Oslo
– The same principle is used in dummy base stations, so-called IMSI receivers. Then the mobile will try to connect to them instead of the usual base stations.
The police have stated that they use these IMSI prisoners.
An IMSI receiver does not have a directional antenna. It will send signals in all directions. An antenna that points directly to the area will be able to better identify where the mobile is.
– But I don’t think the police use such directional antennas in this search, says Noll.
Police have said they can locate where the phones are with 20-25 meters of room for maneuver with the equipment they use.
With the help of advanced algorithms, GPS and time coordination, more precision can be obtained when searching for mobile phones. All the way up to a distance of two to three meters.
– This coordination works best stationary. The movement in the helicopter makes it difficult to coordinate the different bases, he says.
Noll says the problem with IMSI receivers is that they also want to trap other nearby mobiles that could interfere with communication.
– I don’t know how many IMSI sensors the police use at the same time and if they are coordinated.
Clay can stop the signals
Noll says the biggest challenge in this search operation is that the mobiles may be covered in clay or parts of collapsed houses.
– We know that mobile phone signals do not arrive in avalanches of only half a meter with densely packed snow, he says.
– That is why skiers who go to areas exposed to avalanches use special avalanche finders. They transmit at lower frequencies and the signals arrive.
Noll believes that the Norwegian police are used to using tracking technology when searching for missing people in the mountains.
– They have the necessary aids and can use them. The police are likely to be fully up-to-date with technological advances. It has meant a revolution in search operations, he says.
