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FMCW radars

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Frequency modulated continuous wave radars (FMCW) are buried into the ground, under the avalanche, in three locations along the avalanche path (see fig. 2). The radars are situated in pairs, 10 m apart, so that a cross-correlation may be carried out to find the flow velocities. The analysis of the FMCW radars allow the determination of

  • internal speed profiles,
  • front velocity,
  • avalanche flow heights
  • and erosion.

Each radar sees a vertical cross section through the avalanche during a defined period of time. Fig. 1 shows a typical output after elaboration of the signal. Each pair of radar give two twin plots which are shifted in time. The cross correlation between the two plots allows the front speed and the variation of the speed along the length of the avalanche to be calculated. When the distribution of the speed is know, the length of the avalanche can be determined. Height of flow, distribution of the mass, shape of the avalanche can be determined too. The FMCW radar explains another important physical phenomena: the erosion and deposition process. Fig. 1 (bottom left) shows the interaction between the original snow cover and the avalanche. Important information such as time, localisation and intensity of erosion can be determined. This information is then analysed in order to formulate mass entrainment theories which are used to implement mass entrainment in numerical simulation codes.