Dielectric properties of thawed active layers overlying permafrost using radar at VHF


  • Steven A. Arcone,

  • Allan J. Delaney


Field measurements of the dielectric constant of thawed active layers of up to 1 m in depth at four sites in Alaska have been made using short-pulse ground radar whose returns were received in the near-field radiation zone. Three sites consisted of saturated silts with varying amounts of organic material, and the fourth site was a moist sand. The reflector returning the radar signals was the active layer/permafrost interface. Analysis of the waveforms showed that all the materials were nondispersive over the radar pulse bandwidth (75–225 MHz), and this was confirmed by time domain reflectometry (TDR) studies of field samples. The average dielectric constants were between 23 and 34 for the silts, which averaged between 45 and 50% water by volume, while the sandy site gave an average value of about 12 for a probable water content of about 23% by volume. These values are very similar to the laboratory work of others and were also confirmed by TDR. The high dielectric constants of the saturated materials allowed accurate profiling of active layer depth, and an example is presented. More detail would probably be achieved with a higher-frequency radar.