GROUND-PENETRATING RADAR REFLECTION PROFILING OF GROUNDWATER AND BEDROCK IN AN AREA OF DISCONTINUOUS PERMAFROST

We have used ground-penetrating radar to profile the depth to permafro st, to groundwater beneath permafrost, and to bedrock within permafros t in alluvial sediments of interior Alaska. We used well log data to a id the interpretations and to calculate dielectric permittivities for frozen and unfrozen materials. Interfaces between unfrozen and frozen sediments above permafrost were best resolved with wavelet bandwidths centered at and above 100 MHz. The resolution also required considerat ion of antenna configuration? season. and surface conditions. Depths t o subpermafrost groundwater were profiled where it was in continuous c ontact with the bottom of the permafrost, except near transitions to u nfrozen zones, where the contact appeared to dip steeply. The complexi ty of the responses to intrapermafrost bedrock, detected at a maximum depth of 47 m, appears to distinguish the se eve nts from those of sub permafrost saturated sediments. The relative dielectric permittivity r anged between 4.4 and 8.3 for the permafrost, and between 12 and 45 fo r partially to fully saturated, unfrozen silts and sands. Scattering l osses are evident from intrapermafrost diffractions and from the impro ved penetration achieved by lowering the midband radar frequency from 100 to 50 MHz.