Revealing stratigraphy in ground-penetrating radar data using domain filtering

A common-offset ground-penetrating radar profile was collected from a mid-continent fluvial environment characterized by sand with discontinuous clay layers. Signal was separated from coherent noise by a domain filter that exploits local differences in dip between signal and noise. This filter proved effective in separating reflections from the direct air wave and from system ringing. The processed section locates the base of a Pleistocene river channel incised into bedrock and shows a change in a recent position of the river on the basis of radar character. The water table, which lies at a depth of approximately 2 m, is characterized by a continuous reflection. An earlier reflection is interpreted as a perched lens of water near the ground surface. The predominant frequency of both reflections varies greatly with position along the profile. Shallow cores taken along the profile provide evidence that grain size in the transition zone from saturated to unsaturated sediments may determine the predominant frequency of the associated radar reflection. The domain filter is also successful in separating transition zone reflections from saturated layer boundary reflections that are coincident in arrival time. It is possible, therefore, to determine both grain size in the transition zone and the dip of sediments immediately beneath it even if the reflections from the two are superimposed.