Ground-penetrating radar for assessing winter roads

Since its inception, ground penetrating radar (GPR) has been a very effective method for examining ice structure. The vast majority of early GPR use was focused on answering questions related to glaciology and ice sheets. More recently, as more and more activity occurs in arctic areas, managing ice structures for a variety of applications has created new uses for GPR. For the past 30-40 years, GPR use for assessing transportation routes over lakes, rivers, and sea ice has been reported, but, only in the last decade has routine application occurred. We have focused on the application of GPR for winter road safety, explained the operational requirements, discussed the current state of practice, and illustrated modern GPR instrumentation. Based on widespread field observations, we have provided information on the ice-layer thickness variation and the variability on GPR ice bottom reflection. Combining extensive GPR and ice auger data provided insight into the variability of electromagnetic wave velocity in ice. Extensive observations showed that velocity varies with ice thickness, and velocities are often considerably lower than observed in "pure" ice.