Multi-offset ground penetrating radar data for improved imaging in areas of lateral complexity — Application at a Native American site

Abstract

Multi-offset ground penetrating radar (GPR) data offers numerous imaging benefits over common offset GPR data, such as increased signal to noise ratio and depth penetration, and improved reflector continuity and dip imaging. Another relevant benefit of multi-offset data is the improved lateral imaging capabilities it provides. Neglecting lateral complexity considerations can produce an erroneous interpretation. An example from a Native American archaeological site highlights how 200 MHz multi-offset data provides a better estimate of the lateral density of possible archaeological material, as well as more accurate depth estimates. This is compared to 200 MHz common offset data, which produced an erroneous interpretation both in terms of potential archaeological material density and depth. This analysis also highlights an important caveat of multi-offset acquisition, which is having suitable near-surface conditions to realize improved data quality. Common offset reflectivity is very sensitive to changes in water saturation, and multi-offset data even more so due to the additional dependence of reflectivity on the multiple angles of investigation. A multi-offset section at the same location, but acquired under drier conditions, produced little imaging improvement over the common offset section. Even given the imaging benefits of multi-offset data, it is seldom acquired mainly due to the tedious task of single channel acquisition with bistatic GPR systems. Acquiring the multi-offset traces continuously as common source gathers while still maintaining positioning accuracy and signal quality halved the acquisition time of this multi-offset dataset.