LOW FREQUENCY (50, 100, 200 MHZ) GROUND PENETRATING RADAR ANALYSIS OF THE NIPISSING BEACH RIDGE, HURON MOUNTAINS, MI

Lake Superior has undergone a number of lake level phases that have resulted in the formation of beach ridges. One beach ridge that corresponds with the Nipissing phase of Lake Superior is located 0.5 km inland from the present southern Lake Superior shore within the Huron Mountains, MI. Two parallel, low frequency ground penetrating radar (GPR) transects were collected over the ridge to better understand the subsurface stratigraphy. The transects were collected using a pulseEKKO 100 GPR system with 50, 100, and 200 MHz antennae, 1000V transmitter, varying antennae separation and step size. The first transect was 100 m long while the second transect (30 m to the east) was 65 meters long. A common midpoint survey was used to calculate the near surface velocity of the sediment. Topographic data was collected using a Topcon RL-H3CL laser level to geometrically correct the profile for changes. The low frequency antennae allow for greater depth of penetration and can highlight dominate bedding patterns. Depths of penetration ranges from > 30 m for 50 MHz antennae to > 10 m for the 200 MHz. Preliminary results indicate that lakeward dipping reflections on top of horizontal to subhorizontal reflection patterns which indicate an aggradational and progradational coastal environment.