Determination of Lunar Regolith Thickness and Exploration for Frozen Lunar Water Using Human-operated Ground-penetrating Radar

Introduction: The thickness of the lunar regolith and potential for frozen water are important considerations for future lunar outposts. However, the thickness of the regolith is largely unknown and the presence of water ice has yet to be directly detected at or beneath the surface. A rapid and economical geophysical method to determine both the thickness of the lunar regolith and possibly identify the presence of water ice is surface ground-penetrating radar (GPR). Although GPR methods have been proposed for future missions, they rely on lower-resolution orbiting platforms or unmanned rovers. We believe that astronaut-operated surface GPR experiments during the early lunar sortie missions are superior to unmanned experiments because of the high resolution available with surface experiments, ability to collect common midpoint (CMP) velocity soundings, rapidity of acquisition, longer profiles collected at a variety of target depths, flexibility of operation, and ability to take advantage of unplanned scientific opportunities. The astronauts would collect profile GPR data from their rover or by hand as they move between other experiments. They would subsequently collect CMP velocity soundings with two movable antennas over several good data return areas, or interesting anamolous zones, for subsequent depth conversion of the profile data. GPR Method: The GPR method consists of sending an electromagnetic radar pulse in the megahertz to gigahertz frequency range down into the ground. A single trace (or a series of traces from the same location that are added or “stacked” together) is then recorded for a certain length of time, with reflections appearing as the pulse echos off the boundaries between sediment or rock units below (Figure 1).