Starting this June, a helicopter towing a large hula hoop-shaped sensor will fly just 100 to 200 feet above the forests, coastlines, and waters of the Lake Superior Basin. The flights span Michigan, Wisconsin, and Minnesota — and they’re designed to see far deeper than the treetops below.
This is a USGS-led geophysical survey capable of imaging geology up to 1,500 feet underground. The target region holds roughly 10% of Earth’s surface freshwater and sits atop mineral deposits that federal officials consider essential to U.S. national security. What lies beneath is only beginning to come into focus.
A sensor shaped like a hula hoop — and what it can see underground
The hula hoop comparison isn’t just colorful — it’s accurate. A large hoop-shaped sensor towed beneath the helicopter measures tiny electromagnetic signals as it passes over the landscape, revealing changes in the electrical conductivity of rocks below the surface. Those changes expose the structure of buried geology that would otherwise remain invisible.
The resulting data gets processed into high-resolution 3D models stretching from the surface down to roughly 1,500 feet — about 500 meters. Deep enough to trace groundwater pathways, identify mineral deposits, and map geological formations no drill has ever touched.
One common concern with low-flying aircraft: safety. USGS is direct on this point. None of the instruments pose any health risk to people, animals, or plant life, and no photography or video is collected during the flights.
Why Lake Superior sits at the center of a national mapping push
The Lake Superior Basin is the largest freshwater resource in the United States, holding roughly 10% of all surface freshwater on Earth — a figure that puts its global significance into sharp relief. Two groundwater-focused projects supported by these flights will work specifically to characterize and protect that resource. Understanding where water moves underground — through what rock, at what depth — is essential for managing it wisely.
The basin’s geology also tells a much older story. The rocks here record continental history spanning more than one billion years. Michigan, Minnesota, and Wisconsin aren’t just funding partners; their state geological surveys are co-leading the effort alongside USGS, bringing deep regional expertise to a nationally significant project.
Critical minerals beneath the surface — and why graphite matters most
The Lake Superior region has a long history as one of the most productive mining areas in North America. This survey aims to build on that legacy with far more precise subsurface knowledge.
Graphite sits at the top of the target list. It appears on the USGS List of Critical Minerals — materials deemed essential for the U.S. economy and national security — and is used in batteries, steelmaking, and defense applications. The strategic problem is stark: the United States currently imports 100% of its graphite, primarily from China. Better subsurface maps of the Lake Superior Basin could help identify domestic sources and reduce that dependence, without a single additional drill hole. At least not yet.
From June through fall: how the survey will actually unfold
Flights begin in June and continue into fall, weather and FAA restrictions permitting. The helicopter follows pre-planned paths at 100 to 200 feet above the ground — low enough to collect detailed data, high enough to clear most terrain features. That kind of flying requires specialized skills, so the aircraft will be piloted by aviators specifically trained and approved for low-level operations, with the survey contractor coordinating with the FAA throughout.
All surveys happen during daylight only. Helicopters won’t fly directly over buildings at low altitude, and densely populated areas are excluded from low-level passes. Flight bases will shift between airports across the three states as needed, reducing travel distances and working around weather. USGS has contracted NV5 and SkyTEM Surveys to carry out the data collection.
Part of a broader effort to modernize America’s geologic knowledge
This survey isn’t a standalone project. It’s part of the USGS Earth Mapping Resources Initiative — Earth MRI — a national program now active across 45 states to update the country’s geologic and mineral resource maps.
Earth MRI draws on multiple methods: airborne electromagnetic surveys like this one, LiDAR topographic mapping, geochemical reconnaissance, hyperspectral surveys, and traditional geologic mapping. Together they build a far more complete picture of what lies beneath American soil. All data collected over Lake Superior will be made freely available through the USGS ScienceBase website, meaning researchers, planners, and state agencies can use the results for land-use decisions, infrastructure planning, and groundwater protection near legacy mining areas.
The flights this summer are just the data-collection phase. Processing, modeling, and analysis will follow. What those 3D maps ultimately reveal about the basin’s mineral potential and hidden water systems could shape decisions across the region for decades to come.