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Less than one percent of the United States is mapped by aeromagnetic data that fully meet modern standards and best practices, according to a recent evaluation by the U.S. Geological Survey. Less than five percent of the country has been mapped with data that can be considered adequate in meeting those same standards

Aeromagnetic surveys measure the intensity of Earth’s natural magnetic field. Because different types of rock formations can alter the readings of the magnetic field, variations in the data can allow scientists to create two- and three-dimensional models of the geology of Earth’s crust.

High-quality aeromagnetic data can help geologists characterize features on the surface and below, providing information directly relevant to geologic mapping and structure, mineral resources, groundwater, earthquake hazards, volcanic hazards, and petroleum resources. Moreover, aeromagnetic data are inexpensive to acquire compared with other types of geoscientific data.

Image shows a map of the United States with varying coverage of aeromagnetic surveys
Assessment of the quality of existing aeromagnetic surveys for the United States, with rank 1 indicating the best quality and rank 5 indicating the worst. The map results from the ranking scheme applied to each public aeromagnetic survey by Eric Anderson, Ben Drenth, V. J. S. Grauch, Anne McCafferty, Anji Shah, and Dan Scheirer of the USGS.

Currently, although most of the United States has been mapped with aeromagnetic data, much of it is old or out-of-date. To help evaluate where modern aeromagnetic surveys are required, the USGS examined all of the publicly available survey datasets and ranked them from 1 to 5, with rank 1 being data that fully meet modern standards and are appropriate to support the widest possible variety of geoscience studies.  

Only one percent of the United States has been mapped with rank 1 data, and none of Alaska or Hawaii have been mapped with rank 1 data. Instead, more than 95 percent of the country is covered by ranks 3, 4, and 5 data.

Image shows a helicopter resting on the prairie with mountains in the background
Coauthor Tien Grauch (middle) with the flight crew as they prepare to survey the magnetic field near Great Sand Dunes National Park and Preserve in Colorado.

Future improvements in aeromagnetic surveys will help not only geoscience efforts throughout the country, but also efforts to improve the Nation’s understanding of its domestic critical mineral resources.

Compiling geoscience data like these surveys is one way that the USGS is meeting its obligations in the 2019 Federal Strategy to Ensure a Reliable Supply of Critical Minerals, which directs the U.S. Department of the Interior to improve mineral information, resource assessments, and mapping/geophysical surveys to identify domestic critical mineral resources. As part of that strategy, the USGS has embarked on a new nationwide program of surface and subsurface mapping–the Earth Mapping Resources Initiative–to better inform the country about its critical minerals potential.

Image shows an illustration of the large improvement in resolution of rank 1 over rank 4 data.
Comparison of rank 1 and rank 4 aeromagnetic surveys for geologic mapping of the Albuquerque Basin near Albuquerque, N.M. In this area, the shallowest magnetic sources (magnetic sediments and volcanic rocks) are at the ground surface, so the shallowest source depth is the same as the terrain clearance. The rank 4 survey is from a 1974 digitized contour map with line spacing of 1,609 meters (m) and average terrain clearance of 621 m (ratio of 2.6). The rank 1 survey is from 1996–1997 data, taken with real-time GPS navigation. Line spacing and terrain clearance are 100–150 m (ratio of 1.0). Color scale is magnetic field strength in nanoteslas. QT is Quaternary-Tertiary; s is alluvium and basin-fill sediments; v is intrabasin volcanic rocks; Mz is Mesozoic sedimentary rocks on the basin flanks; thick black lines represent major basin faults. See Grauch and Hudson [2007] for more details.

The USGS Mineral Resources Program delivers unbiased science and information to increase understanding of ore formation, undiscovered mineral resource potential, production, consumption, and how minerals interact with the environment.  USGS supports data collection and research on a wide variety of non-fuel mineral resources that are important to the Nation’s economic and national security.