A National High-Altitude Magnetic Survey

**Statement of Problem**. Understanding the magnetic properties of the
earth's crust at continent-wide scales provides tectonic, geothermal,
and geodynamic insights important to a variety of USGS missions.
Although the United States already has a continent-wide aeromagnetic
database, it was created by merging hundreds of aeromagnetic surveys of
highly diverse quality and technical specifications. Although useful for
many applications, the patchwork nature of the U.S. compilation includes
long-wavelength errors that hinder many kinds of continent-scale
interpretations.

**Objectives**. The USGS is currently working with the National
Aeronautics and Space Administration (NASA) and other organizations to
develop plans for obtaining high-resolution topographic data for the
entire United States. One option under discussion, advocated by NASA,
calls for flying lidar equipment at 12-km altitude along closely spaced
parallel flight lines. The specifications for this lidar survey turn out
to be ideal for a high-altitude aeromagnetic survey as well. If the
lidar survey should go forward, the U.S. Geological Survey should
support and promote the inclusion of a vector magnetometer, as well as
support and promote the processing and interpretation of these new
high-altitude aeromagnetic data.

**Strategy**. The USGS is uniquely positioned to take advantage of this
"ship of opportunity". The lidar mission is only in the planning stages
now, but USGS scientists are actively working with NASA scientists to
include a vector magnetometer on the survey platform. The program will
take years to complete, but the resulting aeromagnetic data will provide
critical information regarding the nature of the earth's crust for years
to come.

**Relevance and Impact**. Today's National aeromagnetic database was
derived from a patchwork of hundreds of low-altitude surveys of highly
variable quality and technical specifications. While certainly the best
compilation possible with available data, it suffers from the lack of a
regional framework in which to hang the individual surveys. To stitch
diverse datasets into a consistent coverage requires a continent-wide
survey flown as a single mission. A properly merged aeromagnetic
database is critically needed in many areas of USGS research, but in
addition, the high-altitude survey would stand alone as a powerful
research tool, providing critical information for crustal scale
investigations. Foremost among these is the production of a National map
of Curie-temperature depth, the depth at which rocks become too hot
(\>580°C) to support spontaneous magnetization. This very difficult
calculation suffers from long-wavelength errors so prevalent in current
aeromagnetic compilations. A consistent high-altitude survey would
provide, for the first time, the data needed. Understanding spatial
variations in Curie-temperature depth would provide insights into a
variety of areas important to USGS missions, including geothermal
resource evaluation, mineral resource assessment, volcano and earthquake
hazard research, and models of geodynamic processes.

**Partnerships**. The U.S. Geological Survey would work closely with
NASA and various universities in acquiring these data. Products
resulting from this project would have value to many of USGS
stakeholders.