In sharp contrast to stellar magnetic fields, geomagnetic fields have never been remotely sensed. If geomagnetic fields could be measured remotely at the nanotesla (nT) level or better, our understanding of the processes that produce these fields would advance markedly. Unlike characteristics such as topography and temperature, measurements of the magnetic field are determined almost exclusively in situ. The inability to remotely sense these fields has hindered their utility. The Remote Atmospheric Magnetics Workshop highlighted advances in this frontier area, focusing on lab- and field-based studies.
The conference centered on two main topics: magnetic fields in the mesosphere sensed using sodium (Na) excited with GuideStar technology and magnetic fields in the lower atmosphere sensed by lasers that can be tuned to provide backward lasing or radar signatures.
The mesosphere, the boundary between the atmosphere and ionosphere, is one of the most poorly observed regions in all of space because access is solely by rocket or remote sensing. As discussed by Tom Kane, a proof of concept test for remote sensing in the mesosphere is under development for the Kuiper telescope near Tucson, Ariz. The laser will be pulsed near the Larmor frequency, where measurements of the magnetic field will be attempted using Na in meteoric layers. Magnetic sensitivity goes as 1/[t*root(N )], where N is the number of returned photons detected and t is the coherence lifetime. Models suggest that nT-level measurements may be possible.
In the atmosphere, backward lasing would allow for the efficient sampling of remote regions as the beam returns and has been successfully used on the meter scale in the laboratory with lasers. This same technique might be executed with radar, and Richard Miles presented a thought experiment on how the radar approach, and a variety of pumping concepts, might be used with xenon-129 to achieve resonance behavior that could be interrogated for magnetic intensity.
Many processes in the near-Earth environment produce magnetic fields. The measurement of those fields in frontier regions offers the promise of discovery and further insight into those processes.
The meeting was sponsored by the Office of Naval Research. Selected talks and a list of participants can be found at http://core2.gsfc.nasa.gov/research/purucker/rema.html.
—Michael Purucker, Stinger Ghaffarian Technologies, NASA Goddard Space Flight Center, Greenbelt, Md.; email: [email protected]