1. Departments of Geophysics and Electrical Engineering, Stanford University, Stanford, CA 94305, USA.
2. Jet Propulsion Laboratory (JPL), California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
3. Applied Physics Laboratory, Johns Hopkins University, 11100 Johns Hopkins Road, Laurel, MD 20723, USA.
4. U.S. Geological Survey, 2255 North Gemini Drive, Flagstaff, AZ 86001, USA.
5. Departments of Planetary Science and Physics, University of Arizona, Tucson, AZ 85721, USA.