1. Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire 03755, USA
2. Physical Science Department, Embry-Riddle Aeronautical University, Daytona Beach, Florida 32114, USA
3. NASA Jet Propulsion Laboratory, Pasadena, California 91109, USA
4. Earth and Atmospheric Sciences, Cornell University, Ithaca, New York 14853, USA
5. Department of Physics, University of New Hampshire, Durham, New Hampshire 03824, USA
6. SRI International, Menlo Park, California 94025, USA