1. National Center for Earth and Space Science Education, Capitol Heights, Maryland.
2. NASA/Goddard Space Flight Center, Greenbelt, Maryland.
3. Current address: University of Maryland, College Park, Maryland.
4. University of Maryland, College Park, Maryland.
5. Harvard University, Cambridge, Massachusetts.
6. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland.
7. University of Washington, Seattle, Washington.
8. Massachusetts Institute of Technology, Cambridge, Massachusetts.