1. Carnegie Institution of Washington, Geophysical Laboratory, 5251 Broad Branch Road N.W., Washington, DC 20015, USA.
2. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, CA 91109, USA.
3. Witec GmbH, Lise-Meitner-Straße 6, D-89081 Ulm, Germany.
4. Department of Geosciences, Stony Brook University, Stony Brook, NY 11794–2100, USA.