1. Colorado Center for Astrodynamics Research, University of Colorado Boulder, 3775 Discovery Drive, 429 UCB, Boulder, CO 80303, USA
2. NOAA Physical Science Laboratory, R/PSD2 325 Broadway, Boulder, CO 80305, USA
3. Research and Development Department, Norwegian Meteorological Institute, 0313 Oslo, Norway
4. Applied Physics Laboratory, Polar Science Center, University of Washington, Seattle, WA 98105, USA
5. DTU-Space, Technical University of Denmark, DK-2800 Lyngby, Denmark