1. NWO-I/SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
2. NWO-I/SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
3. Optics Group, Department of Imaging Physics, Delft University of Technology, Delft 2628 CJ, The Netherlands