1. Department of Electronics and Nanoengineering Aalto University Tietotie 3 Espoo FI‐02150 Finland
2. Centre for Electronic Imaging The Open University Walton Hall Milton Keynes MK7 6AA UK
3. Teledyne e2v 106 Waterhouse Lane Chelmsford Essex CM1 2QU UK
4. ESA‐ESTEC P.O. Box 299 Noordwijk 2200 AG The Netherlands