1. School of Civil Engineering and Geosciences; Newcastle University; Newcastle NE1 7RU UK
2. Centre for Earth Systems Engineering Research; Newcastle University; Newcastle NE1 7RU UK
3. Now at Institute of Geography and Earth Sciences; Aberystwyth University; Aberystwyth SY23 3DB UK
4. Earth and Planetary Remote Sensing Laboratory; De Montfort University; Leicester LE1 9BH UK