1. a Remote Sensing Applications Development Unit, British National Space Centre, Royal Aircraft Establishment , Farnborough, Hampshire, GU146TD, England
2. b NERC Computer Services, British Geological Survey , Nicker Hill, Keyworth, Nottingham, NG12 5GG, England
3. c Environmental Information Centre, Institute of Terrestrial Ecology , Monks Wood Experimental Station, Abbots Ripton, Huntingdon, Cambs, PE17 2LS, England
4. d NUTIS, Department of Geography , Reading University , Whiteknights, Reading, Berkshire, RG62AB, England