The loss of Landsat 6, at launch, and the ageing sensors on board Land
sats 4 and 5, enhance the value of existing TM images. This letter sho
ws that 88 per cent of Britain was imaged as cloud-free scenes or quar
ter scenes, in both the summer and winter of 1988-1990 and 97.5 per ce
nt was imaged on at least one date. Acquisitions in 1991-1993 have bee
n few.