The significance of glaciers is disproportionately greater than their size. Although they contain less than one percent of the total volume of ice on Earth, they are currently believed to be making the major cryospheric contribution to the global rise in sea-level. They are in general more sensitive to variations in climate, and swifter to respond, than the larger ice caps and ice sheets. The evidence that we have suggests that many of the world’s glaciers are indeed responding to a warmer climate, by thinning and retreating. However, in situ measurements are not easy to obtain: most glaciers are located in remote places that are difficult to reach. The desirability of remote sensing methods to study glaciers is clear, and has been recognised for many years.