File:Mt. Gambier, South Australia.jpg

English: This photo-like image of Mount Gambier was acquired from low-earth orbit by the Landsat 7 satellite’s Enhanced Thematic Mapper Plus (ETM+) instrument. In this late spring image, vivid green fields surround the white limestone and concrete of the town. Much of the greenery is dairy pastureland, supporting one of the major local industries, cheese. Patches of deep, dark green are pine plantations, which support another mainstay of the local economy, timber. But perhaps the most striking feature is the pair of caldera lakes immediately south of the town. True to its name, Blue Lake is blue in the image, even though ETM+ acquired the image a month before the Blue Lake Days festival and the normal colour-turning of the lake. The lake turns blue at different times each year, and the satellite may have captured this image as the lake transitioned from its dark blue winter colour to the bright blue summer colour, a shift that occurs over weeks. Also, the satellite may have observed more blue light than a person standing by the lake would, since blue light tends to scatter up more than out at an angle. Thus someone immediately above the lake looking down would see a more blue-toned surface than a person standing on the rim of the caldera.