NASA MODIS Image of the Day: May 9, 2012 – Plume from Zavodovski volcano, South Sandwich Islands (false color)
On a cloudy and windy spring day, NASA’s Aqua satellite passed over the South Sandwich Islands just as a plume was rising from an active volcanic eruption on Zavodoski Island. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard that satellite acquired data of the event as it occurred on April 27, 2012 at 16:20 UTC (2:20 p.m. local time). From that data this set of images was created. The top image is a “false color” image. It uses a combination of non-visible (middle infrared and infrared) and visible (red) light captured in bands 7, 2, and 1, respectively, to distinguish clouds from snow and ice. Here the ice-covered islands appear bright turquoise, the clouds light turquoise and the water in the ocean appears deep black. Because the volcanic plume is a moist mixture of gas and ash, it reflects all three forms of light relatively well, so it appears nearly white, and clearly stands out as different from anything else in the image. Rolling over the top image will reveal a “true-color” image. This is created by using visible light (red, green and blue) which are captured by bands 1, 4 and 3, respectively by the MODIS instrument. These are the same colors used by the human eye so, when combined, the resulting image looks very much like what would be seen if a person could watch the event themselves. Compared to the enhanced, false-color image, the true-color is not only less vibrant, but the clouds, ice and volcanic plume all appear very similar. Each appears white, with the dark ocean as a backdrop. The cloud vortices on the leeward side of the island, formed by the motion of the wind blowing around the immobile land, appear similar to the volcanic plume. The similar color and curling patterns could lead one to wonder if at least some of the vortices could also be smaller volcanic plumes. While the human eye, and true-color images, are very strong and reliable tools, there are times when enhanced imagery can aid understanding. The MODIS instrument captures data in 36 separate bands, giving tremendous power to study the Earth’s atmosphere, ocean and land.
