From: NASA MODIS Web
Posted: Tuesday, February 26, 2013
On February 16, 2013 the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite flew over the actively erupting Plosky Tolbachik volcano and captured this set of images of a large plume of steam, gas and ash rising from the caldera. The top image is a false-color image, created from data taken from the 3, 6 and 7 bands on the MODIS instrument. This color combination allows easy visualization of the broad plume blowing to the northwest of the caldera, despite the surrounding sea of clouds and background of snow. The clouds and snow appear orange, while the volcanic plume appears a dull white. Scrolling over the top image brings the true-color version of the same image into view. Here the snow on the ground can be seen as a bright white, while the veil of clouds overlying the land is less intensely white. The blowing plume appears very similar to several thicker clouds nearby, as well as the snow. With this image alone, it would be difficult to discern the volcanic plume. By combining various MODIS bands, each of which collects a different frequency of light, scientists can enhance features that might otherwise be overlooked in true-color imagery.
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