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The "dirty" window channel is also sensitive to volcanic ash. Ash particles exhibit a higher emissivity at 12 than at 10.7 microns when compared with water clouds and most surfaces, making the ash plume appear relatively warmer in a 12 micron image. An enhanced detection capability for ash plumes can be produced when the two longwave infrared channels are combined into a derived product image. The product is particularly effective for ash plumes lacking a significant number of water droplets. Notice how well the volcanic ash plume from the Mt. Cleveland, Alaska eruption in February 2001 is isolated from neighboring clouds in the 12 minus 10.7 micron channel brightness temperature difference image on the right when compared to the 10.7 micron image on the left.