Near the equator, there is a rhythmic wave structure in a cloud belt. Near the north pole, the mottled texture of high clouds is juxtaposed with atmospheric holes that look similar to IR views of Saturn’s pole. Several image processing techniques were required to tease out these details, which are usually very subtle but coherent. It’s common in astronomy to take large numbers of images at a rapid rate, and then stack them up in order to bring out details. This stacking involves carefully aligning the images, and then averaging them. This helps reduce the effects of random noise and sharpens them. Since Uranus rotates fairly rapidly, the astronomers had to “reproject” the images onto flat maps, and then convert each image from an orthographic to a cylindrical map projection. The images were then shifted to compensate for Uranus’ rotation. Uranus’ surface is a hydrodynamically circulating atmosphere, which has winds that move at different rates at different latitudes, so the astronomers had to further shift the images. After this elaborate process, the images were stacked. Most of the variation in pixel values in their stacked composite was from broad-scale atmospheric banding. They applied a high-pass filter to remove the broad features, leaving only smaller, more local features.
