Martian clouds in motion

Posted By Emily Lakdawalla

2011/08/19 10:36 CDT

Topics: pretty pictures, podcasts and videos, Mars Express, Mars, atmospheres

Behold an amazing (if I do say so myself) video of Martian clouds in motion.

ESA / DLR / FU Berlin (G Neukum); animation by Emily Lakdawalla

The images that compose this animation were taken on October 14, 2010, on Mars Express' 8676th orbit, and show an area within Noachis Terra to the west of Hellas basin, around 45 degrees south, 38 east. There are two components to the apparent motions of the clouds. One is real west-to-east cloud motion over the two-minute period of the animation (readable from the motions of the shadows along the ground). The other component has to do with the different look angles of the different channels of HRSC and the significant thickness of the cloud layer. In the first frame, HRSC was looking forward (northward) along its south-to-north orbital path; in the last frame, it was looking backward (southward). Because of this changing perspective, the upper-level clouds appear to move southward with respect to the lower-level clouds.

The color comes from red, green, and blue channels of the HRSC channel and is an overlay applied to the animation, so the color information is actually not animated -- only the brightness information moves. This works visually because Mars is relatively monochromatic.

This video represents a milestone for me -- I learned how to "tween" an animation! "Tweening" is short for "inbetweening," a word coined by animators to describe the generation of frames in between two key frames. Back in the day, when animations were hand-drawn, the senior animators would draw key moments in character action in a cartoon, and their lackeys would tween them, creating frames that filled in the time between the two key points. The need is similar with animating space images, because individual photos from space are almost never taken at a high enough frame rate to appear to animate smoothly.

Making these few seconds of video was a somewhat arduous process, but I think the result was worth it. The process can be broken down into two big tasks: generating the individual animation frames from the raw data, and generating a tweened animation from individual animation frames. The first task I already knew how to do (though there were some wrinkles with dealing with Mars Express HRSC data). I am exceedingly grateful to Ian Regan for patiently explaining to me via email how to do the second task. And also to Marc Canale who first pointed out the moving-cloud images in the latest release of HRSC data by posting his own animation on unmannedspaceflight.com.

I'm almost done writing a "how-to" explainer for making this movie, but it's quite long, so I'm going to post it separately, in two parts, next week. So stay tuned!

EDIT: Part 1 of the how-to explainer is now available.