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Emily LakdawallaDecember 6, 2007

More on the Chang'e image flap

So the story that I wrote about the Chang'e image not being fake but also containing a small processing error has been propagating across the Internet -- it showed up in Alan Boyle's Cosmic Log on MSNBC, on John Borland's Wired Science blog, and on New Scientist's blog, among many other places. These other blogs have all treated the story pretty evenhandedly, but I've been dismayed by the color of the commentary in the replies by readers of these blogs; so many people are unwilling to drop the idea that the images were somehow faked, with the obvious subtext being that those Chinese can't be trusted. I agree with John Borland, who commented:

It's odd that moon images are so often questioned. We can do so many other things that stagger the imagination; why are people reluctant to believe that we can't go to the Moon? I find it also particularly interesting that many people are apparently willing to believe something so improbable (faking a moon mission? That's serious business, way harder than faking a memoir or a resume).

Skepticism is certainly useful, but there's an ugly scent in the air when so much extraordinarily bitter criticism gets leveled at China in particular.

Let me state clearly that I congratulate the Chinese for their achievement of departing Earth for the first time, and placing a spacecraft into lunar orbit, a spacecraft that has already proven capable of delivering beautiful images that will improve on the global Clementine image map. Let me further state that the minor mistake made by the chief scientist in pointing to one crater as a new crater was just that, a minor mistake, caused by an inadvertent error in routine image processing. I extend my congratulations to the Chang'e science team, headed by Ouyang Ziyuan, and would also like to express chagrin that what should be a celebratory time for them is being overshadowed by this silly conspiracy theory.

Some may call me too much of an optimist, but I'll tell you a story. When I was in graduate school at Brown University, I was privileged to have daily interactions with several Russian planetary scientists, including Sasha Basilevsky, Misha Ivanov, and Misha Kreslavsky. This was well after the Soviet Union fell so it wasn't that unusual for Russian and American scientists to be working together. But the working relationships between these scientists and my advisor, Jim Head, had been formed years earlier when the level of distrust between the Soviet Union and the United States was higher than the level of distrust is between the United States and China is now. Somehow, Jim and Sasha and many other participants managed to forge close working relationships including the exchange of data, even convening meetings taking place in Providence and Moscow every year from 1985 on, to facilitate cooperation and exchange among scientists from both sides of the Iron Curtain.

It is possible, even in extremely tense diplomatic circumstances, for science to unite us. I won't deny that there is nationalism behind space missions -- if there weren't any nationalistic goals, governments probably wouldn't pay the bills -- but even if the program itself is intensely nationalistic, the science that happens as a result of the space program is usually much less so. There is so much international exchange among scientists, beginning when graduate students acquire their educations in countries other than their native ones, that space science tends to break down barriers among countries. At its heart, science is a quest for truth and clarity; to be accused of falsifying data is probably the worst thing that can happen to a scientist (professionally speaking), and I don't believe that Chinese scientists are any different from any other scientists in this regard. How distressing it must be for the Chang'e team to be so accused! I am happy to say that the comments I've received directly from you, dear readers, have not shown this kind of prejudice.

I'll repost again the pretty picture in question:

Chang'e 1's first picture of the Moon (with scale bar)


Chang'e 1's first picture of the Moon (with scale bar)
This image is the first returned from the Moon by Chang'e 1, China's first spacecraft beyond Earth orbit. The 19 separate images that compose this view were captured over two days, November 20 and 21. Each image was 60 kilometers wide; the entire image is about 460 kilometers long and 280 kilometers wide, located within a box from 54 to 70 degrees south latitude and 57 to 83 degrees east longitude. It includes mostly areas of highlands but contains some of the dark basalt plains of Mare Australe at the upper right. The scale bar at lower right is 50 kilometers long. The 66-kilometer-diameter crater Gill is just to the lower right of center in this image. Cut off at the upper left side is 91-kilometer Pontecoulant. At the bottom edge is 94-kilometer Helmholtz.
A couple of Chinese readers have emailed me with very helpful pointers to further information on Chinese-language websites. One very interesting website is this one, a space-related discussion forum, on which the mystery of the new crater was discussed and solved a day before I figured it out. Google translator won't work through the whole page (you have to plug the text one line at a time into the Google tool instead), but if you just look at the images you can see how their argument developed. This image points out a number of other features that were similarly displaced across the image seam. Clearly this was an inadvertent error.
Seam in the Chang'e mosaic

CAST / "Mei de Yan Jing"

Seam in the Chang'e mosaic
An individual posting on a Chinese language space discussion forum located several features in the first image from Chang'e 1 that are offset across an image seam. He found that there appeared to be a displacement of about 3 kilometers along a few-hundred-kilometer stretch of the image seam, and that it seems to be no more than an inadvertent mistake.
Another commenter pointed me to this website, which contains what appear to be Powerpoint slides from a presentation on the first data back from Chang'e 1, including several 3D views; the camera that produced that first image is, in fact, acquiring a stereo map of the entire Moon. These 3D views are really promising. However, they are pretty low resolution; I hope the mission posts these for public consumption at higher resolution sometime.
3D view of Chang'e 1's first image


3D view of Chang'e 1's first image
Chang'e's camera simultaneously shoots three images along the spacecraft's track. The multiple look angles allow the calculation of digital elevation models of the lunar terrain. This is a perspective view of the first image released by the Chang'e 1 mission.
The same fellow on the Chinese-language forum who pointed out the displacements above also noticed that, in this perspective view, the misalignment of the crater that chief scientist Ouyang originally pointed out as being a new crater has been fixed!
3D view of Chang'e 1's first image (crater highlighted)

CAST / "Mei de Yan Jing"

3D view of Chang'e 1's first image (crater highlighted)
In this perspective view, a crater that was misaligned in the first image release from Chang'e 1 has been restored to its correct shape.
Finally, a very helpful reader pointed me to a detailed essay written by Ouyang Ziyuan himself on how the first image was captured, transmitted to Earth, and processed before its release, perhaps in order to counter the silly accusation that they faked it. The essay is in two parts, here and here; and here and here are links directly to the Google translations, if you feel like wading through them. Here's what I consider the most interesting image from that article, showing the ground tracks of the 19 image strips from which they assembled the image. They overlap a lot at this high southern latitude. The mostly intelligible Google translation talks about the preliminary nature of their location mapping of the image swaths: "...coordinates for the calculation is based on rough ephemeris and data on crude gesture, a certain degree of accuracy error; follow-up treatment will be used after the precise ephemeris data and inertial fine gesture, a certain accuracy will be improved." Which is basically what I said in my previous post -- over time, they'll improve their tracking information of their spacecraft, and that will yield more accurate location information for their image ground tracks, which will, in turn, yield better-quality mosaics.
Ground tracks of the image strips in the first Chang'e 1 image


Ground tracks of the image strips in the first Chang'e 1 image
This map shows the ground tracks of the 19 image strips used to construct the first Chang'e 1 image. The easternmost, pink tracks are from November 20; dark green are from November 21; and light green are from November 22. The cross-hatched area at the right side of the image shows the 60-kilometer swath width of a single image; at this high southern latitude, the image swaths overlap significantly.
Thanks to all the readers who commented on the original story, and especially to those of you who can also read Chinese language websites and have sent me such useful links.

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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