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By Emily Lakdawalla

Pretty Picture: ISS in the X-band

Mar. 4, 2010 | 07:40 PST | 15:40 UTC

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This is from the "Just Plain Cool" department: a picture of the International Space Station taken in microwave radar. The specific radio wavelength involved is the X-band, radio with wavelengths of a few centimeters. (I've noticed some bloggers incorrectly reporting this image as being taken in "X-rays," which is quite a different animal entirely, waaaaay shorter wavelength than visible light and not a very friendly wavelength to be irradiating astronauts with; microwave radar is waaaay longer wavelength than visible light and of no consequence to astronaut health.) For comparison, I'm also posting an image of the ISS taken with a plain old optical camera just a couple of months later.

Click to enlarge >

ISS in the X-band
On March 13, 2008, the International Space Station (ISS) passed across the field of view of Germany's remote sensing satellite, TerraSAR-X, at a distance of 195 kilometers.

In contrast to optical cameras, radar does not "see" surfaces. Instead, it is much more sensitive to the edges and corners which bounce back the microwave signal it transmits. Unless they are directly facing the radar spacecraft, smooth surfaces such as those on the ISS solar and radiator panels, do not reflect a strong signal to the detector, so they appear dark. Yet the bright spots outlining edges and corners clearly show the shape of the ISS. The central element on the ISS, to which all the modules are docked, has a grid structure that presents a multiplicity of reflecting surfaces to the radar beam, making it readily identifiable. This image has a resolution of about one meter.

Credit: German Aerospace Center (DLR)

Click to enlarge >

The International Space Station, June 11, 2008
As the Space Shuttle Discovery departed the International Space Station, the astronauts photographed their handiwork, which included the addition of the Japanese "Kibo" experiment module, a tube-shaped element at the top left of the Station in this image. Earlier in the year, Atlantis carried the European Space Agency's Columbus module into orbit. The two modules vastly increase the scientific capability of the station, fulfill important international obligations, and bring the Station to a state of near completion. After October's Hubble Servicing Mission, nine Shuttle launches remain, with most of the remaining large Station components (including the final set of solar arrays and an Italian habitation module that can double the crew from three to six) scheduled for launch in 2009. Credit: NASA

The main reason I'm posting this picture is because it's a picture of a pretty familiar object -- the Space Station -- in an unfamiliar part of the electromagnetic spectrum. I post images here all the time in wavelengths longer than the human eye can see, and it's tempting to assume that images of the same places will look pretty much the same in visible wavelengths. But the photo above shows how simultaneously familiar and strange a well-known object looks in radar, reminding me that my instincts in interpreting what I see in radar images of places like Titan, Venus, and the Moon may not always be reliable.

A final note about this image -- I first learned about it via DLR's Twitter feed. I'm finding it easier to get news about European missions via Twitter than more traditional means!

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This is how Predator sees the ISS...

#1 - J. Major - 03/04/2010 - 14:51

I've used some Space Shuttle gathered SAR data to check "ground truth" that is, published elevations and contours (USGS) once for an archaeology survey in North Creek, in New York's Adirondacks. It's where US amateur skiing's thought tookoff, at the then railhead (and today) that VP Teddy Roosevelt, after a series of buckboard rides down from Tahawas at night, had read a telegram that President McKinley had died from the gunshot in Buffalo, NY and he was US President. Titanium oxide was mined there in WWII and the Cold War, near the old iron mines.

#2 - George Myers - 03/10/2010 - 10:23

I find it interesting that in this long wavelength, the fine structure between the solar panels is fairly pronounced, in spite of it being difficult to see in visible wavelengths. I suppose that's because there are so changes in slope in the lattice.

#3 - Worlebird - 03/19/2010 - 14:21

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