Emerging Tech

What It Looks Like When One Satellite Sees Another

An artist's rendering of a Landsat satellite in orbit around Earth

An artist's rendering of a Landsat satellite in orbit around Earth // NASA/AP File Photo

There will be pictures at the end of this post. I promise. But first, there is a story.

There aren’t many U.S. government programs—even space programs—like Landsat. Since the 1970s, the project’s satellites have continuously imaged the surface of the Earth, providing the longest-running archive of Earth observation photography. You’ve almost certain seen pictures from the Landsat program: They’re used extensively in Google Maps.

It’s very important the government maintains that long-running archive, so there’s usually more than one Landsat satellite in space at any one time. In fact, right now, there are three. There’s Landsat 8, the youngest and spiffiest addition to the program. (It just celebrated its first anniversary of operation, on Tuesday.) Then there’s Landsat 7, which launched in 1999 and still functions despite some technical issues

There’s no Landsat 6. It failed to reach orbit in 1993. :(

There is, however, Landsat 5. Landsat 5 retired only last year after spending 29 operating years in space. It launched in 1984. It was the first satellite to photograph the aftermath of both the Chernobyl accident and the 2004 Indian Ocean tsunami. It is the longest-lasting Earth-observing satellite ever. Landsat 5 is a beast.

It is, however, retired. Last June, after Landsat 8 came online, scientists movedLandsat 5 to a graveyard orbit. It will linger there until 2034, losing and losing altitude until it crashes into Earth’s atmosphere.

So: Three satellites in space. Landsat 5 will orbit for another 20 years. It’s on a graveyard orbit—it’s closer to Earth. Landsat 8 is in an operational orbit. It’s farther from Earth.

Earlier this week, Landsat 8 passed over Landsat 5. The two satellites were much closer to each other than either of them were to Earth, yet—as you’ll see—they’re still a blip against their home planet. But thanks to Mike Gartley, a research scientist at the Rochester Institute of Technology, they’re blips we can see. Here is Landsat 5 as seen by Landsat 8:

USGS

Depending on which color sensor Landsat 8 uses, Landsat 5 appears either white or black. With the “coastal” band, which picks up deep blues, the satellite appears black. It appears the same in the green band:

USGS

In the panchromatic band—which picks up all the colors to form a contrast-heavy black and white image—it appears white:

USGS

Ditto the cirrus band:

USGS

Remember: These are all the same image. They just look different depending on which color that Landsat 8 is sensing. And it’s funny for me to think that a device that looks something like this…

…appears, even to another satellite, nothing more than a visual whoosh.

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