Issue 54: False Color
December 8, 2022
In this week’s issue: We dive into the world of false-color satellite imagery; Hawaii’s Mauna Loa closes out 2022 with a bang; and a highway snakes through mountains in South Korea.
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Feature Story: False Color
No, the images you’re seeing weren’t made by a first-year art student with an old camera and expired film. These are false-color images. Though the name is a bit of a misnomer as these pictures are no more false than bulls’ attraction to red (it’s a myth). It’s just not how we humans perceive the world. False color introduces wavelengths normally unseen by our eyes and uncovers details hidden within landscapes.
There are a few ways of visually representing Earth. Nearly every image we’ve shared in the previous 53 issues has been true color. AKA your typical-looking RGB photo: red is red, green is green, and blue is blue. False color, however, plays a bit of musical chairs with these channels and assigns non-traditional wavelengths to RGB colors. These images introduce at least one wavelength normally invisible to our eyes.
To keep things simple, we’ll be focusing on just one combination: near-infrared, red, and green (NRG). NRG images display near-infrared light in red, red light in green, and green light in blue. This shuffling noticeably changes the look of landscapes in a few ways:
- Vegetation shows up as red. The deeper the shade, the denser and healthier the foliage
- Clear water becomes black
- Cloudy water is seen as a light blue
Many remote sensing experts rush towards these red-laden false-color images like a bull towards a matador. Why? Well as we saw last week, our eyes aren’t always accurate — especially when it comes to viewing satellite data. And since there’s a whole spectrum of light we cannot see, true-color imagery often paints an incomplete picture.
If you noticed there’s about as much red in these images as a Quentin Tarantino film, you’re onto something. Don your middle school science hat for a second and remember how all surfaces reflect unique compositions of light. Plants reflect the green wavelength (hence their Grinchy-greenness) but also near-infrared light (for a deeper dive on colors, read here). So infrared images flip the script and show us plants reflecting infrared in red, instead of green in green.
All that means NRG false-color data is particularly well-suited for representing changes in vegetation. Watch as a forest fire progresses over a 2 month period in Bolivia. As it grows, more healthy forest (bright red) is consumed by fire and turned into burn scar (dark gray and black). The infrared band is less obstructed by smoke as well. It’s about as distinct and direct as a timelapse gets.
Like wildfires, floods also rapidly change vegetation. And the infrared band helps highlight its extent where true color can be a little messy. Consider the two images from recent floods in Australia. It’s harder to parse out the flood water in the true color image on top. But the false color works around the muddling browns and presents a far clearer picture.
We’ve focused here on the visual aspect of false-color imagery — the details revealed by making the invisible spectrum visible. But the real insights come from the underlying data.
The Normalized Difference Vegetation Index (NDVI) and other indices use infrared light to turn images like these into measurements. And we didn’t even get to the applications that come from the other infrared bands (nor the other bands beyond near-infrared). We’ll save those for a future issue. Until then, we hope these false-color images showed you that there’s always more than meets the eye.
Mauna Loa
Hunga Tonga-Hunga Ha’apai started 2022 with a bang and now Mauna Loa is closing it out with one too. For the first time in nearly 40 years the iconic Hawaiian volcano erupted, creating a spectacle for viewers and scientists alike and interrupting atmospheric carbon dioxide measurements at the nearby observation station.
Not all wavelengths of light we capture are reflected from the sun. Some are emitted by the Earth itself. Turn up an electric stove burner to 11 and watch it glow red. The same happens to hot surfaces on Earth. Some things that aren’t quite hot enough to glow visibly to our eyes — which happens when the temperature hits about 600˚C/1100˚F — will emit near-infrared light. So we often use false-color imagery for volcanic eruptions in order to view the glow of lava normally hidden in true color
It’s a bit of a novelty, but who doesn’t like seeing lava? Take a look at the false-color perspective of spewing lava from last year’s Cumbre Vieja eruption and its molten trail towards the ocean.
And check out the true color comparison to see how much of a difference there is between these two image types.
Buried Highway
South Korea’s Donghae Expressway has possibly usurped AC/DC’s Highway to Hell as the most rad mass transit infrastructure. We spotted this highway weaving between and through the country’s coastal mountains (check out the details for the coolest spots). There’s not much else to the image, but we’re working on literally stretching our image capabilities through email. So wind your way with us and remember: it’s not about the destination, it’s about the journey.
