Smoke plume summer: Watching wildfires from space with Landsat 8 and Google Earth Engine
Updated: Jan 6, 2021
We marked the passage of the long, hot late summer days in Steamboat Springs by watching smoke plumes billowing on the eastern horizon. The Middle Fork Fire - in the Mad Creek drainage of the Zirkel Wilderness Area - was the closest, shrouding the Yampa Valley in smoke, humming in the background of the collective consciousness for months. But we only saw one dimension from town: the towering smoke columns that never seemed to change when you stared at them, but morphed and billowed if you blinked too long. What could we see if we could sail 438 miles over Earth? Enter Landsat: a satellite program that's been doing just that for more than 40 years.
This is what those fires looked like from Landsat's perspective:
Oct 22, North Park, Colorado. The East Troublesome fire near Granby dominated the news. In this particular image, its flames and smoke cloud command attention. Just north of East Troublesome, partially hidden by the smoke, is the Cameron Peak Fire. They got pretty cozy with each other. The Middle Fork Fire is paltry by comparison, tucked in the left hand edge of the tile. That's 2018's Silver Creek Fire at the bottom left.
I'm going to zoom in and share a time series of images from the Middle Fork Fire. Because of that night when the embers glowed on the horizon and looked too close. Because of that day we stood on Soda Mountain and watched smoke pouring from lodgepole pines like water falling skyward. Because of the teachers that obsessively watched the Air Quality Index to see if recess could be outside.
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DATASET: Landsat 8
LEARN: Google Earth Engine
The Middle Fork Fire progression
Landsat captured a total of 10 pictures of this fire. But half of them were too cloudy and obscured the fire. I ended up with five solid images that almost tell the fire's story from beginning to end. I cross-referenced these dates with reports in the Pilot & Today and the fire's official log on InciWeb to track its growth. There is a GIF of the series at the bottom.
Two weeks after a lightning strike ignited the Middle Fork Fire on Sept. 6 it had grown to more than 5,000 acres. Most of that growth occurred the day after it started. Then it steadily burned eastward, where you can see it surrounding the lakes of the North Fork of Mad Creek (Fish Hawk Lake, Mirror Lake, Lake Margaret) and reaching toward Luna Lake.
The day after this image was captured (Oct. 7), the fire was clocked at 10,000 acres. On October 8, a headline in the Pilot read, "People should not be panicked," likely because people were panicked.
This is where it gets interesting. Remember that early season snowstorm we were looking to for relief from the fire? Well, it looks here like the snow quieted it down.....
But one week later, it started making advances back toward the Northwest. Back closer to people. Snow wasn't necessarily the answer. It had reached almost its full size at this point: 20,433 acres.
The Middle Fork Fire, sleeping peacefully under a blanket of snow. Snow that, I promise, is white in real life, it's just turquoise here for reasons explained below. The fire was considered 100% contained as of December 15, but it's still smoldering and sizzling in the snow.
The Middle Fork Fire isn't over. The burn area will remain a part of our local experience, as it covers some of our favorite hikes and lakes in the Zirkels. It will teem with tiny life churning the rich soil. In 10 years or so the aspens will return, more abundant than before. Baby lodgepoles will fight them for sunlight and someday win. And other fires will burn on other ridges.
I'm in love with this satellite program. I don't expect you to love it. Because it's a satellite? But at least I hope you can take away a few things from my sappy obsession with it:
1. It's a monumental, beautiful accomplishment and should make you proud of the vastness of human potential.
2. It's not spying on you.
The basics: Landsat sensors are mounted on a series of satellites that orbit the Earth synchronized with the sun - so it's forever daytime - every 99 minutes. It covers the entire Earth in 16 days. Each pixel is 30m by 30m. The spatial resolution is important. This means it can't differentiate elements smaller than a 30m x 30m square. So it can't spy on you. Here's what it can spy on: the expansion of the human footprint, global carbon stores, polar ice caps, algae in lakes and rivers carving out their place. And while 30m resolution seem "blurry" to you, it's not blurry to scientists. That resolution on a global scale was, for a long time, considered incredible. These days, there are better resolution satellite programs with better coverage and faster return periods. But none with the consistency and longevity of Landsat, which has been running for more than 40 years. I love it because it can tell a story like no other Earth observation program can.
You might have some technical questions about the images I shared here. First of all, why are they cut off and what are those black edges? As the satellite passes over, Landsat's sensors' can "see" a path 115 miles wide. Those black parts denote the edge of a path. The images that would cover those black parts were captured on a different day and don't seamlessly match the tile I focused on. I may have cut them out because they're confusing, not important or cloudy.
Second, those colors look a bit off, don't they? Yes, because they are. Because Landsat has super powers. It can see outside the visible spectrum. It can sense near-infrared, short-wave infrared and thermal infrared. And so, instead of a true-color rendering, I produced...
False color composites
While we can't see all the wavelengths that Landsat can, we can translate them into an easily understandable eye language: RGB. In every image you see as you aimlessly scroll on your phone, each pixel carries a combination of 3 color channels: red, green and blue. If Landsat has interesting information to share that's not in the visible spectrum, we can choose to use that wavelength in the red, green or blue channels. Here's a secret: the burn scars you're seeing in the above photos don't really look like that. This is called a false color composite. In this case, it gives us slightly more information than if we were just skydiving over the Zirkels. Landsat's Band 7 reflects short-wave infrared (SWIR) wavelengths, and charred vegetation and soil reflect SWIR like crazy. So I mapped the SWIR band to the red channel, bringing those burn scars out in a deep, rusty red. The green channel is showing near-infrared (NIR), which brings out healthy vegetation in bright green. And the blue channel is showing true color blue. For more on how I did this and to try your hand at it yourself, see this month's tutorial on Github.