An Eruption through Several Spectrums

Few Earth observation satellites were on orbit when I conducted research for my master’s thesis in geology in the mid-1990s, when remote sensing as a discipline was just taking off. It was novel to have satellite imagery of a volcanic eruption to analyze. It was even rarer to have multiple satellite sensors collect data of a single eruption event. I was lucky enough to study a large eruption from the volcano Láscar in Chile through both NOAA’s Advanced Very High Resolution Radiometer (AVHRR) sensor and NASA’s Total Ozone Mapping Spectrometer (TOMS) sensor, which captured volcanic ash clouds.

Today, there are many satellites circling the planet with the capability to image volcanic events.  We are fortunate at DigitalGlobe to own and operate the highest resolution commercial satellites, including one that has the only shortwave infrared (SWIR) sensor. These satellites and their spectral bands have been hard at work imaging Kilauea’s ongoing eruption in Hawaii, giving us unique insight into situations on the ground and how volcanoes work:

Natural color imagery

By viewing imagery in natural color (the way the human eye sees the world), such as in the above May 20, 2018 image of just east of the Leilani Estates neighborhood from our WorldView-2 satellite, we can begin to identify locations around the volcanic activity where the vegetation is being affected: it is brownish (indicating unhealthy and dying plants) and near brighter green areas (healthy plants). These changes can be an early indicator of volcanic activity because they are primarily driven by heat changes underground and toxic gases released by the lava.

Near Infrared (NIR) imagery

This image is the same WorldView-2 image used for the natural color example, but we’re looking at it with different light bands, specifically the NIR bands. NIR imagery provides further insightful information about vegetation health. Here, healthy vegetation can be seen as bright red. That’s because the light bands reflect brightly off leaves with high chlorophyll levels (healthy plants) than leaves with low chlorophyll levels (unhealthy or dead plants), indicated by the muted red color. The brown and black areas signal dead vegetation or areas of exposed soil and rock.  In the image above, the super bright red spots are exposed lava that’s very hot. The lava flows appear black because it’s exposed rock.

Shortwave Infrared (SWIR) imagery

DigitalGlobe is the only provider of commercial satellite-based SWIR imagery – eight unique bands of light that cannot be seen by the human eye! By using the SWIR bands on our WorldView-3 satellite, shown in the image above of Kilauea’s east rift zone, we can see the extent of active areas because SWIR light bands are sensitive to thermal emissions that do not register in natural color or NIR imagery. Hot spots and lava tubes, which appear to be cool or non-active in natural color imagery, are easily identified with SWIR – they pop out in the brightest colors. Lava tubes can transport lava many miles away from their source, so SWIR imagery allows the active lava tubes to be quickly located and mapped, empowering first responders to know where to issue evacuation orders and be prepared to react to potential fires.  The hot areas and relative temperatures can be determined through haze, smoke and dust, but cannot be seen through water vapor or clouds, as is evident in the image above.

SWIR is not limited to only telling us about heat. It can also provide information about a multitude of other things like: the materials on the ground (what different roofs are made of in a city, for example, or what indicator minerals are present on a mountain), soil moisture (like determining whether crops need more or less irrigation), man-made materials (paints and plastics) and maritime wake index (showing where a boat came from).

This natural color image (showing green vegetation) and color infrared image (showing the vegetation in red) reveal how using different spectral bands unveils the location of lava tubes running to the ocean. These images were taken on May 23, 2018 using DigitalGlobe’s WorldView-2 satellite.

The different spectral bands on DigitalGlobe’s satellites, combined with the resolution and accuracy capabilities, provide a wide array of information that enable our customers and partners to have the most current and accurate information at their fingertips when they’re making decisions, sometimes in life and death situations.

 

Heather Shocker earned a M.S. in Geology at Michigan Technological University, focusing on volcanology through remote sensing techniques. Afterwards, she volunteered as a Visiting Scientist with New Zealand’s Institute of Geological and Nuclear Science, which monitors the country’s active volcanoes, to share her knowledge of remote sensing as it relates to volcanology. She’s now a member of DigitalGlobe’s International Defense and Intelligence team.