NASA's Airborne Sensor Facility MASTER Wildfire Monitoring

©NASA

San Francisco

On September 9th, 2020, Bay Area residents woke up to darkness. Acrid smoke blocked out the morning sun. The sky, dense with ash, turned a deep orange hue.

This apocalyptic glow was caused by widespread fires, exacerbated by land mismanagement and climate change. The weather in California is becoming hotter, drier and windier ‒ the perfect conditions for wildfires to thrive. Across the West, more than one million acres burned in October alone, making 2020's wildfire season the worst in U.S. history.

NASA has sensors onboard aircraft and satellites that collect data used to monitor our changing climate, as well as how agricultural land, forests and cities change over time. In October, despite COVID-19 disrupting much of airborne science, NASA's campaign to observe western U.S. ecosystems was given the go-ahead.

Instruments are operated jointly by JPL and the NASA Ames Airborne Sensor Facility (ASF) were loaded into a high-altitude ER-2 aircraft. MASTER is operated by ASF and the Airborne Visible / Infrared Imaging Spectrometer (or AVIRIS) instrument is operated by JPL. "The ER-2 is essentially like a 100 ft wing with a cockpit sitting on the front of it," says James Jacobson, senior manager for the ASF.

The ER-2 is a modified spy plane ‒ it reaches over 70,000 ft. The sensor systems, fitted into four pressurized compartments, can image Earth's surface and take spectral imaging to detect chemical signatures. From such altitudes, the information obtained by this flying laboratory is similar to satellite data.

Data collected by MASTER are the responsibility of Jacobson and the ASF team. He says, "One of the things that I like the most about the ASF is that it seems to have brought together engineers, scientists, data analysts and technicians of a very wide variety of backgrounds."

The ASF bridges the gap between airborne science and earth observation, helping researchers connect the sensors and aircraft they need to achieve a particular goal. Jacobson and his team calibrate the sensors, deploy and collect data, recalibrate, process the data and ultimately make it available to the science community.

Back in October, the ER-2's primary mission was to monitor land use but, as the aircraft flew over wildfires and copious smoke clouds, it caught the attention of the NASA Disasters Program. The Disasters team study wildfires and burn scars using data from many sources ‒ and the ASF is a data gold mine.

The facility's flagship sensor, called MASTER, is one of a kind. It images infrared radiation as well as light that is visible to the human eye.

"Light interacts with the chemistry of every surface it touches in different, and observable ways," Jacobson says. Researchers can use this information to determine the water content in vegetation, or even in soil, to study drought and damage to plant life.

Imagine you're looking at a field of lush, green grass. It looks green because all the light that isn't green is being absorbed by the grass. The green light is what's being reflected to your eyes. Jacobson says, "You can extrapolate that out to different parts of the solar spectrum."

"When you look at the light that bounces off of, say, a dry, arid field of dirt versus the light that bounces off of a wet field of dirt ‒ those are going to look very different in the spectral domain."

Researchers from the NASA Disasters Program wanted this data for two reasons. First, MASTER's infrared imaging allows researchers to look through the wildfire smoke. "The aerosol particles of the smoke don't absorb any light that MASTER is seeing in those [infrared] bands," Jacobson says.

Secondly, MASTER can take images in what's known as the 'thermal infrared' spectrum. This doesn't just penetrate cloud cover it creates an accurate heat map as wildfires (which can exceed 2,000°F) emit substantial infrared radiation.

Jacobson says, "Not only can we see the terrain, but we can also see what parts of the terrain have been affected in terms of vegetation loss, and we can very, very clearly image the leading edge of the fire because it's the hottest thing there."

This combination of visible, infrared and thermal data makes MASTER one of the most unique imaging sensors in airborne science. And it's been unrivalled for a long time. "MASTER has been flying since the 90s. And so it has a long legacy of data collection," Jacobson says. "Every year, there's talk like 'Oh, well, it might be time to retire MASTER, it's getting a little long in the tooth', but then we get data requests for it."

Since the early 2000s, the ASF has seen MASTER deployed on about a dozen different types of aircraft. Jacobson says, "We go through quite a bit of engineering in order to make sure that these instruments can be put on different kinds of airframes."

While MASTER has been designed to function at different altitudes, deploying on the ER-2 is not without risk. At 70,000 ft, the aircraft is flying in the top 5% of the Earth's atmosphere ‒ it's very close to outer space. Even though the cockpit is pressurized, the pilot has to wear what is essentially a space suit.

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