Cutting-Edge Sensor Flies into Earth Science
Airborne infrared hyperspectral imaging may sound like a 12-syllable piece of technobabble, but it’s actually a useful technology that the military has employed for years. It involves flying a sensor over an area to collect data on the thermal infrared radiation (heat) that is emitted by the land and atmosphere below.
“It turns out that different chemical compounds absorb different wavelengths of light,” said Dr. George Scherer, director of the Imaging Spectroscopy Department. “By analyzing the pattern that we see … I can tell you what the materials on the ground are; I can tell you what the gases are in the atmosphere.”
While the military uses this capability to, for example, spot vehicles on the ground, there are certainly many other applications. Aerospace is therefore looking to expand its airborne infrared hyperspectral imaging capabilities into earth science applications, such as mineral mapping, global warming studies, and crop health analysis.
Recently Aerospace took a sensor known as Mako on a series of test flights over California and into Nevada to collect data on industrial sites, agricultural areas, and other locations of interest. Mako is a cutting-edge sensor that the team sees as the first in a new generation of this type of sensor.
“There’s really nothing like it right now,” Scherer said. “It really is a step beyond what anyone else has built.”
Aerospace’s work with these sensors stretches back to the 1990s, when a team led by Dr. John Hackwell built the Spatially Enhanced Broadband Array Spectrograph System, or SEBASS. The endeavor grew to include personnel from the Space Science Applications Laboratory, the Sensor Systems Subdivision, and the Advanced Technology Division. Aerospace and others have since developed other sensors, but they don’t go much beyond the capability of SEBASS.
“Somewhere in the 2006 frame, we looked back and realized all these sensors that have been built were for the most part reworks of SEBASS, so we went to [Aerospace management] and basically recommended a corporate research initiative to build the next generation sensor, because it doesn’t look like anybody else is,” Scherer said. “And so that’s how Mako came about.”
The idea was approved and the team spent about four years building Mako, which has now been flown on three series of flights.
Previous sensors used a “push-broom scan” where the sensor essentially stares directly beneath the plane. Mako, on the other hand, uses a “whisk-broom scan” and collects data up to 45 degrees either side of the flight line. “The increase in data rate is of the order of 50x,” said Dr. David Tratt, the principal investigator of the earth science program.
In fact, Mako collects so much more information than previous sensors that the data analysis tools can’t keep up. “What this has done is it has basically overflowed our data processing chain,” Scherer said.
So they are looking at ways to improve the data analysis to match Mako’s collection rates. In the meantime, they are working to demonstrate its uses in nonmilitary applications. Over a one-week period, they collected data from a number of different sites, looking at everything from a geothermal field to oil seeps to the San Andreas Fault.
They flew the sensor in a Twin Otter plane at an altitude of about 10,000-12,000 feet above the ground. Several members of the team operated the equipment on each flight, braving the vibrating, non-pressurized plane, and even using oxygen at higher altitudes. The team was specifically looking for methane, which is a greenhouse gas of great interest to the climate change science community. However, the team also collected a wide range of other data.
In southern Nevada, for instance, they surveyed the proposed site of a solar energy farm to assess the surface temperature distribution and types of vegetation present. The intent is to include the findings of this survey in an environmental impact statement that is to be evaluated before the solar farm is approved.
They flew over the Central Valley, home of intensive agriculture and dairy farming. “The combination of all of those activities gives rise to one of the strongest ammonia hotspots globally,” Tratt said. “We see that very clearly in our data.”
At the request of the U.S. Geological Survey, the team collected data over the Hector Mine Fault, source of an earthquake in 1999.
They measured emissions from a variety of industrial sites in the Los Angeles Basin, as well as the national petroleum reserve in Elk Hills.
They also surveyed a rare earth mine in eastern California. “We’re hoping to be able to characterize the same rock formations that they’re currently exploiting and detect similar formations in neighboring terrain to demonstrate the value of our techniques for mineral prospecting,” Tratt said.
They even took the plane out over the ocean, anticipating that their technology would be able to find small boats in search and rescue situations. This could be particularly helpful at night because they are looking at the infrared portion of the spectrum rather than the visible. “We consider it unsporting to work with light that you can actually see with your eyes,” Scherer quipped.
All of these applications have the potential to be beneficial. What may be less obvious is that some of these earth science applications may also tie back to national security.
“In recent years natural disaster events in the U.S. and the world at large have sharpened the focus on earth system science to the point where it is now recognized at [federal] executive, congressional, and DOD/IC levels as having important national security ramifications,” Tratt said.
Thus, Mako will be serving the national security even as it ventures into civil and commercial arenas. And the Aerospace team enjoys the work, as they benefit all of these different areas. Tratt described the feeling of being in the plane with the sensor:
“It’s noisy. It can be cold. But overall, you cannot really beat the sensation of being out in the field with your instruments, making actual measurements of the world around you,” he said. “So we find it very satisfying.”