NASA’s CHAPS instrument may help measure air pollution with greater accuracy
May 8, 2023 – More than 80% of people living in urban areas breathe air dangerously saturated with pollutants, according to the World Health Organization, and improving urban air quality is a top priority for public health experts across the country.
NASA’s new Compact Hyperspectral Air Pollution Sensor (CHAPS) instrument could help those experts measure air pollution more effectively. Featuring a novel configuration of freeform optics housed within a 3D-printed aluminum architecture, the instrument – which fits aboard a 6U CubeSat – produces hyperspectral data more precise than was previously possible using small satellites.
The miniaturized hyperspectral imager is only slightly larger than a cereal box, but it could characterize air polluting gases with the unprecedented spatial resolution of one square kilometer per pixel – an area less than one-tenth the size of Disney World.
Data sets with such detailed spatial resolution produced by cost-efficient CubeSats would help public health experts better understand where certain air pollutants come from – for example, specific power plants or high-traffic thoroughfares – and develop new solutions for protecting vulnerable communities from those pollutants.
“One of the frontiers of air pollution is higher spatial and temporal resolution on the ground, and that is driven, in part, by public health. Talk to public health experts trying to understand air pollution, and they’ll tell you getting to finer spatial resolution and temporal resolution is urgent,” said William Swartz, atmospheric scientist at the Johns Hopkins University Applied Physics Laboratory and Principal Investigator for CHAPS.
Swartz explained how he and his team wanted to not only provide researchers with improved hyperspectral data describing air pollution, but also create an instrument that was less expensive to produce compared to traditional space-based spectrometers.
To improve data resolution and reduce the size of their instrument, they used an emerging technology called freeform optics. While other spectrometers, such as TROPOMI, also use these small, asymmetrical mirrors to observe air pollution from outer space, CHAPS is the first instrument to sport an optical system made up entirely of these unique optical elements.
“Freeform optics, essentially, allow us to do corrections of optical aberrations with fewer optical elements, and you can also pack them tighter as well without compromising the overall optical performance of the instrument,” Swartz said.
They also utilized additive manufacturing, also known as 3D printing, to create a custom, cost-efficient aluminum shell to house their optics configuration. Specifically, they used an additive manufacturing technique called topology optimization to produce their housing as efficiently as possible.
“Topology optimization is a mathematical approach to basically determine where material is needed and where it’s not needed, so you get this organic-looking structure that reduces mass” said Swartz.
Creating a structure fit for holding freeform optics precisely aligned through the rigors of space launch that can also be produced with additive manufacturing was no easy task, but the effort will return dividends. Future iterations of CHAPS could be manufactured with the press of a button, dramatically reducing the cost and complexity of production.
With NASA’s King Air B200 twin-engine aircraft, Swartz and his team will use CHAPS to measure atmospheric nitrogen dioxide – a common air pollutant. Another NASA project, the “Intelligent Long Endurance Observing System,” plans to show how CHAPS could be used to measure pollution from aboard a high-altitude, low-orbit drone.
CHAPS is still in development, but Swartz and his team are hard at work preparing their instrument for a future space validation mission, which will pave the way for constellations of CHAPS-equipped small satellites.
Gage Taylor, NASA Earth Science Technology Office