A New, Compact Hyperspectral Imager for Targeted Air Pollution Remote Sensing

The Compact Hyperspectral Air Pollution Sensor (CHAPS) is a new CubeSat instrument for targeted air pollution remote sensing, with unprecedented spatial resolution from low Earth orbit and the goal of science-quality trace gas measurements, akin to OMI and TROPOMI. The NASA Earth Science Technology Office has funded the development of a CHAPS demonstrator (CHAPS-D), which will result in ground-based (end of 2023) and airborne demonstrations (2024) of a CHAPS prototype instrument. Current low Earth orbiting and geostationary satellite observatories provide global surveys of air quality characteristics and trends. Scientists and policymakers, however, need environmental information at spatial and temporal resolutions comparable to known variability: diurnally and at sub-urban scale. Targeted pollution observations at such spatial and temporal resolutions could better characterize, quantify, and monitor emissions from urban areas, power plants, and other anthropogenic activities, with both scientific and societal benefits. The miniaturization of CHAPS-D is possible using freeform optics, with heritage from TROPOMI through collaboration with TNO (The Netherlands), and additive manufacturing. The instrument measures solar backscattered radiance at 300–500 nm (@ 0.6-nm spectral resolution) at 1 x 1 km2 spatial resolution from low Earth orbit or 20-m resolution from an aircraft. Trace gas retrievals are made using established differential optical absorption spectroscopy techniques, focusing primarily on NO2 but with other species also possible, such as formaldehyde and SO2. CHAPS would complement existing and future trace gas surveyors, such as TROPOMI and TEMPO. As a constellation or in combination with the larger satellites, CHAPS would address such issues as the short-term evolution of pollution, turbulent mixing of air pollution plumes, “top-down” quantification of point-source emissions, and pollution transport and chemical processing. We present the science context, measurement requirements, and design of CHAPS-D, as well as results from laboratory (and perhaps ground-based) testing.