CHAPS: A Compact Hyperspectral Imager for Air Pollution Remote Sensing

Air pollution is responsible for ~7 million premature deaths every year.  Current and planned low Earth orbit and geostationary satellite instruments have long provided global surveys, revealing pollution characteristics and trends.  We need a robust, sustainable observing strategy, however, for measuring the distribution of air pollution at high spatial and high temporal resolution.  The Compact Hyperspectral Air Pollution Sensor (CHAPS) incorporates technologies enabling a sustainable approach to air pollution observation from space.  CHAPS is a hyperspectral imager using freeform optics in a form factor suitable for accommodation on a small satellite or hosted payload.  It will make measurements of air pollution at unprecedented spatial resolution from low Earth orbit (1 x 1 km²) and will characterize, quantify, and monitor emissions from urban areas, power plants, and other anthropogenic activities.  The compact size and relatively lower cost of CHAPS makes a constellation feasible for the first time, with unprecedented spatiotemporal sampling of global point pollution sources.  NASA recently funded the development of a CHAPS–Demonstrator (CHAPS-D), which will result in an airborne demonstration of a CHAPS prototype instrument.  CHAPS derives heritage from the TROPOspheric Monitoring Instrument (TROPOMI) on the Sentinel-5 Precursor, which uses a freeform mirror telescope.  Freeform optics has potentially huge advantages over traditional optical designs, including fewer optical surfaces, less mass and volume, and improved image quality.  CHAPS-D combines a radiometrically calibrated freeform hyperspectral imager (300–500 nm @ 0.5-nm resolution) with associated detector and payload electronics within the design constraints of a 6U CubeSat.  We present the measurement requirements and preliminary design of CHAPS-D.