CubeSat-Based High-Resolution Hyperspectral Imagers for Atmospheric Trace Gas Monitoring

High-resolution imaging spectrometers, also known as hyperspectral imagers (HSI’s), offer the ability to image and quantify atmospheric trace gases from space with high sensitivity. This capability is of great value to a wide range of earth sciences, from atmospheric science and climate change, to biosphere monitoring and volcanology. The required combination of high spectral resolution and high sensitivity necessary for scientifically useful measurements, however, has until recently put trace-gas HSI beyond the realm of CubeSat-based instruments. Not only are HSI instruments typically large and heavy, but they also generate huge volumes of data that must undergo detailed analysis to extract and interpret the gas signatures of interest, something traditionally requiring the high downlink bandwidth only available on large satellite platforms. But a great deal of miniaturization is in fact possible without sacrificing optical performance, and the data volume problem can be addressed with smart on-board processing strategies. We are currently building an ultra-compact hyperspectral imager designed to mate with LANL’s highly successful CubeSat bus, the integrated HSI payload and bus comprising a 3U system. Operating in the 300-500 nm spectral region, with f/2.3 optics, 0.6 nm spectral resolution, 320 spectral channels, and 320 across-track spatial pixels, the instrument will target NO₂, SO₂, O₃, CH₂O, and other gases, as well as aerosols, with sufficient spectral resolution to reliably separate trace gas signatures from the atmospheric background. It is spectroscopically similar to NASA’s Ozone Monitoring Instrument (OMI) but is aimed at much higher spatial resolution, narrow field-of-view targeted observations (~130 km swath width and 0.4 km pixel resolution from 500 km altitude). Missions include monitoring fossil fuel burning and low-level passive degassing at volcanoes. To address the key issue of the CubeSat downlink bottleneck, we have developed streamlined on-board HSI gas retrieval algorithms that run many times faster than traditional methods. Initial tests on OMI data demonstrate these algorithms can achieve sensitivity comparable to more exhaustive standard approaches, but with execution times on our CubeSat on-board processor reduced from several hours to tens of minutes for a typical large-area data set. With this instrument as a first demonstration, we seek to enable a paradigm shift in spaceborne trace gas spectral imaging, from expensive single-platform instruments, to agile constellations of relatively inexpensive instruments on small satellites. Such constellations could be tailored to offer much more favorable combinations of spatial resolution and revisit time than can be achieved by any single instrument.