The Nano-satellite Atmospheric Chemistry Hyperspectral Observation System (NACHOS) is a high-throughput (f/2.9), high spectral resolution (~1.3 nm optical resolution, 0.6 nm sampling) Offner-design hyperspectral imager operating in the 300-500 nm spectral region. The 1.5U instrument payload (1U optical system, 0.5U electronics module) is hosted by a 1.5U LANL-designed CubeSat bus to comprise a 3U complete satellite. Spectroscopically similar to NASA’s Ozone Monitoring Instrument (OMI), which provides wide-field global mapping of ozone and other gases at coarse spatial resolution, NACHOS fills the complementary niche of targeted measurements at much higher spatial resolution. With 350 across-track spatial pixels and a 15-degree across-track field of view, NACHOS will provide spectral imaging at roughly 0.4 km per pixel from 500 km altitude. NACHOS incorporates highly streamlined gas-retrieval algorithms for rapid onboard processing, alleviating the need to routinely downlink massive hyperspectral data cubes. We will discuss the instrument design, challenges in achieving mechanical robustness to launch vibration in such a compact instrument, the onboard calibration system, and gas-retrieval data downlink strategy. We will also discuss potential science missions, including monitoring of NO2 as an easily detected proxy for anthropogenic fossil-fuel greenhouse gases, monitoring lowlevel SO2 degassing at pre-eruptive volcanoes, H2CO from wildfires, and characterization of aerosols. The long-term vision is for a many-satellite constellation that could provide both high spatial resolution and frequent revisits for selected targets of interest. As an initial technology demonstration of this vision, the NACHOS project is currently slated to launch two CubeSats in early 2022.
Hyperspectral imaging with sufficient resolution and sensitivity for scientifically useful space-based mapping of trace gases has long required large and expensive satellite instruments. Miniaturizing this capability to a CubeSat configuration is a major challenge, but opens up more agile and far less expensive observing strategies. A major step in this direction is our development of NACHOS, an ultra-compact (1.5U instrument, 3U complete CubeSat) hyperspectral imager covering the 300-500nm spectral range in 400 channels. Here we describe laboratory and field performance characterization of this new instrument. Laboratory tests demonstrate spatial and spectral resolutions of <0.8 mrad and 1.3 nm, respectively, with good resolution of the spectral lines of our SO2 and NO2 target gases. Outdoor field tests under realistic illumination conditions provide real-world signal-to-noise benchmarks, and yield hyperspectral images displaying high quality solar and atmospheric spectra. To estimate on-orbit gas retrieval sensitivities, we computationally implanted plumes of varying concentrations into acquired hyperspectral datacubes. Applying our adaptive matched filter gas-retrieval algorithms to the generated scene, we predict NACHOS will be able to distinguish 35 and 7 ppm⋅m plumes of SO2 and NO2 (respectively) with high sensitivity; a capability well-suited to address scientific goals related to monitoring both passive SO2 degassing from volcanoes and NO2 emissions from anthropogenic sources. Lastly, we will show findings from thermal and vibrational environmental tests, performed in preparation for a scheduled early-2022 launch, demonstrating the extremely robust spectrometer design is well-suited for satellite-based deployment.
We describe the development and implementation of plume detection algorithms under severe bandwidth and processing constraints imposed by a CubeSat architecture. In particular, two ideas will be presented: one employs onboard processing to reduce the data that is downlinked, and one employs the Sparse Matrix Transform (SMT) to speed up the onboard computation of an approximate Mahalanobis distance.
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