Miniature Hyperspectral Infrared Instruments and Observing Methods for Next-generation Vertical Profile Observations of the Temperature, Water Vapor, and Vertically Resolved Horizontal Wind Fields within a Distributed LEO Observing System

Hyperspectral infrared sounding observations of the temperature and water vapor vertical profiles from low earth orbit have supported critical advances in our understanding of the of the earth system, and are currently among the highest impact observations assimilated into our numerical weather prediction models. However, future advances in atmospheric science and next-generation higher temporal and spatial resolution numerical weather models will need these observations more frequently, and at much higher horizontal resolution. Miniature IR sounding instruments employed in LEO constellations of micro-satellites would provide an affordable path to these higher resolution observations.

MISTiC^® Winds is an instrument and constellation mission approach to simultaneously observe the global thermodynamic state and the vertically resolved horizontal wind field in the troposphere from LEO SSO using an affordable constellation of ESPA-class micro-satellites. The MISTiC instrument is a wide-field imaging dispersive spectrometer operated in the 4.05-5.75 micrometer band, with the spectral resolution, sampling, radiometric sensitivity, and stability needed to provide temperature and water vapor soundings of the troposphere, with 1 km vertical resolution in the -comparable to those of NASA’s Atmospheric Infrared Sounder in the troposphere. The MISTiC instrument and constellation observing method were developed under the NASA Instrument Incubator program, which included instrument and observation method development, laboratory testing, and an airborne demonstration of the observing method and spectrometer on a NASA ER2 [1]. A recent assessment shows that this wind observing method would satisfy the key wind vertical profile observation requirements identified by NOAA and the 2017 ESAS-Decadal Survey.

The LISSTiC instrument concept was developed more recently as part of a pre-phase-A study for NOAA’s next generation observing system architecture. The spectral channels in LISSTiC complement those of MISTiC by extending temperature and moisture vertical profiling into the stratosphere, by providing complementary sounding of temperature in the troposphere to provide cloud-cleared spectral radiances in partly cloudy fields, and by providing observations of ozone and other trace gases that are not well observed within the MISTiC spectral range. Together, these instruments would meet the IR spectral sounding instrument requirements originally developed by NASA and NOAA for GOES-R-HES program. Their projected performance characteristics are consistent with those identified in the recent NOAA LEO/GEO BAA for both tropospheric and stratospheric sounding for NOAA’s next generation observation architecture.

The MISTiC instrument concept has been described previously [1], and has recently been updated so that all of its components and most major assemblies are at TRL-6 or greater. Its design was also used as a point of departure for the design of LISSTiC, which provides hyperspectral coverage in the 9-14.7 micrometer band. The LW/VLWIR LISSTIC instrument is slightly larger than the MWIR MISTiC instrument, with somewhat higher (but still modest) power demand due to the cooling requirements of very long cutoff wavelength infrared detector arrays. It is also composed of TRL-6 or higher components. Each of these instruments have much higher spatial resolution, (<3 km at nadir for MISTiC from 800 km orbit), and finer spatial sampling than current hyperspectral sounders. Studies show that these can be accommodated together on a single ESPA-class micro-satellite, or flown separately as elements in a disaggregated observing architecture.

For MISTiC, a sequence of hyperspectral observations from several micro-satellites in an orbital plane with short time separation would provide hyperspectral motion vector winds observations with global coverage in addition to the tropospheric thermodynamic vertical profiles. Some of these MISTiC instruments could be accompanied by a LISSTiC instrument to provide observations of the more slowly changing stratosphere. Low fabrication and launch costs enable a constellation of such instruments to provide more frequent atmospheric observations than current-generation sounders provide, at much lower mission cost. This approach would provide a valuable new capability for the study of the processes driving high-impact weather events, and critical high resolution observations needed for future numerical weather prediction.

References

[1] Maschhoff, K.; Polizotti, J.; Aumann, H.; Susskind, J.; Bowler, D.; Gittins, C.; Janelle, M.; Fingerman, S. Concept Development and Risk Reduction for MISTiC Winds, A Micro-Satellite Constellation Approach for Vertically Resolved Wind and IR Sounding Observations in the Troposphere. Remote Sens. 2019, 11, 2169. https://doi.org/10.3390/rs11182169