On-orbit calibration and performance of the EMIT imaging spectrometer

Creators: Thompson, David R.¹; Green, Robert O.¹; Bradley, Christine¹; Brodrick, Philip G.¹; Mahowald, Natalie²; Dor, Eyal Ben³; Bennett, Matthew¹; Bernas, Michael¹; Carmon, Nimrod¹; Chadwick, K. Dana¹; Clark, Roger N.⁴; Coleman, Red Willow¹; Cox, Evan⁵; Diaz, Ernesto¹; Eastwood, Michael L.¹; Eckert, Regina¹; Ehlmann, Bethany⁶; Ginoux, Paul⁷; Ageitos, María Gonçalves^{8, 9}; Grant, Kathleen¹⁰; Guanter, Luis¹¹; Pearlshtien, Daniela Heller³; Helmlinger, Mark¹; Herzog, Harrison¹; Hoefen, Todd⁵; Huang, Yue^{12, 13}; Keebler, Abigail⁶; Kalashnikova, Olga¹; Keymeulen, Didier¹; Kokaly, Raymond⁵; Klose, Martina¹²; Li, Longlei²; Lundeen, Sarah R.¹; Meyer, John⁵; Middleton, Elizabeth¹⁴; Miller, Ron L.^{13, 15}; Mouroulis, Pantazis¹; Oaida, Bogdan¹; Obiso, Vincenzo^{8, 13}; Ochoa, Francisco¹⁶; Olson-Duvall, Winston¹; Okin, Gregory S.¹⁶; Painter, Thomas H.^{16, 17}; Pérez García-Pando, Carlos^{8, 18}; Pollock, Randy¹⁹; Realmuto, Vincent¹; Shaw, Lucas¹; Sullivan, Peter¹; Swayze, Gregg⁵; Thingvold, Erik¹; Thorpe, Andrew K.¹; Vannan, Suresh¹; Villarreal, Catalina¹; Ung, Charlene¹; Wilson, Daniel W.¹; Zandbergen, Sander¹

1. Jet Propulsion Lab
2. Cornell University
3. Tel Aviv University
4. Planetary Science Institute
5. United States Geological Survey
6. California Institute of Technology
7. Geophysical Fluid Dynamics Laboratory
8. Barcelona Supercomputing Center
9. Universitat Politècnica de Catalunya
10. University of Southern California
11. Universitat Politècnica de València
12. Karlsruhe Institute of Technology
13. Goddard Institute for Space Studies
14. Goddard Space Flight Center
15. Columbia University
16. University of California, Los Angeles
17. Airborne Snow Observatories, Inc., Mammoth Lakes, CA, USA
18. Institució Catalana de Recerca i Estudis Avançats
19. Victoria University of Wellington

Abstract

The Earth surface Mineral dust source InvesTigation (EMIT) is a remote visible to shortwave infrared (VSWIR) imaging spectrometer that has been operating onboard the International Space Station since July 2022. This article describes EMIT's on-orbit spectroradiometric calibration and validation. Accurate spectroscopy is vital to achieve consistent mapping results with orbital imaging spectrometers. EMIT takes a unique approach to this challenge, with just six optical elements, no shutter, and no onboard calibration systems. Its simple design focuses on uniformity and stability to enable vicarious spectroradiometric calibration. Our experiments demonstrate that this approach is successful, approaching the fidelity of manual field spectroscopy in some cases, and enabling new and more accurate products across diverse Earth science disciplines. EMIT achieves several notable firsts for an instrument of its class. It demonstrates successful on-orbit adjustments of Focal Plane Array (FPA) alignment with sub-micron precision. It offers spectral uniformity better than 98%. Optical artifacts in the measurement channels are at least three orders of magnitude below the primary solar-reflected surface signals. Its noise performance enables percent-level discrimination in the depths of mineral absorption features. In these aspects, EMIT satisfies the stringent performance needs for the next generation of VSWIR imaging spectrometers to observe the Earth's ecosystems, geology, and water resources.

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Acknowledgement

EMIT is supported by the National Aeronautics and Space Administration Earth Venture Instrument program, under the Earth Science Division of the Science Mission Directorate. K. Dana Chadwick is supported by the NASA Applied Sciences Program. Carlos Pérez García-Pando and María Gonçalves Ageitos acknowledge support from the European Research Council (ERC) Consolidator Grant FRAGMENT (grant agreement No. 773051), and the AXA Chair on Sand and Dust Storms at the Barcelona Supercomputing Center funded by the AXA Research Fund. Martina Klose has received funding through the Helmholtz Association's Initiative and Networking Fund (grant agreement No. VH-NG-1533). We thank Jeffrey Czapla-Myers and the University of Arizona team for their maintenance and operation of the Railroad Valley automated calibration facility. This research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. We acknowledge the support and assistance of NASA's International Space Station Program. The USGS authors' contribution to this published Work was prepared by U.S. federal government employees as part of their official duties and constitutes a “work of the United States government,” and is considered to be in the public domain and therefore domestic copyright does not apply. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Copyright 2024 California Institute of Technology. All rights reserved. US Government Support Acknowledged.

Contributions

David R. Thompson: Conceptualization, Formal analysis, Investigation, Methodology, Software, Validation, Writing – original draft, Writing – review & editing. Robert O. Green: Conceptualization, Investigation, Methodology, Project administration, Resources, Supervision. Christine Bradley: Formal analysis, Investigation, Methodology. Philip G. Brodrick: Data curation, Investigation, Methodology, Writing – original draft, Writing – review & editing. Natalie Mahowald: Conceptualization, Funding acquisition, Project administration, Supervision, Writing – original draft. Eyal Ben Dor: Conceptualization, Investigation, Methodology. Matthew Bennett: Formal analysis, Investigation, Methodology, Supervision. Michael Bernas: Formal analysis, Investigation. Nimrod Carmon: Formal analysis, Investigation, Methodology, Software. K. Dana Chadwick: Investigation, Methodology, Supervision, Writing – original draft. Roger N. Clark: Conceptualization, Investigation, Methodology, Validation. Red Willow Coleman: Formal analysis, Investigation, Software, Validation. Evan Cox: Data curation, Investigation, Methodology, Writing – original draft. Ernesto Diaz: Investigation, Supervision. Michael L. Eastwood: Conceptualization, Formal analysis, Investigation, Methodology, Project administration, Writing – original draft. Regina Eckert: Formal analysis, Investigation, Methodology, Software, Writing – original draft. Bethany L. Ehlmann: Conceptualization, Investigation, Methodology, Supervision, Writing – original draft. Paul Ginoux: Conceptualization, Investigation, Validation. María Gonçalves Ageitos: Investigation, Writing – original draft. Kathleen Grant: Formal analysis, Investigation, Software. Luis Guanter: Conceptualization, Methodology, Writing – original draft. Daniela Heller Pearlshtien: Data curation, Investigation, Validation, Writing – original draft. Mark Helmlinger: Data curation, Formal analysis, Investigation, Methodology. Harrison Herzog: Formal analysis, Investigation. Todd Hoefen: Data curation, Investigation, Methodology, Validation. Yue Huang: Investigation, Methodology. Abigail Keebler: Data curation, Formal analysis, Investigation, Methodology, Validation. Olga Kalashnikova: Conceptualization, Methodology. Didier Keymeulen: Investigation, Methodology, Writing – original draft. Raymond Kokaly: Formal analysis, Investigation, Methodology, Validation, Writing – original draft. Martina Klose: Investigation, Validation, Writing – original draft. Longlei Li: Investigation, Validation. Sarah R. Lundeen: Investigation, Software, Supervision. John Meyer: Data curation, Investigation, Validation. Elizabeth Middleton: Conceptualization, Methodology. Ron L. Miller: Conceptualization, Methodology, Validation. Pantazis Mouroulis: Conceptualization, Formal analysis, Investigation, Methodology, Supervision. Bogdan Oaida: Formal analysis, Investigation. Vincenzo Obiso: Investigation, Validation, Writing – original draft. Francisco Ochoa: Data curation, Investigation, Methodology, Software, Validation. Winston Olson-Duvall: Investigation, Software. Gregory S. Okin: Conceptualization, Formal analysis, Investigation, Methodology, Validation. Thomas H. Painter: Conceptualization, Investigation, Resources. Carlos Pérez García-Pando: Conceptualization, Investigation, Methodology, Writing – original draft. Randy Pollock: Conceptualization, Investigation, Project administration. Vincent Realmuto: Conceptualization, Investigation, Methodology. Lucas Shaw: Formal analysis, Investigation. Peter Sullivan: Formal analysis, Investigation. Gregg Swayze: Conceptualization, Data curation, Investigation, Methodology, Validation. Erik Thingvold: Formal analysis, Investigation. Andrew K. Thorpe: Investigation, Methodology, Writing – original draft. Suresh Vannan: Supervision. Catalina Villarreal: Project administration. Charlene Ung: Supervision, Writing – original draft. Daniel W. Wilson: Formal analysis, Investigation. Sander Zandbergen: Formal analysis, Investigation.

Data Availability

The EMIT science data system code, including the level 1b radiance calibration and associated calibration files, can be found at https://github.com/emit-sds/. Spectral libraries used in the surface/atm fits are downloadable from the ECOSIS library at https://ecosis.org/package/emit-manually-adjusted-snow-and-liquids-reflectance-spectra, https://ecosis.org/package/emit-manually-adjusted-vegetation-reflectance-spectra, and https://ecosis.org/package/emit-manually-adjusted-water-reflectance-spectra.

Additional Information

The USGS authors' contribution to this published Work was prepared by U.S. federal government employees as part of their official duties and constitutes a “work of the United States government,” and is considered to be in the public domain and therefore domestic copyright does not apply. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Copyright 2024 California Institute of Technology. All rights reserved. US Government Support Acknowledged.

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