On-orbit calibration and performance of the EMIT imaging spectrometer
David R. Thompson, Robert O. Green, Christine Bradley, Philip G. Brodrick, N. M. Mahowald, Eyal Ben Dor, Matthew Bennett, Michael Bernas, Nimrod Carmon, K. Dana Chadwick, R. N. Clark, Red Willow Coleman, Evan Cox, Ernesto Diaz, Michael L. Eastwood, Regina Eckert, B. L. Ehlmann, Paul Ginoux, Marı́a Gonçalves Ageitos, Kathleen A. Grant, Luis Guanter, Daniela Heller Pearlshtien, Mark Helmlinger, Harrison Herzog, Todd M. Hoefen, Yue Huang, Abigail M. Keebler, О. В. Калашникова, Didier Keymeulen, Raymond F. Kokaly, Martina Klose, Longlei Li, S. Lundeen, John Meyer, Elizabeth M. Middleton, R. L. Miller, Pantazis Mouroulis, Bogdan Oaida, Vincenzo Obiso, Francisco Ochoa, Winston Olson-Duvall, Gregory S. Okin, T. H. Painter, Carlos Pérez García‐Pando, Randy Pollock, Vincent J. Realmuto, Lucas Shaw, Peter Sullivan, Gregg A. Swayze, Erik Thingvold, Andrew K. Thorpe, S. K. Santhana Vannan, Catalina Villarreal, Charlene Ung, Daniel W. Wilson, Sander Zandbergen
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.