Stability Assessment of OCO-2 Radiometric Calibration Using Aqua MODIS as a...

Yu, S., R. Rosenberg, C. J. Bruegge, L. Chapsky, D. Fu, R. Lee, T. Taylor, H. Cronk, C. O'Dell, A. Angal, X. Xiong, D. Crisp, and A. Eldering (2020), Stability Assessment of OCO-2 Radiometric Calibration Using Aqua MODIS as a Reference, Remote Remote Sens., 2020, 1269, doi:10.3390/rs12081269.

With three imaging grating spectrometers, the Orbiting Carbon Observatory-2 (OCO-2) measures high spectral resolution spectra (λ/∆λ ≈ 19,000) of reflected solar radiation within the molecular oxygen (O2 ) A-band at 0.765 µm and two carbon dioxide (CO2 ) bands at 1.61 and 2.06 µm. OCO-2 uses onboard lamps with a reflective diffuser, solar observations through a transmissive diffuser, lunar measurements, and surface targets for radiometric calibration and validation. Separating calibrator aging from instrument degradation poses a challenge to OCO-2. Here we present a methodology for trending the OCO-2 Build 8R radiometric calibration using OCO-2 nadir observations over eight desert sites and nearly simultaneous observations from Moderate Resolution Imaging Spectroradiometer (MODIS) with sensor viewing zenith angles of 15 ± 0.5◦ . For the O2 A-band, this methodology is able to quantify a drift of −0.8 ± 0.1% per year and capture a small error in correcting the aging of the solar calibrator. For the other two OCO-2 bands, no measurable changes were seen, indicating less than 0.1% and less than 0.3% per year drift in the radiometric calibration of Band 2 and Band 3, respectively.

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