LAUSR

The Orbiting Carbon Observatory-3 (OCO-3) measures carbon dioxide and solar-induced fluorescence from the International Space Station (ISS). It uses the flight spare spectrometers from its predecessor, OCO-2, and produces spectral images in three near-infrared channels. Its preflight radiometric calibration was performed at the National Aeronautics and Space Administration’s (NASA) Jet Propulsion Laboratory and is constantly updated inflight to account for both gradual and abrupt changes in instrument response that display a wavelength dependence within the bands. Some of these are caused by the accumulation of contaminants and their subsequent removal after scheduled decontamination events, but sudden changes of the overall gain state of the two longest wavelength bands, unrelated to contamination, are also observed. They were found to be triggered by instrument resets as well as by decontamination events. OCO-3 cannot perform solar calibration due to its position on the ISS and the inflight updates to its radiometric calibration depend solely on its on-board calibrator, which consists of three lamps and a reflective diffuser. The lamps are observed with different cadences and thus degrade at different rates. Information from all three lamps is combined to provide high temporal resolution and minimize the impact of lamp aging on the gain degradation coefficients that describe the changes in the radiometric response of the instrument inflight. We use thousands of soundings from ocean scenes to assess the relative calibration within the two shortest wavelength bands. Here we present the algorithm developed for the inflight relative radiometric calibration of OCO-3 Version 10 products and discuss the state of the calibration.