Radiometric Calibration Analysis from OCO-3 and OCO-2 Simultaneous Nadir Overpasses
Thomas P Kurosu, JPL, thomas.kurosu@jpl.nasa.gov (Presenter)
Shanshan Yu, JPL, shanshan.yu@jpl.nasa.gov
Robert Alan Rosenberg, JPL, rob.rosenberg@jpl.nasa.gov
Annmarie Eldering, Jet Propulsion Laboratory / Caltech, annmarie.eldering@jpl.nasa.gov
Gary Spiers, JPL, gary.d.spiers@nasa.gov
David Crisp, JPL/Caltech, david.crisp@jpl.nasa.gov
The Orbiting Carbon Observatory 3 (OCO-3) was launched to the International Space Station (ISS) in May 2019 and has been making routine measurements since early August 2019. OCO-3 records reflected sunlight in the near-InfraRed spectral region to estimate the column average CO2 dry air mole fraction (XCO2) and solar-induced chlorophyll fluorescence (SIF). Originally built as the spare copy of the OCO-2 flight instrument, OCO-3 shares most hardware characteristics with the OCO-2 spectrometer. Aside from an added polarizer and a telescope with smaller blur spot, major differences are limited to external modifications like the pointing mirror assembly that was added to OCO-3 to accommodate operation on the ISS.
An important difference of instrument operations between OCO-2 and OCO-3 is that, unlike OCO-2, OCO-3 is unable to perform direct solar observations, a limitation that is imposed by OCO-3’s installation location on the ISS. This has consequences for in-flight radiometric calibration. Aside from pre-flight thermal vacuum testing, on-board calibration lamps, and lunar observations, OCO-3 has to rely on vicarious- and cross-calibration, including measurements over well-characterized surface sites and radiometric comparison with independent satellite sensors. The similarity of the OCO-2 and OCO-3 spectrometers makes OCO-2 the ideal candidate for cross-comparison of continuum radiances to establish radiometric accuracy.
Over the current course of the OCO-3 observation record, about 300 incidences of OCO-2/3 near-Simultaneous Nadir Observations (SNOs) – i.e., both instruments recording measurements in nadir mode over the same position on the Earth within 10 minutes of each other – have been identified. These occur mainly around 50º N/S, where the ISS ground track changes between ascending and descending node and the OCO-2 and OCO-3 ground tracks are thus at their largest relative angle. We report on how we determine and select SNO incidents, and present results from radiometric comparisons of co-located OCO-2/3 observations for different surface conditions and terrain inhomogeneity, and how this can help us in optimizing radiometric calibration for the OCO-3 instrument.
Poster: Poster_Kurosu_0_143_25.pdf
Presentation Type: Poster
Session: 1.5a Results from current missions
Session Date: Monday (6/14) 12:00 PM