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Earth-viewed images acquired during a recent asteroid-intercept mission present a unique opportunity for radiometric calibration of visible imagers onboard a space exploration probe. Measurements from the CERES-consistent DSCOVR-EPIC imager act as a reference in providing spatially, temporally, and angularly matched radiance values for deriving OSIRIS-REx-NavCam sensor calibration gains. The calibration is accomplished using an optimized all-sky tropical ocean ray-matching technique, which employs complex pixel remapping, navigation correction, and angular geometry consideration. Of critical consideration in this specific inter-calibration event is the extreme difference in spectral response function (SRF) width between the NavCam and EPIC imagers, which could cause a rather large bias. The NASA-LaRC SCIAMACHY-based online spectral band adjustment factor (SBAF) calculation tool provides an empirical solution to such potential spectral-difference-induced biases through a high-spectral-resolution hyperspectral convolution approach. The adjustments produced from this tool can effectively reduce the calibration gain bias of NavCam2 by nearly 6%, thereby adjusting the NavCam2 sensor to within 3.2% of its pre-launch calibration. These results highlight the capability of the SBAF tool to account for exceptionally disparate SRFs.

The CERES measured shortwave and longwave fluxes rely on the cloud properties derived using the coincident observations from the accompanying high-resolution MODIS and VIIRS imagers. The calibration consistency is required between MODIS and VIIRS radiances to ensure that the CERES provided cloud property retrievals are temporally consistent. This paper presents multiple approaches of cross-calibrating the spectrally comparable reflective solar bands (RSB) of Aqua-MODIS and NPP-VIIRS, and estimates the radiometric biases for individual band pair. The inter-comparison is performed between the Aqua-MODIS collection 6.1 level 1B and NPP-VIIRS Land PEATE V1 datasets. Radiometric biases up to 3% were estimated between the MODIS and VIIRS radiances for visible bands.

The AVHRR satellite data spans nearly 40 years, and is critical for studying decadal climate change, provided that the multiple AVHRR sensors are calibrated on a consistent radiometric scale. Because the AVHRR instruments lack onboard calibration capability, the radiometric scaling of the AVHRR record is feasible only using vicarious approaches. This paper presents a consistent radiometric calibration of the AVHRR visible (VIS) and near-infrared (NIR) records based on ray-matching, invariant deserts, and deep convective clouds (DCC) techniques that are referenced to Aqua-MODIS collection-6 (C6) calibration.

Post-launch calibration and characterization of Geostationary Earth Observing (GEO) satellite sensors, which lack on-board visible calibration, is a keenly felt need in many applications for studying long-term global climate changes. This paper proposes a vicarious technique of calibrating GEO visible sensors for the Clouds and the Earth's Radiant Energy System (CERES) project, using a kernel-based bidirectional reflectance distribution function (BRDF) model derived over an invariant desert site. The technique is illustrated with two Meteosat-9 visible channels, 0.65um and 0.86um, whose radiometric gains have been computed using a BRDF model of Libya-4 desert site. The Libya-4 BRDF model is TOA based and is derived from ten years of clear-sky Aqua observations over this site. The calibration results are validated by a direct comparison with the corresponding gains derived from the GEO-to-MODIS ray-matching technique.