The GOES-17 Advanced Baseline Imager (ABI) has an anomaly with its on-board cooling system that prevents it from maintaining its Focal Plane Modules (FPMs) at cold, optimal temperatures. Because of this, during certain times of the year the FPMs and their detectors warm and cool throughout the day. Changing the detectors’ temperature changes their response to incoming radiance, which leads to calibration errors over time and degrades the imagery. Numerous mitigation strategies have been implemented to reduce the solar insolation on the instrument and to mitigate image degradation, including semi-annual yaw flips and changing the integration time of the detectors twice daily. These and other mitigations all work with the baseline calibration algorithms currently in place on the GOES-R Ground System. In an attempt to reduce the image degradation even further, the ABI vendor designed a new calibration scheme that predicts key parameters forward in time to account for the drifting FPM temperatures. These parameters, the linear gain term and dark current scene, are nominally updated on orbit every 5 minutes and 30 seconds, respectively. However, even at these relatively short cadences the detectors can change temperature, thereby rendering the parameters invalid for accurate calibration. By projecting these parameters forward in time the radiometric bias is reduced and image quality improves. This Predictive Calibration modification was deployed to operations on July 25, 2019, following several months of extensive testing and optimization by the GOES-R science teams. During this time several parameters and thresholds were tuned to ensure Predictive Calibration was turning on and off at the optimal times. Since going into operations users have seen noticeable improvement to the imagery and its calibration. This paper will discuss the fundamental assumptions behind the baseline equations and highlight the changes introduced by Predictive Calibration. Results will show the improvements to the calibration of the operational L1b products and reduction in image degradation.
GOES-16, the first new generation of NOAA’s geostationary satellite, was launched on November 19, 2016. The Advanced Baseline Imager (ABI) is the key payload of the mission. The instrument performance and satellite intercalibration results show that infrared (IR) radiances are well calibrated and very stable. Yet during its early post-launch tests (PLT) and post-launch product tests (PLPT) period, several calibration anomalies were identified with the IR bands: 1) the IR measurements of the Continental United States (CONUS) and mesoscale (MESO) images demonstrated an artificial periodicity of 15 minutes - Periodic Infrared Calibration Anomaly (PICA), in line with the Mode-3 timeline; and 2) the calibration coefficients displayed small discontinuities twice a day around satellite noon and midnight, which resulted in slight detectable diurnal calibration variations. This work is to report our investigation to the root causes of these anomalies, validation of the anomaly corrections, and assessment of the impacts of the corrections on the radiance quality. By examining the radiometrically calibrated space-swath radiance collected from the moon chasing events, it was found that these anomalies were attributed to the residuals of the spatial uniformity corrections for the scan mirrors. A new set of scan mirror emissivity correction Look-Up Tables (LUTs) were later delivered by the Vendor and implemented operationally. Further analyses showed that the new emissivity LUTs significantly reduced the periodic radiometric variation and diurnal variations. The same method will be applied to validate the IR spatial uniformity for the future GOES-R series ABI instruments.