An Independent Postlaunch Validation Methodology for ABI Thermal Emissive Surface Channels Using Moored Buoys Bulk Temperature Measurements

This work demonstrates the development of an independent post-launch validation methodology that can be used to characterize and monitor radiometric performance of the thermal emissive surface channels on the Advanced Baseline Imager (ABI). The ABI, NOAA’s new operational imaging system operated in geostationary orbit (GOES-East and GOES-West), has an onboard blackbody calibration target viewed repeatedly as imagery is collected that is used to implement the radiometric calibration algorithm. In support of efforts to ensure the post-launch performance of the instrument, a physics based approach that leverages high quality, free, and readily available data was developed to establish an independent validation of the operational calibration in close to real time.

This methodology propagates bulk water temperature measurements from moored buoys to predict at sensor radiance for clear sky conditions within the field of view of ABI as a function of time. Ground reference measurements of bulk water temperature are obtained from the National Data Buoy Center (NDBC) moored buoy fleet and propagated to water skin temperature using an empirical model. This value is converted to surface leaving radiance using Planck's law, water emissivity, and the instrument channel spectral response function. The surface leaving radiance is then propagated to a top-of-atmosphere (TOA) radiance using radiative transfer models that use input atmospheric profiles from the National Weather Service’s (NWS) National Centers for Environmental Prediction (NCEP) Environmental Modeling Center (EMC) Global Forecast System (GFS), to establish a predicted at sensor radiance. The predicted radiance (buoy observed bulk temperature propagated to TOA) is then compared to the observed radiance (from the ABI data of the buoy location) where a bias can be characterized for each validation point.

These established data sources are operationally available throughout the ABI field of view so this approach can be used to characterize radiometric instrument performance at various scene locations and view geometries throughout the day and over an extended period of time. This method can also be extended to establish inter-comparisons with other Earth observing systems. This work includes the development of this methodology, a brief discussion of the errors associated with the approach, and initial independent validation results. Inter-comparisons and continuous monitoring of GOES-16 and GOES-17 ABI thermal emissive surface channels using moored buoys as ground reference sites provides new operational post-launch capabilities to ensure both L1b and L2+ product performance.