Using TRMM-VIRS Window-channel Radiances to Uniformly Calibrate Geostationary Infrared Sensors at Every Hour

Accurate characterization of the Earth’s radiant energy is critical for many climate monitoring and weather forecasting applications. Therefore, in order to facilitate reliable, climate-quality retrievals, it is important that consistent calibration coefficients across satellite platforms are made available to the remote sensing community, and that calibration anomalies are recognized and mitigated. One such anomaly is the infrared imager brightness temperature drift that occurs for many geostationary (GEO) satellite instruments near local midnight. This anomaly has been extensively documented, with corrections offered, for the Geostationary Operational Environmental Satellite system (GOES) series of satellites, and is thought to be caused by solar heating of the instrument. Owing to the diurnal dependency of this midnight inconsistency, the commonly referenced calibration standards, as proposed by the Global Space-Based Inter-Calibration System (GSICS) community, are insufficient. The Infrared Atmospheric Sounding Interferometer (IASI) and Atmospheric Infrared Sounder (AIRS) hyperspectral reference standards cannot be used to resolve the calibrations over all hours of the diurnal cycle given their MetOp/Aqua platforms are in late-morning/early-afternoon sun-synchronous orbits. The precessionary orbit of the Tropical Rainfall Measuring Mission (TRMM) Visible and Infrared Scanner (VIRS), however, allows for full local diurnal sampling over 46 days. Thus, VIRS has the capability of providing hourly temperature adjustments for concurrent GEO sensors in order to mitigate the midnight effect. To achieve this goal, VIRS is compared with Aqua-MODIS, thereby ensuring that VIRS IR measurements were stable between 2002 and 2012. Furthermore, VIRS IR calibration artifacts, i.e., temperature dependencies, are characterized and corrected by first calibrating with IASI. The validity of this methodology is tested through direct comparisons of GEO/VIRS diurnally adjusted temperatures with measurements from IASI