Improved Spatial Collocation and Parallax Correction Approaches for Calibration Accuracy Validation of Thermal Emissive Band on Geostationary Platform

Calibration accuracy validation (CAV) can usually be realized by intercalibration between different satellites. Under the framework of Global Space-Based Intercalibration System (GSICS), two modifications, improved spatial collocation with variable weighting (VW) and parallax correction (PC) approaches, to enhance the CAV performance are proposed. Distinguished from the uniform weighting method recommended by GSICS, the proposed VW one establishes a novel way of overlapping identification and overlapping area computation that is widely suitable for measurements from both the same and different platforms. Simulations indicate that the uncertainty of the VW method behaves better for the collocated targets far away from satellite’s nadir with a certain geolocation error, and is superior to 0.6 K for most overlapping situations when the geolocation error is less than 0.5 pixels. Case application shows that the VW method can significantly alleviate the uncertainty of assessed biases in brightness temperature (BT) by around 0.1–0.3 K for target nonuniformity larger than 2.5%, where the optimal bias estimation can be implemented with its uncertainty as little as possible. Besides the uncertainty improvement, the PC approach has the capability to reduce the bias of CAV by around 0.2–0.3 K, especially for BT range lower than 220 K with a limited number of paired samples. Long-term results show that the monthly biases of FY-2E and FY-2G satellites were superior to 1.5 and 1.0 K, respectively, where the mean monthly absolute biases of FY-2G IR1-IR3 bands were 0.4, 0.6, and 0.5 K, respectively. The proposed VW and PC methods are recommended for GSICS utilization and will further benefit to a more comprehensive community.