Improving Collocation-Based Scan-Dependent Intercalibration Over the Ocean for Spaceborne Radiometry

Intercalibrating multiple radiometers using data from collocated oceanic fields of view has been a critical method for assessing in-flight instrument performance and reconciling constellation data. In this letter, we present a simple and effective improved method for radiometer intercalibration and apply it to the Global Precipitation Measurement (GPM) Microwave Imager (GMI), the core radiometer of the GPM constellation. By optimizing the collocation criteria, this method is able to produce improved scan-dependent calibration as indicated by the ability to characterize small-scale anomalies and edge-of-scan biases within GMI observations. The accurate characterization of scan-dependent calibration also allows further examination of the intercalibration dependence on brightness temperature (TB). An effective novel method using the cumulative distribution of TBs is used to examine the impact of TB on scan-dependent calibration. It is shown that intercalibration is dependent on TB; however, the GMI magnetic anomalies are additive signals independent of TB and therefore can be corrected by simply subtracting it from the data.