Robustness of the vicarious cold calibration algorithm in the double difference method for GPM inter-calibration

The robustness of the double difference method used for inter-calibration of microwave radiometers in the Global Precipitation Measurement (GPM) mission is analyzed. The double difference provides a way to compare two different radiometers and is more accurate than just a direct comparison. This is due to the double difference being able to remove geophysical variability from a radiometer´s data, as well as frequency and incidence angle dissimilarity between radiometers that would otherwise get included in a direct comparison. These variations are removed by incorporating radiometer modeled brightness temperatures into the inter-calibration process using a vicarious calibration technique. This analysis shows how well the modeled radiometer data is able to remove these variations as well as how well the double difference method performs compared to a direct radiometer comparison.