Inter-Satellite Microwave Radiometer Calibration Between AMSR and TMI

There are many satellites in orbit using total power microwave radiometers with external calibration targets. Pre- launch and on-orbit calibrations have been developed and applied to ensure accurate measurements over decades. But because of different designs as well as instrument aging effects, subsequent calibration is necessary to improve or maintain measurement accuracy. In-orbit inter-satellite radiometric calibration techniques could provide a long-term, group-wise solution. This paper presents our current research, which analyzes two methods to perform this calibration based upon coincident brightness measurements. In the first approach we build a transfer relationship based on three adjacent frequency measurements and major environmental parameters using radiative transfer model normalization. In the second approach, a linear regression is used among all frequency and both polarization measurements and their transforms. We utilize Radiative transfer models (RTM´s) in both methods, and refine them under different environmental conditions and later, we test the RTM models in order to better simulate brightness temperature retrieval before use in building transfer relationships. We validate the two different approaches by comparing external measurements between AMSR on ADEOS-II and TMI on TRMM. Results of calibration comparisons are provided along with accuracy prediction and error source analysis. By pursuing this research, the feasibility of building calibrations between polar-orbit satellites can be established for improved operational and scientific utilization of microwave radiometer measurements.