In this paper, the oceanic radiometric calibration biases of the Advanced Microwave Scanning Radiometer-2 (AMSR2) onboard the Global Change Observation Mission-Water (GCOM-W1) are analyzed. The double difference (DD) approach is utilized to perform inter-sensor inter-calibration for AMSR2 with the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) as the reference radiometer. This technique utilizes radiative transfer model (RTM) simulations and near-simultaneous clear-sky ocean-only observed brightness temperatures from the two microwave radiometers to estimate and correct the radiometric biases of ocean scenes for AMSR2 on a channel by channel basis.