A Bias Correction Method for AMSR2 Brightness Temperature Over Global Ocean and Its Impact on Ocean Surface Roughness Estimation

It has been reported that brightness temperatures (TBs) measured by Advanced Microwave Scanning Radiometer 2 (AMSR2) show discrepancies compared to those measured by other microwave (MW) radiometers. To address this issue, the interconversion coefficients between AMSR2 and AMSR-E were developed by Japan Aerospace Exploration Agency (JAXA) and have been applied in many studies. Despite this, this study shows that the single differences (SDs) remain in AMSR2 TBs even after applying the JAXA-provided coefficients. In this study, a set of bias correction coefficients for AMSR2 is fit for each <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$20^{\circ } \times 20^{\circ }$ </tex-math></inline-formula> grid box to eliminate these residual SDs over the calm global ocean. The root-mean-square differences (RMSDs) between the observed and simulated TBs are significantly reduced after applying the bias correction scheme developed in this study by at least 64.40% at 7.3-GHz v-pol and at most 86.42% at 10.65-GHz v-pol during descending orbits. The estimation of two-scale roughness after the bias correction agrees with the physically expected values, demonstrating that the bias correction of AMSR2 TBs from this study can improve the accuracy of oceanic parameter estimation.