Verification and recalibration of HY-2A microwave radiometer brightness temperature
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HY-2A is the first one of the Chinese HY-2 ocean satellite series carrying a microwave radiometer (RM) to measure sea surface temperature, sea surface wind speed, atmospheric water vapor, cloud liquid water content, and rain rate. We verified the RM level 1B brightness temperature (TB) to retrieve environmental parameters. In the verification, TB that simulated using the ocean-atmosphere radiative transfer model (RTM) was used as a reference. The total bias and total standard deviation (SD) of the RM level 1B TB, with reference to the RTM simulation, ranged -20.6–4.38 K and 0.7–2.93 K, respectively. We found that both the total bias and the total SD depend on the frequency and polarization, although the values for ascending and descending passes are different. In addition, substantial seasonal variation of the bias was found at all channels. The verification results indicate the RM has some problems regarding calibration, e.g., correction of antenna spillover and antenna physical emission, especially for the 18.7-GHz channel. Based on error analyses, a statistical recalibration algorithm was designed and recalibration was performed for the RM level 1B TB. Validation of the recalibrated TB indicated that the quality of the recalibrated RM level 1B TB was improved significantly. The bias of the recalibrated TB at all channels was reduced to < 0.4 K, seasonal variation was almost eradicated, and SD was diminished (i.e., the SD of the 18.7-GHz channel was reduced by more than 0.5 K).
KeywordHY-2A microwave radiometer brightness temperature (TB) verification calibration
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The authors would like to thank the Remote Sensing System for supporting the WindSat environmental products and RTM. We also acknowledge JIN Xu from the China Academy of Space Technology (Xi’an) for helpful discussion on the characteristics of the HY-2A scanning microwave radiometer. The author Yili ZHAO thank the China Scholarship Council for supporting this study at LOPS/IFREMER in France.
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