Extension of Vicarious Cold Calibration to 85–92 GHz for Spaceborne Microwave Radiometers
Extension of Vicarious Cold Calibration to 85–92 GHz for Spaceborne Microwave Radiometers
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DOI：
10.1109/tgrs.2013.2267152
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发表时间：
2013-06
影响因子：
8.2
通讯作者：
Rachael A. Kroodsma;D. McKague;C. Ruf
中科院分区：
文献类型：
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作者：
Rachael A. Kroodsma;D. McKague;C. Ruf
分析了85-92 GHz频率范围内的替代冷校准。由于对水蒸气和水凝物散射的敏感性更高，在这些频率下不能像在较低频率下那样容易地应用替代冷校准。通过选择性过滤高频亮度温度 (TB) 以消除存在大量水蒸气和/或水凝物散射的数据，可以减轻该灵敏度的影响。提出了潜在的过滤算法，并表征了每种算法在替代冷校准 TB 稳定性方面的性能。基于散射的降水过滤器结合使用了 19 至 37 GHz 的较低频率和 85 至 92 GHz 的频率，被证明是最有效且最容易实现的过滤器。对于水平极化，较高频率下的理论最小 TB 发生在非物理性的高海面温度 (SST) 下，这使得替代冷统计数据对实际 SST 值的总体以及与温暖 SST 相关的大量水蒸气更加敏感。在这种情况下，通过考虑观察到的和模拟的替代冷结核病之间的差异，统计数据得以稳定。当使用降水滤波器时，在高频下使用替代冷校准双差法的两个辐射计之间的相互校准被证明得到了极大的改善。
Vicarious cold calibration in the frequency range of 85-92 GHz is analyzed. Vicarious cold calibration cannot be applied at these frequencies as easily as at lower frequencies due to greater sensitivity to water vapor and hydrometeor scattering. The effects of that sensitivity are mitigated by selective filtering of the high-frequency brightness temperatures (TBs) to remove those data where large amounts of water vapor and/or hydrometeor scattering are present. Potential filtering algorithms are presented, and the performance of each with respect to vicarious cold calibration TB stability is characterized. A scattering-based precipitation filter that utilizes a combination of both the lower frequencies from 19 to 37 GHz and the frequencies from 85 to 92 GHz is shown to be the most effective and easily implemented filter. For horizontal polarization, the theoretical minimum TB at the higher frequencies occurs at an unphysically high sea surface temperature (SST), which makes the vicarious cold statistic more sensitive to the population of actual SST values as well as the higher amounts of water vapor associated with warm SSTs. The statistic is stabilized in this case by considering the difference between observed and simulated vicarious cold TBs. Intercalibration between two radiometers using the vicarious cold calibration double difference method at high frequencies is shown to be greatly improved when using the precipitation filter.